On 2019-04-02 08:06, John Larkin wrote:> On Tue, 2 Apr 2019 06:55:01 -0700 (PDT), makolber@yahoo.com wrote: > >> On Tuesday, April 2, 2019 at 9:20:55 AM UTC-4, John Larkin wrote: >>> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> Attention, non-political post! >>>> >>>> Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive >>>> Radar purposes? If so, which kind/vendor? >>> >> 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. >Depends on where. In some cities people trust air only when they can see it. -- Regards, Joerg http://www.analogconsultants.com/
77GHz Radar with FR4 board?
Started by ●April 1, 2019
Reply by ●April 2, 20192019-04-02
Reply by ●April 2, 20192019-04-02
On 2019-04-02 06:20, John Larkin wrote:> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> > wrote: > >> Attention, non-political post! >> >> Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive >> Radar purposes? If so, which kind/vendor? >> >> I know, I know, this ain't kosher but it's a cost-sensitive case and >> this one does not need to reach top-notch RF performance. And I promise >> not to try that on phenolic :-) > > 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." >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. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●April 2, 20192019-04-02
On Tue, 02 Apr 2019 09:39:32 -0700, Joerg <news@analogconsultants.com> wrote:>On 2019-04-02 06:20, John Larkin wrote: >> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> Attention, non-political post! >>> >>> Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive >>> Radar purposes? If so, which kind/vendor? >>> >>> I know, I know, this ain't kosher but it's a cost-sensitive case and >>> this one does not need to reach top-notch RF performance. And I promise >>> not to try that on phenolic :-) >> >> 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." >> > >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.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. https://www.dropbox.com/s/l8xpzmwsg8lq287/DSC03456.JPG?dl=0 -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 2, 20192019-04-02
On Tue, 02 Apr 2019 09:39:49 -0700, Joerg <news@analogconsultants.com> wrote:>On 2019-04-02 08:06, John Larkin wrote: >> On Tue, 2 Apr 2019 06:55:01 -0700 (PDT), makolber@yahoo.com wrote: >> >>> On Tuesday, April 2, 2019 at 9:20:55 AM UTC-4, John Larkin wrote: >>>> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> >>>> wrote: >>>> >>>>> Attention, non-political post! >>>>> >>>>> Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive >>>>> Radar purposes? If so, which kind/vendor? >>>> >>> 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. >> > >Depends on where. In some cities people trust air only when they can see it.We have 65 terms for various kinds of fog. https://www.dropbox.com/s/b441bf7y5rfj1kh/Fog_p2.JPG?dl=0 https://www.dropbox.com/s/blnr8piesa35yi1/Fog-out.JPG?dl=0 -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 2, 20192019-04-02
On 2019-04-02 10:59, John Larkin wrote:> On Tue, 02 Apr 2019 09:39:32 -0700, Joerg <news@analogconsultants.com> > wrote: > >> On 2019-04-02 06:20, John Larkin wrote: >>> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> Attention, non-political post! >>>> >>>> Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive >>>> Radar purposes? If so, which kind/vendor? >>>> >>>> I know, I know, this ain't kosher but it's a cost-sensitive case and >>>> this one does not need to reach top-notch RF performance. And I promise >>>> not to try that on phenolic :-) >>> >>> 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." >>> >> >> 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. > > Is there a metal baseplate or box? That would become the ground plane. >That could be plan B. Not so nice but possible.> 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. >Ok, but rattling is not so good. That can fail when installed on a vehicle.> 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. > > https://www.dropbox.com/s/l8xpzmwsg8lq287/DSC03456.JPG?dl=0 >That looks like an ant hotel :-) -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●April 2, 20192019-04-02
