#446 – An Interview with Pete Bevelacqua

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Chris Gammell: Welcome to the Amp Hour. I'm Chris Gammell of Contextual Electronics. Hey, and I'm Pete Bevilacqua of antennatheory.com. Hey, Pete, how you doing?

Pete Bevelaqua: Pretty good. How are you? It's good to talk to you. I've been, you know, scouring the internet to learn more about RF these days and came upon your site and remembered that, oh, I actually, I know this guy. I met you, you gave a talk at HDDG back a couple years ago now.

Chris Gammell: Yeah, that was fun. I was building a VNA, so Vector Network Analyzer, which is actually one of the most critical tools for measuring RF or, you know, antenna. So I just kind of frustrated that super high cost, decided to build my own and ended up hanging out with you guys for a while.

Pete Bevelaqua: Yeah, yeah, that's good. It's great talk. We'll definitely link it in as well. But, well, let's, let's start back, you know, how, how did you get into this? So you are an antenna designer for various, so can you list some of the places you've, you've designed antennas in the past?

Chris Gammell: Yeah. So I worked at Boeing originally doing defense and, you know, antenna design there is more about like minimizing coupling between antenna systems as opposed to design because they just have a lot of space. Then I went to Apple, was there for several years, worked on the Mac mini and a bunch of different iPhones, some other stuff. Was at Nest for a while, did, you know, different things there and worked on some wearables as well. So a lot of consumer electronics mainly, but familiar with, you know, defense and other various applications.

Pete Bevelaqua: Yeah. And so did you get started at the beginning of your career? Like, were you always like, not RF's where it's at, that's where I'm going into. Like, where did you get started in all this?

Chris Gammell: Uh, yeah. So, well, so taking it from the time I started as like going into electrical engineering, like I, I really liked like electromagnetics. And so I was just kind of drawn to that. I like that more than like circuit design, for instance. Um, so I, I kind of liked just the math based problem solving. I thought it was cool. And I didn't know much about antennas at the time, but so I was taking like, uh, those classes as an undergrad. I went to Stanford for my master's and I took an antenna class, but it was really bad. Yeah. So like I came out of there and, uh, I remember thinking like, I don't know much about antennas cause it was really theoretical. It was like, sure. You know, here's a show that the fields from a small loop antenna are the same as a small dipole antenna. If you switched H and E and it's like, okay, that's cool. Can I design an antenna? Nope.

Pete Bevelaqua: Yeah. Like when do I need to do this in the real world? Right.

Chris Gammell: Well, and just the fact that like, you know, you take the class and you do well, but you come out and it's like, do I know how to put an antenna in a phone? And the answer is no, you know? And so I wasn't, so then, you know, I was kind of into signal processing for a while and it just so happened I ended up at, uh, Arizona state and, uh, there's a famous antenna professor Bilanas who wrote like an antenna textbook. So I started chatting with him and ended up joining his research group. And so my PhD I was like able to combine like signal processing stuff, like convex optimization techniques to antenna array optimization and ended up fitting together really well. So I was able to, you know, uh, you know, kind of merge two fields in a way that hadn't quite intersected yet. So that was pretty cool. Um, but yeah, so it wasn't like I loved antennas or knew that I was going to do antennas. It was, uh, you know, I had an interest in electromagnetics and then antenna opportunities just started coming up. So then when I was looking for work, like Boeing antenna engineer was there, uh, you know, just

Pete Bevelaqua: kept going. Yeah. Yeah. That's great. So the, uh, tell me about ASU. I mean, so the, the research, I didn't quite understand what you're talking about there. So the convex piece, what was that?

Chris Gammell: Yeah. So at Stanford, they have like a really big convex optimization program or like the leader in convex optimization research works there. And it's part of the EE department. It's basically like, um, a really kind of general glass class of problems where you can guarantee a global optimum solution. If you can frame a problem in a certain way, which is convex. So like optimization problem, basically like minimize an objective function subject to some constraint and a convex optimization problem means the objective function is convex and the constraint set forms a convex set. With those two properties, um, it's actually really like broad class of problems and you can guarantee a global optimal, uh, solution, which is, uh, super useful. So anyway, so when I went to Arizona state, I started working on antenna rays and figuring out like, how can we make the lowest possible, you know, uh, side lobes given a beam with for a fixed number of elements or whatever. I was able to apply this, you know, convex stuff, uh, to antennas and, you know, write some cool papers.

Pete Bevelaqua: Yeah. And so that's kind of the, what I, you know, pairing up that, what sounds like very theoretical, the convex optimization with the practical, like you're saying, um, could you give some more examples of how the convex optimization might be used in the real world, like on a daily basis?

Chris Gammell: It's used a ton in signal processing. Um, so finding weights that like, there's probably optimization algorithms and, you know, all the, uh, you know, how our voice is being processed right now.

Pete Bevelaqua: Oh yeah. Yeah. Avoid codec or something.

Chris Gammell: Yeah. So, um, uh, I'm not super familiar with like all the applications, but, you know, at least in, uh, for antenna rays, we're able to apply it to, you know, determining optimum weights and corresponding optimum positions that work together.

Pete Bevelaqua: Okay. And does this relate to like, um, to like matrix math around, around the optimizations? Is that the context?

Chris Gammell: Yeah. Uh, well, so if you have like a constraint set, like a X is less than or equal to B where X is your, um, you know, variables you're optimizing over, that's like a linear optimization. So there's like a whole set of optimization problems called linear that are linear programs. And so then you would have like matrix constraints and stuff. So, um, convex is just a bit more general than that.

Pete Bevelaqua: Okay. Huh. That's great. That's great. Yeah. Cause it's, it's interesting to me. Like, I feel like a lot of the, um, a lot of the math that is inside of like a lot of the, the field solvers and all this stuff that's out there, it's kind of hidden from, from people that are using them on a daily basis, but having that like low level understanding, like you're talking about could be really useful from knowing what to tweak and how to, how to tweak it. Yeah. That's great. Okay. So, uh, Boeing, uh, I've, I've heard of this Boeing. Uh, so you had mentioned that it was like a lot of, it was about making sure that you don't interfere with one radio to the next.

Chris Gammell: Particularly like on the defense side. So, um, you know, so there'll be like, Oh, we want to take a certain airplane and we want to add like 20 antenna systems to it. Oh my God. Yeah. Cause that's what they do. Right. And they have just a ton of radars and communication systems with everything, like all sorts of GPS stuff, just, you know, satellite community, every communication system you can think of, they'll put on there. And so an airplane is pretty big. So, um, you know, you're not necessarily like space constrained. Um, but so like what we would do there is we spent a lot of time, like, okay, if we put the antennas here, this is our field of view. And so it's like, what locations are not obscured by the wing or, you know, tail or whatever, and then figure out like, okay, what's the coupling between these two systems? Cause that'll determine like whether they can work at the same time, you know, coexistence or what level of filtering you need

Pete Bevelaqua: to enable them to work at the same time. Okay. Yeah. And, and like, what are, uh, what are some of the frequency ranges that we're like talking about here? Like for military? Uh, well, they always say

Chris Gammell: DC to daylight, but what that means is, uh, like, you know, I would say like 20 megahertz on the low end, uh, like 40 gigahertz or a little bit higher on the high end. Yeah. Wow. Okay.

Pete Bevelaqua: And then that was the same thing where you had to figure out like, is the 20 megahertz interfering

Chris Gammell: with 40 gigahertz and all that kind of stuff? Yeah. Well, in that case, there's so much frequency space. You're probably okay. But like some of the radars would have like, you know, blast like kilowatts of power, which is right. Right. You know, 60 dBm. Then we have like a radio next to it. It was sensitivity is like minus 110 dBm for instance. And, you know, so you might have, you know, need like 200 dB of filtering or something. And that's where you're like, okay, we can't operate these systems at the same time. Right. Hmm. Yeah. And I mean, uh,

Pete Bevelaqua: so you also run the antenna theory website and, and stuff like that. And so like when you are thinking about, uh, getting people started in this kind of stuff too, like, so, so just talking about like filtering and antenna theory and, and, and everything else, um, you know, where do you usually have people start? So like, like that question I just had about like, you know, low, low frequency versus high frequency and how they interact and stuff like that. Like how, how is it the, uh, you know, where do you usually tell people to kind of, to get into that, that element of things?

