77GHz Radar with FR4 board?

We once did a board with mixed FR4 and microwave laminate layers. They looked like potato chips. I could lay one on my desk and give it a twirl and it would spin for a full minute.

Actually, that didn't work very well so we did the next gen all FR4.

Is something intermediate-cost stuff better than FR4 at speed? Polyamide maybe?

I can only evaluate to 20 GHz with my TDR gear, but short runs on FR4 look pretty good. On longer runs, the killer is not so much dielectric loss, but the horrible black oxide treatment of the traces which aids adhesion to epoxy. Peel one up. It's disgusting. Maybe somebody can fab FR4 boards with smoother copper.

What the hell kind of cost-sensitive semiconductor does anything in

People are making shockingly cheap radar and lidar chips for cars. The markets are enormous. Joerg probably needs to make the patch antenna or something like that.

I have some Megtron 5, R5775 Dk

One cute trick the super-high frequency guys use is "suspended substrate." Route out regions of the board from below, almost up to the layer 1 traces. That makes the dielectric mostly air. I've asked pcb houses if they can do that, and they all said "sure."

part of the issue isn't just the loss, but also the tolerance or variation of dielectric constant from unit to unit. m

Air is pretty consistent.

Yup, the antenna. Discrete hardware is also cheap. I made a TDR for a client that is in the 100psec range and the RF section is around a buck in cost. Even in low 1k qties you can get RF transistors with an ft around 80GHz for 15 cents.

Yes, if we need expensive material we'll shop around. FR4 would be best though if it somehow suffices.

That is a good method but only works if you do not need a ground plane underneath the antenna. We probably will but not sure yet.

Depends on where. In some cities people trust air only when they can see it.

Is there a metal baseplate or box? That would become the ground plane.

The cute little Murata dc/dc converter, discussed here, has an internal cavity that was apparently routed before the board was laminated and plated. There's a ferrite toroid rattling around inside. And it's cheap, so that must be easy in volume.

An air cavity hogged out of one internal layer would be interesting. It's not exactly multilayer or suspended substrate: we could invent a new name if there isn't one already.

We have 65 terms for various kinds of fog.

That could be plan B. Not so nice but possible.

Ok, but rattling is not so good. That can fail when installed on a vehicle.

That looks like an ant hotel :-)

Well, don't put a toroid in the cavity on your version.

It does look sort of like a ZZ-band waveguide. Maybe one could fab a steerable slot antenna array like this. Squirt the RF out slots on the side of the board.

Maybe the toroid likes fresh air? For 2 pF+4200 volts isolation I'll tolerate a little quirkiness.

(I'm prepping for a customer visit. Jerks. Makes me crabby.)

That is pretty good. For most of my apps it would depend on what the spec'd working voltage is.

I hope it goes well. So far I have been lucky, only very few customers over my career that I didn't like.

For some reason, people in the semiconductor business are usually awful. I think Shockley established the mores of Silicon Valley.

You're getting close. To listen to Rogers tell it, at 77GHz the skin effect loss due to the copper surface roughness is overwhelming, something like 2 .2dB per inch. They have a super smooth copper laminate and application pro cess that improves this considerably- just exactly how much I seem to have missed. So they do have a product with this super surface smoothness lamina ted onto an FR4 substrate to make it more economically feasible in cost con scious applications. The other stuff with dielectric loss, radiation and le akage losses remains acceptable.

Bardeen and Brattain discovered the point-contact bipolar transistor. Shockley tried to take credit for it.

I had lunch with Brattain when I was a kid. Nice old guy.