On Tue, 02 Apr 2019 11:17:15 -0700, Joerg <news@analogconsultants.com> wrote:>On 2019-04-02 10:59, John Larkin wrote: >> On Tue, 02 Apr 2019 09:39:32 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2019-04-02 06:20, John Larkin wrote: >>>> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> >>>> wrote: >>>> >>>>> Attention, non-political post! >>>>> >>>>> Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive >>>>> Radar purposes? If so, which kind/vendor? >>>>> >>>>> I know, I know, this ain't kosher but it's a cost-sensitive case and >>>>> this one does not need to reach top-notch RF performance. And I promise >>>>> not to try that on phenolic :-) >>>> >>>> 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." >>>> >>> >>> 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. >> >> Is there a metal baseplate or box? That would become the ground plane. >> > >That could be plan B. Not so nice but possible. > > >> 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. >> > >Ok, but rattling is not so good. That can fail when installed on a vehicle.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.> > >> 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. >> >> https://www.dropbox.com/s/l8xpzmwsg8lq287/DSC03456.JPG?dl=0 >> > >That looks like an ant hotel :-)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.) -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 2, 20192019-04-02
On 2019-04-02 12:38, John Larkin wrote:> On Tue, 02 Apr 2019 11:17:15 -0700, Joerg <news@analogconsultants.com> > wrote: > >> On 2019-04-02 10:59, John Larkin wrote:[...]>>> 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. >>> >>> https://www.dropbox.com/s/l8xpzmwsg8lq287/DSC03456.JPG?dl=0 >>> >> >> That looks like an ant hotel :-) > > Maybe the toroid likes fresh air? For 2 pF+4200 volts isolation I'll > tolerate a little quirkiness. >That is pretty good. For most of my apps it would depend on what the spec'd working voltage is.> (I'm prepping for a customer visit. Jerks. Makes me crabby.) >I hope it goes well. So far I have been lucky, only very few customers over my career that I didn't like. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●April 2, 20192019-04-02
On Tue, 02 Apr 2019 13:25:51 -0700, Joerg <news@analogconsultants.com> wrote:>On 2019-04-02 12:38, John Larkin wrote: >> On Tue, 02 Apr 2019 11:17:15 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2019-04-02 10:59, John Larkin wrote: > >[...] > > >>>> 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. >>>> >>>> https://www.dropbox.com/s/l8xpzmwsg8lq287/DSC03456.JPG?dl=0 >>>> >>> >>> That looks like an ant hotel :-) >> >> Maybe the toroid likes fresh air? For 2 pF+4200 volts isolation I'll >> tolerate a little quirkiness. >> > >That is pretty good. For most of my apps it would depend on what the >spec'd working voltage is. > > >> (I'm prepping for a customer visit. Jerks. Makes me crabby.) >> > >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. https://en.wikipedia.org/wiki/Shockley_Semiconductor_Laboratory https://en.wikipedia.org/wiki/Traitorous_eight -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 2, 20192019-04-02
On Monday, April 1, 2019 at 11:55:53 AM UTC-4, John Larkin wrote:> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> > wrote: > > >Attention, non-political post! > > > >Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive > >Radar purposes? If so, which kind/vendor? > > > >I know, I know, this ain't kosher but it's a cost-sensitive case and > >this one does not need to reach top-notch RF performance. And I promise > >not to try that on phenolic :-) > > 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. > > https://www.dropbox.com/s/rym97ts13dt4qp5/T420_Amoeba.jpg?dl=0 > > Actually, that didn't work very well so we did the next gen all FR4. > > https://www.dropbox.com/s/v9byymfy6ijh64g/T400_wiggles.JPG?dl=0 > > 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.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 process that improves this considerably- just exactly how much I seem to have missed. So they do have a product with this super surface smoothness laminated onto an FR4 substrate to make it more economically feasible in cost conscious applications. The other stuff with dielectric loss, radiation and leakage losses remains acceptable.> > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
Reply by ●April 4, 20192019-04-04
John Larkin wrote:> On Tue, 2 Apr 2019 06:55:01 -0700 (PDT), makolber@yahoo.com wrote: > >> On Tuesday, April 2, 2019 at 9:20:55 AM UTC-4, John Larkin wrote: >>> On Mon, 01 Apr 2019 07:42:42 -0700, Joerg <news@analogconsultants.com> >>> wrote: >>> >>>> Attention, non-political post! >>>> >>>> Has anyone used FR4 without a Rogers 3003 top layer for 77GHz automotive >>>> Radar purposes? If so, which kind/vendor? >>> >> 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. > >Maybe, but what about the mechanical routing?