Chris Gammell: Yeah. So, I mean, I would say like, everyone's going to start with a specific problem and then kind of dig it over there. So like a lot of people are like, Hey, I want to put a Bluetooth antenna in my device. And so there you want to understand like just the fundamental rules of antenna design. Like, Hey, having a halfway length is good. Don't put metal right behind your antenna. And you know, if you're on the other side, like RF where you're like, Hey, I want to know if two systems work at the same time, then you say, okay, well here's the two frequencies, you know, figure out like what the roll off of the transmitter is from your data sheet and what the sensitivity is on the other side and figure out like what level of filtering there is, you know, search digit key to see if you can find a filter with those parameters. You know, a lot of it is like, you have to start like with a specific problem in mind, like the whole, you know, like if you just want to learn antennas in general, then yeah, it's like go to the antenna theory.com and just start flipping through it and learn the basics. So, you know, like the terminology and what's key. But if you're doing a specific problem, I would say, Hey, just see how far you can get and then start pinging people from there.

Pete Bevelaqua: Yeah. Yeah. That's good. Okay. Yeah. I mean, um, because we'd like, uh, people that listen to this show are kind of all, all over the map. We have some people who are absolutely beginners and some people that are listening to you and being like, yeah, I do what Pete does. Uh, so it's always an interesting mix as well. You try and give, give people a good basis to start from. Um, when you, when you approach a problem though, as well. So say like, let's just use the Bluetooth example there. Yeah. When you approach a problem, does it start from a place of practical or does it start from more of a place of math? Like, and you specifically as a

Chris Gammell: definitely practical. So like if I need to put a Bluetooth antenna in a product and there's no constraints, like it's some plastic small thing and I can do whatever I want, then you don't need anybody with any level of intelligence, right? It's, it's simple. All right. Like the rule number one, this is, this sounds like me. Do not make anything hard that does not need to be hard. So like there's nothing wrong with going to digi-key typing, you know, Bluetooth antenna or whatever, putting that on your PCB and then following like the key pounce for, you know, what's on the PCB like that works. Yeah. So there's no reason that you don't need to do that. And Bluetooth is kind of pretty robust in the sense that, you know, if you're only trying to go 10 feet, you're going to have more than enough link budget. It's not going to be that big. Don't make it hard. Got it. But it's like when you start like packing multiple systems in a product or you have very small keep out, you're trying to, you know, you might have like metal in the product. That's when things can get very difficult. You know, it's like when you're really trying to integrate a lot of different systems or really push the envelope on a tight integration, that's when it becomes hard. Right. But just if someone's like, Hey, let's put a Bluetooth antenna in a product that doesn't necessarily need to be hard. It could be very simple.

Pete Bevelaqua: Okay. Yeah. That's great advice. And I think that that, uh, the hard stuff like, like you were talking about, it sounds like that's kind of what you get paid for as, as an antenna designer, as an engineer, you're, you're digging in your, you're probably still applying a lot of that practical knowledge that you have, but then you know, you're like, okay, now we're in a corner case and now we have to do testing and now we have to do this and that.

Chris Gammell: Yeah. Well, the one piece of math is, you know, whatever technology you're using, Bluetooth, GPS, cellular, you want to know like what the lowest frequency is that you're using. So GPS is 1.5, 75 gigahertz or whatever. So the antenna engineer immediately thinks, Oh, okay. That's like three and a half, three and three quarter inches or whatever for a halfway thing. So I'm immediately thinking, okay, that's about the size that I need for a decent radiator. So if someone comes in with like a product, the size of like a quarter and they want GPS in there, then I know they're going to have huge efficiency problems. Got it. And so efficiency, by the way, is just a ratio of how much power you're putting into the antenna versus how much it actually radiates. Okay. Yeah. That's the key parameter in antennas is

Pete Bevelaqua: efficiency. Right. And that's probably also pushing back into like how much bad, like if you're on a plane, right. And you have, you know, a generator on board, you probably have a lot more power available than like a tiny Bluetooth device, right?

Chris Gammell: Up to like, again, FCC limits, right? So you can't take a Bluetooth device and put out, you know, two Watts, for instance, it won't let you do that.

Pete Bevelaqua: Right. I just mean that like, if you have a 10, 90, sorry, a 10% efficient antenna and you put in, you have to put in like a watt in order to get out a hundred milliwatts, like you're still burning, you're burning 900 milliwatts in that case. And you could do it even with a low efficiency antenna,

Chris Gammell: right? Yeah. Yeah. For Bluetooth. Yeah, you're fine. The link budget. Okay. We're talking like a decent link budget for Bluetooth is like a hundred DB is you might have plus 10 DBM output power. That's what? 10 milliwatts. And the sensitivity on the other side is minus 90 DBM. So, you know, you can get away with a lot of, you know, sketchiness a little bit. And then you mentioned something about percent. So that leads me to a rant I must give is everything in RF is DB. So you have the output power, DB, DBM, whatever. And then you have the loss or the path loss. It's always like 90 DB or something. Then you get to the RF side on the, and you have an LNA with, you know, 10 DB of gain and then insertion loss of a filter of three DB. And then you get to the antenna and all of a sudden it's percent. So that to me, it's like, I don't like it for that reason. So I always say antenna DB, antenna efficiency and DB just because everything is DB. So I don't know why they use percent. So really it should be antenna efficiency should be insertion loss or whatever. And then the other thing I don't like about, uh, efficiency is if in percent is if you're talking to someone like, Oh, how much will this change affect your antenna? They'll say, Oh, it's just a couple of percent. That actually doesn't mean anything. Cause if you're going from like 2% to 4%, that's three DB. But if you're going from like 90% to 92%, that's nothing. Right. So, um, so for those two reasons, um, I usually, it always, I'm always like, no, don't say it percent.

Pete Bevelaqua: Yeah. That's, that's good. That's good to know. And I was, uh, I've been reading, I've been reading that book. I think I mentioned on the show by, uh, Tom Lee, uh, the planar microwave book. And he brought up something in there. It was like, DB is always capitalized because the B is bell as in like Alexander Graham bell. And I was like, Oh my God. Like that one little thing I was like, Oh yeah, that makes a ton of sense. I was wondering why it was like that. So capitalize your Bs folks. Uh, so, I mean, and, and so you work in, you know, decibels all the time. I mean, is that kind of how you think about the world now in terms of like the, yes, including like

Chris Gammell: meetings, like I'll be like, this meeting is 3DB too long. So like, yeah, I use DB for almost everything.

Pete Bevelaqua: Okay. How does that end up impacting like your, um, are there any times when you, aside from what you said, like the efficiency stuff being like percentage and, and, and that, is there any, anything else in the field that is linear or non, non logarithmic like that?

Chris Gammell: Um, in RF is like literally all DB. Um, yeah. Okay. Okay. I can't think of anything off the top of my

Pete Bevelaqua: that. Yeah. I'm just, uh, I, you know, switching into that mode for me has been, has been interesting, like thinking about it like that because it's, it's kind of, it's kind of foreign just in terms of like thinking like that, but it's, you know, there obviously it's filter theory too. It's, it is other places, but it's, uh, you know, it's a little bit foreign for me and, and switching into that mode is tough. So, um, so on the, uh, so going back to Boeing, like, uh, you have, so now we're talking about a plane, you've got 20 different antennas on there. Yeah. So now you as an antenna engineer, what is your, what does your daily kind of task look like? Is it, you know, are you designing custom antennas? Is it, is it testing what is out there? Yeah. You don't really

Chris Gammell: design the antennas anymore. So we'll be like, okay, here's a system with a big radar and here's a system that's a receiver. You know, if we put them, you know, like on these two locations, on the fuselage, then the isolation will be, you know, 60 dB or whatever. So then we can feed that information over and they're like, okay, we can either get enough filtering or we need more isolation between the antennas, which means change the placement and try again or figure out, uh, like, Hey, these two systems aren't going to work at the same time. So let's not even try to use a hundred dB of filtering, which is blank one or the other. Okay. So yeah. So that's kind of an example.

