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Design007-Apr2020

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APRIL 2020 I DESIGN007 MAGAZINE 67 sort of stackup? Then, we have my antenna col- league, saying, "We are putting the antenna on the PCB, so we don't want too thin of a sub- strate because we don't want to create some- thing that's too lossy or capacitive." You need to understand the materials you are using, and you need to understand the people who are us- ing those materials and how that it is all going to come together. Shaughnessy: And it's a regular FR-4 board? Marshall: That is why we have had this con- versation already. One of the questions often posed is, "What's your board designed with?" If somebody says to me FR-4, I say, "That's nice;" there are thousands of them, so you have to be quite specific. Again, when looking at materials, if there is particular local support from the laminate vendor, it can help you so much. They know their material, and they can give you lots of helpful advice, which can save you a lot of pain later. Holden: Will this be completed by next year at this time? Marshall: I hope so. Shaughnessy: It has been great talking with you, Richard. Thank you. Marshall: Thank you, Andy and Happy. DESIGN007 You need to understand the materials you are using, and you need to understand the people who are using those materials and how that it is all going to come together. Shaughnessy: And they reached you through one of these incubators? Marshall: It was through one of the startup meetups in London. We're probably the major- ity of the way through the journey, but there's been some interesting stuff on the way, which is why—in the end—you have that "throw- away" conversation. Listening to some of the conversations led to some points that will hopefully help other designers, particularly those who are not so familiar with radio. I've spent a large portion of my career, not as a ra- dio engineer, but usually on the baseband en- gineer butting up to go to the RF side. Holden: Are there particular radio frequencies that you're restricted to for an application like this? Marshall: This one is classic licensed spectrum cellular radio. The current product is 2G/3G, but it would not be that difficult then to take it onto 5G frequencies. If you look at them, they're all pretty much the same. The big dis- tinction for 5G is you come down to 700 MHz instead of 850 MHz. You're operating from 700 MHz to over 900 MHz, and then you work from about 1,750 MHz to over 2,100 MHz, so there is some antenna tweaking to do. Shaughnessy: Is that UHF or VHF? Marshall: It's all UHF. We have been involved with things like Bluetooth and some of the high-frequency stuff like DSRC up at 5.9 GHz. One of the other things we'll be talking about is picking a PCB laminate. Don't tell me what Dk is at 100 megahertz; I want to know what it is all the way across the whole frequency of operation. Holden: As you brought up earlier, you are go- ing to visit your fabricator and bring them in early in the project. Marshall: In this particular case, that was abso- lutely essential, we had a number of long con- versations with the fabricator, such as what

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