Pete Bevelaqua: And so like blanking, you mean like when one's on and then it has to be off, that kind of thing? Correct. Okay. Okay. That's cool. Uh, and you mentioned you never really design antennas. At Boeing. Yeah. Oh, okay. Is that because they-

Chris Gammell: I've designed a lot of antennas. I put a lot of antennas in products, so.

Pete Bevelaqua: Oh, okay. Yeah. We'll definitely get to that too. Uh, why is it not the case at Boeing? Is it because of the constraints on the design itself?

Chris Gammell: I guess you don't necessarily, I mean, you don't need to design an antenna because, um, like if you're putting an antenna in iPhone, there's no way you can type iPhone antenna into Google, buy one, and then start using that for instance. Like it's integrated into the chassis, into the product. You have to factor in every component in there when you're designing it. Whereas at Boeing, you can type, hey, I need a one to 18 gigahertz circular polarized spiral antenna. Um, you can type that into Google and get a few different options and then buy it and take it from there. Okay. So it's kind of like, yeah, you can make things hard, but you don't necessarily need to.

Pete Bevelaqua: Got it. So if it was like a very, very, very tiny airplane, then maybe you'd have to do it because you'd be etching the, etching the antenna onto the wing or whatever it is. But because in this case, it's huge enough to use by one.

Chris Gammell: And if you were like, look, there's no, like I only have this size window for the antenna. We cannot find that. So therefore we need to design our own. That's, that's a valid reason.

Pete Bevelaqua: Okay. All right. Yeah. And it's, and it, it is kind of like coming into shape of like the constraints you're dealing with. It's like other stuff being in the way, uh, the total size you have, the frequencies you're working with, are there other constraints that you thought about at Boeing that maybe you didn't have to think about at the consumer level products?

Chris Gammell: Um, well, the power is much higher. Okay. Sure. Yeah. Radar. So they have different like classes of, you know, amplifiers and all that. Um, I don't know, like, like in consumer, you're always much more worried about FCC limits. Whereas like, if you're working on the defense side, they don't have that as much. They get their own frequency bands and their own GPS frequencies and all that. Oh, I didn't actually know that. Okay. Yeah. There's like military

Pete Bevelaqua: bands for GPS. That's cool. Okay. Yeah. Um, yeah, that's, that's good. And then what about like, so you had mentioned like the polarization and like the directionality of an antenna as well. Like when you're, when you say you're, you are Googling around and you're shopping for an antenna, like, is it, uh, how, how is that kind of decision-making process made at least in, in that,

Chris Gammell: in that case of, uh, so the first thing is, you know, do you want a high gain antenna? And so, you know, if you're working at Boeing and you know, like you're communicating a point to point link and you know, the direction of the other, uh, antenna you're communicating with, then yes, you want high gain. Um, if you're making a router and it's talking to an iPhone, you don't want the iPhone or the router to have a high gain antenna. And that's because high gain means directional. And so if you don't know where the other side is, you kind of just want to spew energy everywhere.

Pete Bevelaqua: Okay. Yeah. Can you define the high gain in that, in that context as well? Cause I think about high gain just generally of like, okay, you're adding power to this thing, but you, you're saying it more

Chris Gammell: of a, like a directionality and like a focusing gain specifically is, uh, efficiency in dB plus the directivity in dB. Um, so for an example of efficiency of minus three directivity is always positive. Let's say it's six, then your gain is three dB. So minus three plus six gain is three. Um, so like in consumer high gain is like more than six. And the reason gain is actually bad is one, you're making the antenna more directional, which isn't great. Um, you don't want it to work in one direction and not another. And then the other is, uh, just FCC cert. So like a lot of the, uh, you know, rules require like, okay, your radiated power in a certain direction must be less than some, uh, level. So if you have a really high gain on your antenna, then that's bad because then you might have to back off how much power you're transmitting because your gain is too high and that's bad.

Pete Bevelaqua: Okay. Okay. And then, uh, yeah. And so, and you're, so you're saying that, uh, because you would just be spewing it in the one direction that you would have to take everything down total because

Chris Gammell: FCC. So they'll be like, okay, the limit is 30 dBm at, you know, so usually like you might have a problem at five gigahertz cause it's the smallest wavelength, which means the antenna is the largest at that frequency, which means the gain size. Um, so typically like the larger your antenna is, the higher the gain. So if you want a really high gain antenna, you need a big antenna. Um, does that make sense? I think so. Yeah. Yeah. Okay. So, uh, so because five gigahertz is the highest frequency typically like for wifi, um, that has the smallest wavelength. So the gain is always higher at five gigahertz than it is at 2.4 gigahertz for instance. So like FCC might say, Oh, the gain, the peak gain is 30 dBm that were allowed, uh, or the peak radiated power is 30 dBm, which they call EIRP equivalent isotropic radiated power. They make it complicated for no reason, but that's basically conducted power, which is how much power is coming out of the radio plus your antenna gain. So if for instance, you have eight dB of antenna gain and you're trying to transmit 24 dBm, then you're over the limit and you have to back off the conducted power. And that's bad because you don't actually have antenna gain. The antenna is a passive device. You're always radiate less power than what's coming out of your radio. So if you're conducted as 24 dBm, you're only, you know, your antenna efficiency is minus three. You're only radiating 21 dBm, but you still could be over the EIRP limit, which is what they require you to be at. So you have to back off the conducted power. So you have less radiated power coming out. That's bad.

Pete Bevelaqua: Yep. Uh, also don't want to, wanted to disambiguate as well. So you've been saying dBs and dBm and that always confused me as well. So that's a thousand less or, uh, it is, is context

Chris Gammell: based, but yeah, like, so when you say dBm, you're always referring to milliwatts and power. So, um, 30 dBm is, uh, one watt zero dBm is one milliwatt 10 dBm is 10 milliwatts. But when you're talking about antenna gain or efficiency, those are always dB because it's a strict ratio. There's no like antenna efficiency of dBm. That doesn't make sense. It's always dB because it's ratio of input to output

Pete Bevelaqua: power. Yeah, that's good. That's good. That's good to have that as, you know, as people are listening to, I'm sure that like a lot of this too is like, all right, well go and read on the antenna theory website. This is good for this kind of stuff. But, uh, yeah, that's good just as we're talking about these things. Um, okay. Yeah. And there's a great point about the FCC stuff and how that, that kind of impacts things in consumer versus, uh, versus the military stuff. Um, are there ever, um, so you said there antennas are always passive. So it's always about adding, adding power before

Chris Gammell: that with like an amplification stage. Is that right? Yeah. Okay. So in, at least in consumer, like RF and antenna team is two different teams. Okay. So RF team focuses on the board level, which is like the radio, all the amplifiers and all this. And, uh, then the antenna team focuses on the antenna. So there's like a strict like the military DMZ, the militarized zone between the two teams where they focus on the board level or focused on the antenna. Interesting. And so antenna team works more closely with product design, the mechanical engineers, cause we're really integrating that antenna. And that's a function of, you know, all the grounding around it, the screws, the flexes, all these things. RF team might work more closely with the EE team. Right. Delivering power, having clean power, that kind of thing. Yeah. But the RF team and the antenna team don't necessarily need to interact too closely. And again, like on the certification thing, like where the peak gain has to be below, that's a, that's an example where they would need to communicate. But RF team focuses on like measuring, uh, all their parameters in a 50 Ohm system. Okay. And the antenna team measures the antenna in a 50 Ohm system. Uh, when you hook it up, if both teams get it right, it just works.

Pete Bevelaqua: Got it. Got it. Okay. And that's, that's good to know as well. So, um, the, that's another thing I've been learning from this book as well about, I mean, I've, I read it before, I heard it before, but like I said, I haven't been working with it all that much, but the working with 50 Ohms as well, I hadn't actually, I didn't know the, uh, the origin of that, uh, 50 Ohms in the past.

Chris Gammell: Yeah. It's, it has to do with like power handling and loss, like the tradeoff between the two or

Pete Bevelaqua: something. Right. Yeah. I think one's there's like one of the, one of the parameters, 30 Ohms is the optimum. The other one 70 Ohms is the optimum. So they just split the difference instead. Yeah. Fun. Uh, that's cool. Uh, okay. So let's, well, you kind of started talking to the consumer side of things. So after, after Boeing, you went over to Apple and obviously a ton of the constraints

Chris Gammell: change. So what, what was that like? Um, I mean, it was wild. I mean, going from a place like Boeing, which they have a union for the engineers and product cycles are on the timelines of like 10 years to Apple where it's like one to two years, you know, that was, that was crazy. I was just like, wow, things move really fast here. So that was the biggest thing there, but yeah, it was just, um, it was totally different. Like it was like, yeah, we designed the antennas at Apple, you know, like they have an antenna team internally that starts with, you know, Hey, we want to put an antenna on this new product. Let's figure out what we need to do. And there's no custom antennas that are like, it has to be custom because they're always coming up with crazy industrial designs for everything. Right. Right. You know, you can't like, that's a very good case. We cannot go to DigiKey and buy an antenna and put it in a product and call it.

Pete Bevelaqua: Yeah. And so, okay. So, so let's talk about maybe the prototyping process and kind of like walk from prototype through production if you can.

Chris Gammell: So let me go to a high level, like consumer electronics and say, this is how it works. So, uh, in general, so near the top, you have the industrial design team. So they're the ones that are like, we want the computer to look like this and to have this materials to feel like this and do this. Um, and in conjunction with like the product team, which is like figuring out the business case. But so essentially it starts with industrial design. They have their vision. Like they want an all metal product, no gaps anywhere. So then, you know, from there, you know, they give it, you know, the product design team, which is mostly mechanical engineers start like figuring out, okay, how would we make this thing? And, um, all this at the same time, then like, uh, uh, antenna team will start working with, uh, similar sized, similar material, like mock-ups. So it's like, okay, let's say you're doing a computer. Um, and they're like, we want metal in all these regions. And you're like, well, we're going to need a gap somewhere for the antenna. So if they, if they provide no gap at all, then you have to like, kind of start. Right. You're like, this is a land-based product now. Or, you know, like one thing you have to do is like, if there's literally no space, you just put in an antenna and do your best. And then you say, Hey, look, so given this, the best we could do is an antenna efficiency of minus 20 dB. It's just not going to work. Wow. Okay. Yeah. So, you know, sometimes like, you know, you, you have to do that. And then, you know, in a healthy relationship, there's give and take. And, you know, you say, okay, well, we'd be willing to move some metal away here. Can you get this to work? And so it starts, there's a lot of iteration, I guess. Negotiation too, huh? Negotiation. But yeah, I mean, if everybody's aware of what the goal is, you know, like in it, for instance, in cellular phone, you can't ship an antenna that has like minus 10 dB efficiency because they have like the carrier set specs. It's like, it must radiate this much power. So you can't just squash it. So you can't ship it. Like if you just completely ignore the antenna.

Pete Bevelaqua: Okay. So, okay. So now you're at the point where, okay, you have a, you have an industrial design, you've negotiated a little bit of plastic or a little bit of a cutout so that you can get an antenna through.

Chris Gammell: Yeah. And you would have, well, you would at that point, you wouldn't just say, Oh, I think it would make it work. You would have like a mock-up or a simulation that says, Hey, given these volumes, here's what we're going to hit. We're committing to that. Once you're there and you're comfortable then, or at least, you know, everyone's on the same page, then, you know, then it's about integration, which is again, just as much, probably more work than the design itself. So the integration is like, okay, well now we're going to throw in the speaker and, you know, so you learn like what things are the biggest risk. So speakers, a lot of, you know, plastic and air. So those kind of interact well with an antenna. So if you open up like, you know, phones, you'll see like the speakers and the antennas coexist in the same locations, you know, and then like, okay, we're going to need the power cables going to go here. What happens when we plug in the power cable? Does it destroy the antenna? What can we do about that? Um, cause it's a channel of metal you're saying? Exactly. Yeah. And then, uh, you know, you just start figuring out like, okay, where's, you know, where do like you have like the metal on the back of the display, for instance, and the metal on the camera, like where are the critical ground points, uh, that need to be in there such that the antenna doesn't get degraded as we start, you know, uh, making this from like a kind of a mock-up that's just a shell to an actual

Pete Bevelaqua: product. Yeah. And you mentioned simulation. So that, I'm sure that's kind of like you keep revising that throughout time, but what are you, what are you using to simulate? Um, so personally I'm not a big

Chris Gammell: simulator, but, uh, the most common ones are HFSS and CST, I'd say. Um, so yeah, I mean, so I think simulation is good. You always have to confirm it with mock-up cause there's no way you can, you know, capture like all the, you know, like some, you might have some loss inside of flex that you can't capture in a simulation. You really need to build it and test it to ensure that, or like you, let's say you have a piece of foam grounding, you know, how do you know that foam is, you know, making the proper contact when it's actually in the product, you can't simulate that as well as you might hope. So simulation is a valuable tool, like definitely shouldn't say, you know, it's not, but you definitely have to confirm simulation with a mock-up.

Pete Bevelaqua: Yeah. It's like a starting point versus, uh, the be all end all kind of thing.

Chris Gammell: Yeah. So some people don't simulate at all. They just go straight to the mock-up cause they're like, Hey, I can, why do I need to do it that way? And that works. And some people, you know, do it where they rely more heavily on simulation. Um, you know, there's no right way. It's kind of like what people want to do based on their experience. And if you can ship products and you've done it

Pete Bevelaqua: before, then whatever works for you. Right. So when you're, when you're doing a, you say, you're not doing that much simulation like you do. So what is the alternative then? So it's, you have a mock-up, you have a test antenna in there and then you just kind of throw it on the bench or, or what are we talking about here? Yeah. So you'll, you know, like pick a product like, uh, let's use it like iPhone. If you, if you don't mind talking about that, that'd be great. We'll talk about a Samsung phone. Okay. Samsung phone. Uh, how about a generic Android phone?

Chris Gammell: Yeah. And we're going to talk about a windows phone. So let's say that sounds great. How about a Nokia, Nokia brick phone? Yes. So you have a Nokia phone, Nokia windows phone and it's on your desk. So first of all, there's not that many fundamental types of antennas. Like they're all basically like hybrids of dipoles and like a dipole is basically two wires that are in phase and hence radiate. And you start with that and you start like meandering it to fit in the package. And basically, um, you know, if you've worked on antennas, like if you're designing a cell phone, you should have, and you didn't have exposure before you would buy like 10 different cell phones, tear them down and figure out what's working, you know, measure the antennas on those, you know, you'll start to gain some knowledge. You won't have a lot of knowledge because just cause you can tear down like a phone doesn't mean, you know, what's the critical points in there, like which ground points are critical, which volume, uh, you know, like which components of the volume, like the height or the width are absolutely critical. And, you know, which flex really needed choked and all this different things. Um, so you, um, you can start to learn by doing, but let's, when you're like, you're working at Nokia, they give you a phone and you're like, Hey, I negotiated this volume, you know, you would essentially just, uh, cable it out, which means put a cable on the antenna and ground it to the PCB and all that. So it's your cables, not influencing, uh, the measurement. First thing is you put on a VNA vector network analyzer. That's where you can see the impedance. So that'll tell you like, if it's tuned properly. Um, so like if it's GPS, you'll say, you know, the impedance goes to 50 ohms or whatever. And then like, basically, uh, you'll hear antenna people talk about VSWR, um, or that's just basically the return loss, like a VSWR one is perfectly matched. So basically you're looking at a plot of VSWR versus frequency, you know, you see, oh, it goes down and it's matched at this frequency. So I can tune it up or down. Um, that first thing just tells you the antenna is accepting power. It doesn't actually tell you it radiates. So there's two things for an antenna. Radiate has to have a structure that supports radiation. And it also has to be matched to 50 ohms. So with the VNA, you can tell, Hey, it's matched. And so we're delivering power to the antenna, but it could also just be absorbing that power. Like if I put a 50 ohm resistor on a VNA, it'll be like, Oh, it's really well matched. Cause right. Yeah. So once it's matched, yeah. Once it's matched and you would measure, you know, you just go straight to measuring the efficiency and that's, um, done an anechoic chamber. So it's just basically, uh, you already have it cabled up the antenna cabled up in the product. You put an anechoic chamber, which measures like how much power is coming out from every direction, essentially, you know, integrates over it and tells you, Hey, this is how much power came out. And that's your efficiency. That's great. If you know the efficiency, uh, and then that's done it, you know, whatever number of frequency points you want, but you have your frequency, your efficiency and your impedance. And, uh, that's, that's it from there. You start iterating.

Pete Bevelaqua: So then, well, like the, the frequency, the different frequencies is also interesting to me. So like this windows phone, it's going to have maybe 2.4 gig for Bluetooth and maybe five gig for wifi as well. Like it more advanced wifi, but then also like a bunch of cellular frequencies and GPS frequencies. How do you, how do you get them all? Is it all one package or like, how do you, how do you start to cut all these things together?

Chris Gammell: Um, yeah. So wifi is at least for the last 10 years, always 2.4 and five gig. Um, typically on these phones, Bluetooth and wifi share the same radio and the same antenna. Yep. Uh, GPS is 1.5, 75 gigahertz. That's can be, that's usually 50, 50. It's its own antenna or shared with wifi or cellular. Um, so there's typically, um, you know, you know, the bands coming in. So it'll be like, okay, we need GPS, wifi, it might be NFC and cellular, and they'll tell you the cellular bands. So if you're shipping a phone in the U S it actually used to be much simpler before LTE, there's only like five bands since LTE came out. So complicated. 15 plus bands. No, there's so more. He was like, I defy anybody working on a phone and 2019 to tell me all the bands that are on their phone. Oh really? Actually. Yeah. Somebody call me up, the antenna designer and you can list all the bands on your phone. I'd be pretty impressed. No, it's crazy. Okay. But anyway, for an antenna engineer, it doesn't matter. Cause you're like, okay, well that translates to this set of frequencies. And so therefore we have to hit this set of frequencies.

Pete Bevelaqua: Well, so like there's what, like, it's like 1750 or 1800. Is that one of the, or sorry, like a 1.8 gigahertz. Is that, that's like one of the frequencies, right? But does it need to be just that one frequency or can it be like, like sensitive over, you know, from the 2.4 or sorry, like the one point, what the one gig up to three gig or something like that?

Chris Gammell: Yeah. I mean, you could make an antenna sensitive across a ton of bandwidth. That's good. You don't lose anything. Okay. Yeah. You don't lose anything. Uh, you know, you might need some filtering there or whatever. Okay. So it's not, it's not the job of the antenna

Pete Bevelaqua: to reject anything you're saying. You're just trying to make the best, the best transmitter

Chris Gammell: available kind of. Exactly. Cause filters do a way better job. Antennas like slow roll off versus frequency. So you do not use the antenna for, you don't rely on the antenna for rejection. You have to rely on the filtering. Got it. Okay. Um, but yeah, so you mentioned like 1850s. Yeah. So in that spectrum, like just say 1850s, like when I say there's so many bands, like there's probably like 10 different bands that sit on 1850. Yeah. Cause there's like 2g, 3g, 4g, you know, 5g now, like all these CDMA, all these different ones that sit on the exact same frequency. And then

Pete Bevelaqua: there's like the EU is slightly shifted from that's right. Yeah. 1900 versus 1850. So I remember like, I used to deal with these a little bit more, but yeah, there's a lot. Six, seven years ago,

Chris Gammell: like iPhone one, two, three time, there was only like four bands. It was like, yeah, like two, 2g bands, two 3g bands. That was about it. So does that end up impacting you other than like

Pete Bevelaqua: make you have to like double check that you make sure you're testing for each of these, these, um,

Chris Gammell: bands and frequencies? Um, so if you have a, like, again, in the old days where you just had 2g and 3g, yeah, you, that just translates into like some frequency range you have to hit. So it's like the low band was like 824 to 960 megahertz. And that was, that included US and EU. And then the high band was like 1710 to 2170. So you would just say, okay, these are the frequencies I care about. And therefore, you know, I need like the target is minus three dB efficiency across all those frequencies. And then you don't care. It's like, okay, they can do 2g, 3g, 4g. I don't care. It doesn't affect me. Got it. Um, but with LTE now there's so much bandwidth that, uh, they can't, it's really tough to cover all that. So there's like antenna tuners, which are essentially like switches, uh, where you can like, like you think about like an antennas, uh, resonant frequency as a function of its length. So you could switch in like a longer arm or a shorter arm to change the

Pete Bevelaqua: frequency for instance. So it's almost like an old school radio where you're like actually turning the dial and it's actually moving like a slider onto something, but it's now it's doing that with

Chris Gammell: digital. Yeah. I mean, essentially, essentially. And then there's also like impedance match tuning where you put like, you might put like a series cap or switch in a shunt inductor or something.

Pete Bevelaqua: And like, that's another way to tune, but that's, yeah, that's really cool. And so when is that kind of decision made? Is that made during the antenna design phase? Like it's like, we're going to have

Chris Gammell: 20 taps or the, yeah, 20 would be a huge, that, yeah, it's not like that. It'd be like, I'm, I'm,

Pete Bevelaqua: I'm pulling many things out of my, my rear today, Pete. So just remember that.

Chris Gammell: Yeah. Again, like if you start adding a lot of complexity, like you're going to have like a lot of extra loss in there, it's going to be too complicated. You know, the big goal is like, you pay people a lot of money to keep things simple. Okay. Yeah. Yeah. That makes stuff hard is that's not good. Yeah. Um, but yeah, so you antenna design should be fully signed off before they start like going to like a proto build, for instance, like you should say, I have these switches in place to cover these bands. These are the locations I have. These are the critical points. So we're ready to go. Yeah. You don't like build a prototype or, you know, start making units and you're like, Oh, we have to add a switch. That'd be pretty sloppy. Got it. Okay. And so like in

Pete Bevelaqua: prototyping kind of stage, like what is a prototype? Is it a prototype antenna, just copper on flex PCB or is it printed onto something or is it part of a circuit board? Like what does it look like in prototype and then kind of moving up towards production? There's different ones. So yeah, the earliest

Chris Gammell: ones like you could 3d print, you know, like let's say somebody wanted to make a phone that's like a triangle or something like you could 3d print that triangles like copper tape out where the PCB is. And that's kind of your ground plane. So the ground in the PCB is also like part of your antenna. Okay. Um, so yeah, the antenna doesn't sit alone by itself. That's why you buy an antenna off digit key. For instance, it'll say like, Hey, you need a ground plane this size. Um, cause that's part of the antenna. Uh, but yeah, so you could 3d print, you know, a triangle layout, copper tape for the ground plane and then say, okay, well, I'm going to give myself eight millimeters and this direction for my antenna to keep out and just start, yeah, cutting copper tape in there and then measuring it as you go. Like that's a valid way. You could also, uh, simulate it. Um, you know, whatever you want to do.

Pete Bevelaqua: Okay. That's good. That's good to know. And then how do you start to like take other, like the other stuff in the field of, like, of not the field of view, but I guess it's the, the radiation field of view or whatever it is called. How do you, how do you deal with like a hand on a cell phone or a head on a cell phone? Like how do you deal with that kind of thing?

Chris Gammell: Um, so for, yeah, so there's a certain amount of like loss that they expect in that case, but, um, so like the carrier will have specs, like, Hey, you know, you have to radiate this much power when the phone's by itself. When you strap it to someone's head, you know, you radiate this much power and they might reduce the limit by three dB or something. But the way to test is, yeah, they just sell like, so your hand is just basically a little bit of loss, high dielectric. So you can buy like materials. It's similar. Um, yeah, you can buy a fake hand or a block, whatever, and just strap it to the product and measure the efficiency again. Okay. So, yeah, I mean, it doesn't have to be hard. You could also simulate. Yeah. Yeah. What about the, um,

Pete Bevelaqua: the shape of an antenna itself? So like I'm thinking with copper tape, at least it's like planar and very flat. Uh, you know, there's some thickness to it, but like, how does that end up impacting the, the shape of like the, not the shape, but I guess the radiation patterns out of this thing? Is it always meant to be like the same, like uni, uni directional, um, uh, radiation?

Chris Gammell: Yeah. So ideally you would want that. So, and again, the unidirectional is kind of like a donut pattern. So that would be like the lowest. So like when you buy an antenna, it says Omni. What that means is, is actually like a donut shaped pattern. There's no perfectly spherical antenna radiation patterns. They don't exist. Um, but yeah, so you look at a phone, um, so the low band, like let's say it's like 800 megahertz. A half wavelength is like six inches or whatever. You're actually, the phone itself is less than a half wavelength at the lowest cellular frequency. So I already know no matter what the antenna designer does, it doesn't matter. It's going to have low gain, low directivity, which means the pattern is going to look kind of like a, like the donut. So it doesn't even matter.

Pete Bevelaqua: Well, isn't one of the techniques of like folding antennas back on themselves and stuff though as well.

Chris Gammell: Yeah. You can meander them. Um, but you're still not going to end up with like the super directive antenna. You can't do it. Um, at the higher frequencies, you know, the, the phone, instead of being like less than a half wavelength, it's like might be two wavelengths long. In that case, you know, yeah, the pattern starts to shift and they shift in pretty predictable ways. Like, you know, I didn't work on the iPhone 10 in front of me, but I could tell you at the low band radiation pattern looks like because I know the size of it. I know like the high end of the, yeah, the spectrum where the phone might be three wavelengths long. I know it's like the radiation pattern bends back towards the display in a certain direction. And I don't know anything about how they designed it.

Pete Bevelaqua: Yeah. Okay. I think you kind of start to see the matrix for radiation patterns and such.

Chris Gammell: Yeah. Actually I interviewed at Apple and someone asked me, I was like, what's the polarization on this antenna at low band? And I hadn't worked on cell phones. I was like, well, tell me what the antenna design is. And they were like, you don't need to know. And to answer the question. And I like, I hadn't clicked till later. I was like, okay, now I know why they were asking that. Cause they know exactly what it should be. If I'd worked on this, I'd be like, Oh, okay. The polarization is this way. And the pattern goes like this. Doesn't matter like exactly what they did on the inside.

Pete Bevelaqua: I'm not sure if we'd be able to explain that on audio only, but could, could you try and explain that a little bit more?

Chris Gammell: So yeah. So like, so like antennas, well, like a phone antenna, the lowest frequency, it's fundamentally like a dipole, a halfway blank dipole. Like they want it to be, you might think it's more complicated, but it's really not. So one arm of the dipole is the whole back metal, which is like the display and the, the, the chassis, um, that forms that. And then the other half is just like a small strip. Uh, that's usually like, if a phone has a lot of metal, it's actually that metal that is part of there. Um, but there's no way to have a phone. Like if you hold it upright, there's no way that the phone is going to be horizontally polarized at the lower frequency. There's no way it has to, like the current has to flow in the long direction. Right. Automatically, you know, vertically polarized. There's no way to do it otherwise.

Pete Bevelaqua: Okay. Yeah. That's, that's good to know. That's good to know. So then, um, so you'd mentioned like, you know, you have antennas that are, uh, across multiple frequencies as well. Are they usually, so say it is all one antenna, somehow you get it all in one antenna. Does that mean that there's, there's just that single element and it is again, just a dipole that's looks good for all these

Chris Gammell: frequencies or what does, what does that look like? Yeah. So there are definitely like you can make an antenna that will cover like, for instance, 824 to 960. And then that'll be the low band. The same antenna will cover like 1710 to 2400. Like that's definitely, uh, been done and doable. Um, so, you know, there's rules in antennas. I mentioned one of them, which was like the half wavelength another rule in antennas is like more volume, the more volume you have, the more bandwidth you have. So, um, when we talk about like a thin dipole, like just two wires, that's pretty low bandwidth device, but you could really increase the bandwidth if you start making that dipole wide. Um, so just thickening up the actual, the width of that, of that, that strip you're saying. Yeah. And not just making it a wire anymore, but like a, think about it like it's a, you know, like a whole ground plane for each arm. When you start doing that, your bandwidth really gets large.

Pete Bevelaqua: Um, so yeah. So yeah. Well, why, why is that relationship there? I guess I, I don't, I can't.

Chris Gammell: Why does more bandwidth equals, I guess like fundamentally it's just, uh, if you think about like you have a very thin wire that's, you know, or two wires that form a halfway blank dipole, um, there's only like one fixed current mode that can fit on that. There's no like degrees of freedom for the current, but if you, you know, it's almost like, you know, you have thickened things up, the current has extra paths to go. The resistance drops. Well, it's the same for radiation. Like you give it extra degrees of freedom for where the current can flow and there's more modes or more frequencies can kind of fit on that structure and give rise to radiation. Oh, that's interesting.

Pete Bevelaqua: Yeah. I mean, cause at the end of the day, like you're saying it is current, it's current moving back and forth and then that causes radiation to happen. Uh, but you're saying that it would be like the equivalent of putting like multiple thin wires next to each other, right? Essentially. Yeah. And I like never thought about it like that. That's really cool. Um, so, okay. So now we've done prototyping, we've cut up copper tape, we've tried out different things. What happens then when you're like, okay, you go to production or you go to even more, you go to FCC testing. What is, how do you, how do you modify things as an antenna designer? Like, did you come in with like an X-Acto knife? You're like, nope, snip, snip, snip, snip, snip.

Chris Gammell: A lot of times. Yes. Um, so like, yeah. Um, so, okay. So once you have a prototype, if it's a mock-up, you know, from there, like you got to integrate everything. And like I said, like all the flex is like the battery, it's not a, you know, that's going to have a connector on it and all these different things. Uh, you know, you have the battery, the camera, mic flex, flex is just flexible PCB, but you know, the button, like you're going to have a button right in the middle of your

Pete Bevelaqua: antenna volume typically. You know, windows phones have a, you know, more than one button. I, so I don't know what you're talking about. So yeah. So, um, it's just, you keep going with

Chris Gammell: higher degrees of fidelity, um, with a mock-up, you know, eventually like when they build it, you know, uh, when I do the first prototype build, it's like a first form factor. It's kind of like the way the product works and all the teams have their, uh, functionality in place. So everybody could, you know, it's the first time everything comes together. You know, at that point you'll just, uh, measure the antenna exactly as I said before, where you cable it out, measure VSWR, measure the efficiency. And typically you'll find like, uh, it's lower than you expect and you start figuring out why. And that process is just like, okay, I think maybe this flex or this component here is causing me a problem. Very simple. You rip it out, you measure it again. Oh, look, there's two dB loss due to that. What can we do to mitigate it? So that might be, then you start like, okay, we need a ground point here or we need to choke this line. So a choke is just, you know, like a inductor or something on a line that will pass the low frequency and, you know, ideally block or choke the RF, uh, frequency. So if the current doesn't flow at RF, it's not going to eat the efficiency. So, you know, that's like a example of a mitigation technique. Okay. Yeah. So there's a lot of,

Pete Bevelaqua: without having to cut, you can just add something in your setting.

Chris Gammell: Correct. And so like early on, you know, you might have experience with different things and add like placeholders like, oh, we might need chokes on these lines and we're really going to need grounding here. You know, this is a risk. And so there's a few like builds where you're, uh, getting that integration. Right. And then inevitably, uh, things are changing. So at the same time, you know, like the reliability team and the product design team, they have their own specs. Like they want to drop the phone from a meter and it should, you know, like, Hey, four of them, four of them broke. And it's because we need to, now we need to thicken up this piece here. So then you work with them like, Hey, they're like, Hey, we're going to change this. And you have to like factor that in or say, okay, yeah, that's fine. No big deal. Or, okay, well that screws this up. We've got to figure out a different way. There's a lot of that. And then by the time you're at cert though, you know, you start testing cert right away. So you can figure out like, you know, what all the issues are. Um, but yeah, I mean, it's, it's basically like every day you're coming in and trying to find the problems, fix them, get ahead

Pete Bevelaqua: of it. Yeah. And it sounds like a lot of like revision tracking type of stuff as well, because things are, are migrating. Like you, are you, you, how far behind the, the leading edge of the design were you? Like, were you closer to the production side of things or closer to the design side of things when you're moving design for insurance? Yeah. Yeah. So it's a lot of work between,

Chris Gammell: you know, the initial concept to getting something ready for production. And then, yeah, we'd be like antenna engineer typically be at builds close to production, sometimes production, but they're really, they shouldn't be there at the production bill that's owned by operations team. Who's goals to figure out how to make, you know, from one production line that works, how to make 30 production lines at work and track all these things. Right. And you have

Pete Bevelaqua: a golden unit they're comparing against probably anyways, right? Yeah. Okay. Well, you keep, you keep, uh, mentioning VNAs and we alluded to it at the beginning of the episode as well, but you built your own VNA and, uh, I'm not sure if you were using it at work, but you were definitely using it. So could you go through your, uh, your, what it was real quick and why

Chris Gammell: you decided to build one? Yeah. So I worked at, you know, I worked at the antenna engineer and consumer electronics and like, uh, there's one lab I worked, everybody had antenna, uh, VNA on their desk and, you know, we come in cause it was our primary tool. And I was always looking at him. I was like this, why is it so big? Why is it so expensive? They're charged like 40, 50, $60,000. The Cal kit is like $10,000. And I never quite understood that. Cause meanwhile we're building like, you know, phones that are like $600, but you know, have much better screens and all this. And, and then like, I knew that like my phone interacts with the antenna in such a way that it can measure all the magnitude and phase of what's coming to it. Cause that's how digital communication works. Right. Yeah. And the VNA was essentially doing the same thing, although a lot more, I guess, sensitive. Right. Right. And so, yeah, it was, I was like, you know what? I was like, I bet I could build a VNA or I want to build a VNA. Actually I went to Maker Fair and there was this guy who was showing like really simple VNA designs that, you know, I went and built it first, which weren't very practical or very reliable, but that's kind of what got me started. I was like, you know what? I'm going to do this. And I didn't know anything about like microcontrollers or piece. I'd never done PCB layout and all this. So that was the basis of a talk at your hackaday thing that I gave that's online if anyone wants to see it. But I go through like the whole process and I was just like, look, if I'm going to build a product, I need to do A, B, C, and D. And I just wrote it out and it was like stuff I'd never done. Like learn how to blink an LED on a microcontroller, learn how to, you know, do PCB layout. And then like, I need to make a proto here that accomplishes these goals. And I just made a schedule and then just started knocking it out. It was actually really fun. I learned a ton and I had a much better idea.

Pete Bevelaqua: I point people to that talk. Well, I just like, I, the, the fact that you, you kept it like just saying like, well, and then I just went and figured this thing out. And I'm like, yes, that is awesome. Like you did, you just, you know, you kind of went through and you, you figured out you needed to do a thing like blinking LED, but you know, like each iterative step then was just getting you towards that end goal. But you had the goal in mind too, which is really a good start.

Chris Gammell: Yeah. Yeah. I mean, and just like being able to make a board where I put a microcontroller on there, talk to a program into flash an LED. Like when that LED blinked for the first time, I remember just being like, oh yeah, so happy. So I was like, I know how to do the next like 30 things. Cause now I'm controlling this guy. It's like, it's on. Yeah. Yeah. That's great. So, so, uh,

Pete Bevelaqua: what, what are some of the, like the, the baseline elements that are in a VNA that you had to actually design it? Was it all like buying chip sets and, and having them can do the heavy lifting or?

Chris Gammell: Uh, someone, so the, the problem, or I guess the hard part is to measure the impedance of something at RF, you're kind of have to measure like the reflected wave. So impedance and what's reflected from the antenna are the exact same thing. Um, cause like there's an equation that relates the two. So like if you have a 50 ohm line and a, uh, 60 ohm antenna, for instance, the reflection coefficient is determined. So if you measure either the reflected wave, it's the same as measuring the impedance. To get the reflected wave, you have to have a thing called a bi-directional coupler, which essentially like, you know, you're pushing energy to the antenna, but the energy that comes back is what's reflected and you have to be able to pull that out of the same line. So the bi-directional coupler, you know, basically siphons off some of that reflected energy. And to get that right over a pretty wide bandwidth is pretty tough. Um, so that was a lot of iterations where I was trying, like, you can buy couplers on Digi-Key that are cheap or make printed ones on circuit boards that kind of do the same thing. So that was, that was pretty challenging. That's probably one of the fundamental things in the VNA.

Pete Bevelaqua: That's what you're, that's like what you're paying for in a, in a good VNA kind of.

Chris Gammell: I have no idea what's in there. I've never done a tear down. You're afraid to, afraid to take apart your expensive piece of gear. Yeah. Um, so then, yeah, you have, you know, amplifiers, you have, say you have a frequency synthesizer for instance, which is another cool little, so you can just buy like a frequency synthesizer that'll work like from, you know, 10 megahertz to six gigahertz or whatever. And you just program it with MCU or you're saying, hey, I want this frequency to come out and it does. It's really cool. Yeah. That is, yeah, that's great. So the frequency synthesizer puts out the frequencies. Like when you're, want to measure a GPS for instance, you just say, hey, put out GPS frequency and then you measure the reflected wave. And, um,

Pete Bevelaqua: Hmm. Okay. So you're outputting, so you're outputting a, so you're generating a signal, 1.575, whatever it is. Whatever. Yeah.

Chris Gammell: Yeah. You have to do a sweep over whatever range, but yeah.

Pete Bevelaqua: Okay. But in, in the instant you're outputting this frequency, you have to amplify it as well. I'm guessing.

Chris Gammell: Yeah. You don't necessarily need to, but yeah, you can.

Pete Bevelaqua: Okay. Yeah. Then you push it out, but how, and then it, the coupler is what actually allows you to siphon off, like you said.

Chris Gammell: Yeah. So you put an antenna in there. Once you plug an antenna to your VNA, you automatically have reflection there. And that reflection determines.

Pete Bevelaqua: How do you discern what is reflection versus what you're actually sending out? Because it's all in the same line, right?

Chris Gammell: Yeah. So there's basically like a coupled line in there that's designed in such a way that it, um, they have a parameter for the coupler and that's happens to also be called directivity. And it measures like how much more sensitive this line picks up the forward versus the reverse, uh, traveling wave. So like a good bidirectional coupler might have a, you know, directivity of 30 dB, which means like the reflected signals, 30 dB stronger, uh, than the forward traveling wave. So, um, yeah, so a lot of it, you know, if you type bidirectional coupler into DigiKey, you'll, you can pull up some spec sheets and start looking and that's pretty much how it's spec'd out.

Pete Bevelaqua: That's pretty cool. Um, yeah. So, and then, so then the stuff that you siphon off, that is the reverse, the stuff coming back, then that just goes into ADC or what are you actually doing to actually measure that then?

Chris Gammell: Um, so that then you need to know basically the relative phase to the forward wave, because you need magnitude and phase. And so then, yeah, there was a chip that would give me, they would output like a voltage that was proportional to the magnitude of different voltage. It was proportional to phase. And then, yeah, I would just ADC those lines and get like essentially the, you know, the value for the complex, uh, reflection coefficient. And once I have that, I can immediately know the impedance.

Pete Bevelaqua: That's great.

Chris Gammell: And so, yeah, so it's fundamentally simple. It's like you're sweeping through different frequencies. You're stepping through at each step. You measure the magnitude and phase of the reflected wave, and then you get the impedance.

Pete Bevelaqua: Yeah. I mean, you make it sound simple and then you even showed how to build one and makes it sound kind of simple too. But it's like, damn, there's a lot of stuff in there.

Chris Gammell: Yeah. And then my, my big goal was to get on Kickstarter. I got it on Kickstarter. Um, uh, but yeah, the demand wasn't there. So, yeah, you know, so I think that's kind of learned why they're so expensive. One is like to get a really high bandwidth thing. Like you need a lot of switches in there, a lot of getting everything exactly right. Like it is pretty challenging. It's not like, Oh, I'll make a V&A done. Um, yeah. And then, yeah, it's just, you know, it's not like phones where you're going to sell, you know, 20 million a year, you're going to sell like 200 a year. Right. So, you know,

Pete Bevelaqua: And you're like already competing in the lower end market versus something higher margin. So,

Chris Gammell: Yeah. So yeah, ultimately I met the goal of putting on Kickstarter, offered it for sale, got a bunch of orders, which was cool, but didn't hit the target. So I decided, Hey, I got my V&A. I'm keeping it. That's great. And you still use it?

Pete Bevelaqua: Yeah, I do. Yeah. That's great. That's great. How does it compare to like a, so like, what is the frequency range of the V&A that you built? It's like 400 megahertz to 2.7 gigahertz.

Chris Gammell: So if I'm doing like, uh, you know, Bluetooth or something or cellular, like low band cellular, high band cellular, I can do that. Um, but yeah, it's just mainly in my house. It's super light, which is cool. Like it's the size of like, you know, like a big iPhone, whereas like, you know, professional V&As are so big, you're going to have to hurt your back. Yeah. Right. Right. So, yeah. Yeah.

Pete Bevelaqua: That is nice to be able to, and, and like, uh, probably bring it to a meeting and pull it out and show someone and be like, they'd be like, wait, what is that? Yeah. That's great. Uh, so, I mean, you're, you're doing consumer level stuff now. I mean, you'd like you mentioned, there's, um, you know, V&As are a big tool there. Are there other tools that you find yourself using on a daily

Chris Gammell: basis that people should know about? Um, I mean, besides rework equipment, like, you know, if you're an antenna engineer, you need to be able to solder O2O1s and such for your impedance matching. Um, but yeah, so if you have a anechoic chamber, you can measure the efficiency. If you have a VNA, you can measure your impedance. And also if you have multi-antenne systems, you can measure the isolation, which is like, if you put an energy into one antenna, how much does the other antenna absorb? Okay. That's another important parameter for multi-antenne systems. But yeah, VNA and, uh, a chamber is fundamentally all you need. Uh, you could also add simulation tools if you want.

Pete Bevelaqua: Um, how big are the chambers that you would use on just testing versus like a FCC certification type

Chris Gammell: thing? Um, yeah, so they can be pretty small. Like there's a company, Satomo that makes one that's only about a nine foot cube and that one, uh, so that's a smaller one. It's, but it will do cellular. Um, so the size of the chamber you need is really a function of the wavelength again. So if you're doing like 60 gigahertz millimeter wave stuff, you might need like a chamber that could fit on a desk. It's much smaller. Um, but yeah, the ones that consumer typically use are, you know, nine to 13 feet on a side for a cube. Yeah. Like room sized. Yeah. FCC. Yeah. They get really big, like a five meter chambers and that's just cause they measure super low frequencies. Like you got to measure the radiated emissions that, you know, two megahertz. Yeah. Yeah. So I always figured that

Pete Bevelaqua: was because they also drive like bigger things that they might have like larger devices in there as well, but I guess that's, yeah, that's pretty cool. Well, Pete, what else should we know about you and antenna theory and, uh, you know, your background? Is there anything else we missed? Um, geez, I don't know your whole life just, you know, like condensed down to an hour,

Chris Gammell: you know? Yeah. I'm working on, uh, putting a rocket on a balloon, lighting a rocket when the balloons up. So I made a raspberry pie that, uh, battery powered raspberry pie that just waits for a certain amount of time and then just, uh, turns on a switch, which fires a little igniter, which I'm going to put on a rocket that's on a balloon. That's a project I'm working on. Okay. And the

Pete Bevelaqua: rocket is going just up further or what's the deal? Yeah. Okay. So yeah. Like, I don't understand why.

Chris Gammell: So the, like the biggest thing in rockets is, uh, even bigger than gravity is wind resistance. And it's like, when you get to a hundred thousand feet, it's like less than a thousandth, I think, the air density. And what's that in dB? 30 dB. There you go. Yeah. That's a, that's a good catch. Um, yeah. So I had this idea and it turns out other people have had the idea and done it, but, um, so I'm kind of doing something that's been done before, but yeah, no reason not to do it though. That's cool. Yeah. So I still, so like little things, like I put a GoPro on the balloon and it has to work. It's like minus 40 degrees in there. So I make sure I run my GoPro in my freezer and figure out how to insulate it. So I literally have like GoPro in my freezer at home and I'm like recording to make sure what type of insulation to keep it working longer. That's great. I do a lot

Pete Bevelaqua: of stupid stuff like that. No, it's super fun though. It's super fun. And like, are you just trying to get the rocket higher to get like more curvature out of a picture kind of thing? Um, yeah, there's not a

Chris Gammell: super big goal right now. It's just like, you know, I've wanted to do the balloon experiment, which people do where you like, you can take a balloon up to a hundred thousand feet and then it pops, a parachute goes and you go and get it. Yeah. Yeah. I want to do that. And then the rocket is just, I got into rocketry as well. It's kind of fun. Yeah. Just combine the two.

Pete Bevelaqua: That's great. That's great. And you, plus, you know, the antennas are going to be really good on those things. Yeah. Fantastic. Well, Pete, this has been great. Where can people find you and more

Chris Gammell: about you online? Um, go to antenna theory.com. So everybody, you know, if you're like, Hey, what you said here wasn't right, or don't agree on more information, feel free to ping me by emails on the website. But yeah, this is my two cents on antenna engineering. It's my take based on my experiences. That's great. Thanks for having me. You know, it's fun. Yeah. Like chatting about

Pete Bevelaqua: antennas. Yeah. Well, definitely. Uh, I'm probably going to give you a call sometime soon with lots of questions to bend your ear about it. So cool. Thanks Pete. All right. Thank you. Once again, we'd like to thank our sponsor Roden Schwartz, a leading manufacturer of value instruments designed to help you maximize your bench's performance for everyday applications. They just announced an industry first complete solutions with all the upgrades upfront for one price. Now through December 31st, save up to $10,000 on Roden Schwartz solution packages that come with fully loaded test and measurement instruments right from the start. When you invest in Roden Schwartz products, you get the highest quality engineering, plus all the bandwidth channels, inputs, memory interfaces, and signal generation you'll ever need. Learn more about Roden Schwartz value instruments and this limited time promotion at askanengineer.us. That's askanengineer.us. administered administered administered administered administered administered administered administered

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