Joerg wrote:> On 2019-04-02 01:01, Robert Baer wrote: >> Joerg 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 :-) >>> >> I have some Megtron 5, R5775 Dk <=3.5 @1GHz, Dg<=0.005 @1GHz; 18x24 >> sheets 0.0366 double sided. >> Withstands 204C for hours (do not know how long); 185C without a peep. >> Megtron 5 was superior to the Rogers stuff at that time (5yrs ago). >> >> Panasonic Megtron 6 is current, and is VERY competitive with the >> current Rogers stuff (seems a number of people still dislike the Rogers). >> > > Yes, if we need expensive material we'll shop around. FR4 would be best > though if it somehow suffices. >My point was: The Megtron 5 technology is about 5 years old, and was not expensive WRT FR4 then, and i have some. And, unlike some suppliers, i do not demand a minimum qty of 20. Package weight, 1 PCB, 5 lbs; I use the very thick cardboard like that used for pumpkins or water heaters for rigidity.
77GHz Radar with FR4 board?
Started by ●April 1, 2019
Reply by ●April 4, 20192019-04-04
Reply by ●April 4, 20192019-04-04
John Larkin wrote:> 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 > > > >Shockley did not invent the transistor; it was patented in the early 1930's. Actually TWO patents, and they were FETs!
Reply by ●April 4, 20192019-04-04
bloggs.fredbloggs.fred@gmail.com wrote:> 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.* Smoothness lies in the beholder, and the app. Remember, that smooth copper top has a bottom/back side that has as much, if not more effect on traveling waves/reflections. Seems that a lot of the effort for better RF transmission, is to have precise, controlled and refined glass weave underneath; then add a smooth surface...> >> >> >> -- >> >> John Larkin Highland Technology, Inc >> >> lunatic fringe electronics >
Reply by ●April 4, 20192019-04-04
On Thu, 4 Apr 2019 19:28:10 -0800, Robert Baer <robertbaer@localnet.com> wrote:>John Larkin wrote: >> 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 >> >> >> >> > Shockley did not invent the transistor; it was patented in the early >1930's. > Actually TWO patents, and they were FETs!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. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●April 5, 20192019-04-05
On Thu, 4 Apr 2019 19:37:01 -0800, Robert Baer <robertbaer@localnet.com> wrote:>bloggs.fredbloggs.fred@gmail.com wrote: >> 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.>* Smoothness lies in the beholder, and the app.Or is measured in micro-inches RMS.> Remember, that smooth copper top has a bottom/back side that has as >much, if not more effect on traveling waves/reflections.Most of the energy in a microstrip is propagated on the underside, where the dielectric constant is higher than air. And regular FR4 boards have an ugly adhesion treatment on the underside that adds massive skin losses. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 5, 20192019-04-05
On 2019-04-05 13:04, John Larkin wrote:> On Thu, 4 Apr 2019 19:37:01 -0800, Robert Baer > <robertbaer@localnet.com> wrote: > >> bloggs.fredbloggs.fred@gmail.com wrote: >>> 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. > >> * Smoothness lies in the beholder, and the app. > > Or is measured in micro-inches RMS. > >> Remember, that smooth copper top has a bottom/back side that has as >> much, if not more effect on traveling waves/reflections. > > Most of the energy in a microstrip is propagated on the underside, > where the dielectric constant is higher than air. And regular FR4 > boards have an ugly adhesion treatment on the underside that adds > massive skin losses. >The antenna traces would, of course, be up to. However, when the FR4 underneath them causes a substantial pro delay delta the antenna tuning might get out of whack. -- Regards, Joerg http://www.analogconsultants.com/
Reply by ●April 5, 20192019-04-05
On 2019-04-04 20:20, Robert Baer wrote:> Joerg wrote: >> On 2019-04-02 01:01, Robert Baer wrote: >>> Joerg 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 :-) >>>> >>> I have some Megtron 5, R5775 Dk <=3.5 @1GHz, Dg<=0.005 @1GHz; 18x24 >>> sheets 0.0366 double sided. >>> Withstands 204C for hours (do not know how long); 185C without a >>> peep. >>> Megtron 5 was superior to the Rogers stuff at that time (5yrs ago). >>> >>> Panasonic Megtron 6 is current, and is VERY competitive with the >>> current Rogers stuff (seems a number of people still dislike the >>> Rogers). >>> >> >> Yes, if we need expensive material we'll shop around. FR4 would be >> best though if it somehow suffices. >> > My point was: > The Megtron 5 technology is about 5 years old, and was not expensive > WRT FR4 then, and i have some. > And, unlike some suppliers, i do not demand a minimum qty of 20.If this project flies we'd have to make half a bazillion.> Package weight, 1 PCB, 5 lbs;5lbs? Yikes!> ... I use the very thick cardboard like > that used for pumpkins or water heaters for rigidity. >-- Regards, Joerg http://www.analogconsultants.com/
Reply by ●April 5, 20192019-04-05
On Fri, 05 Apr 2019 13:20:41 -0700, Joerg <news@analogconsultants.com> wrote:>On 2019-04-05 13:04, John Larkin wrote: >> On Thu, 4 Apr 2019 19:37:01 -0800, Robert Baer >> <robertbaer@localnet.com> wrote: >> >>> bloggs.fredbloggs.fred@gmail.com wrote: >>>> 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. >> >>> * Smoothness lies in the beholder, and the app. >> >> Or is measured in micro-inches RMS. >> >>> Remember, that smooth copper top has a bottom/back side that has as >>> much, if not more effect on traveling waves/reflections. >> >> Most of the energy in a microstrip is propagated on the underside, >> where the dielectric constant is higher than air. And regular FR4 >> boards have an ugly adhesion treatment on the underside that adds >> massive skin losses. >> > >The antenna traces would, of course, be up to. However, when the FR4 >underneath them causes a substantial pro delay delta the antenna tuning >might get out of whack.Which is why it would be fun to mill out most of the FR4 from underneath. But the underside copper should be smooth. Cutting away FR4 would also help equalize the prop delay dispersion inherent to microstrip, although that could be tuned out in a narrowband antenna. A lot depends on whether you can give up some noise figure to make the board cheaper. Avoid hitting cars and not worry about bicycles and baby buggies maybe. That Murata dc/dc appears to be milled and then laminated and plated. So maybe one could fab the antenna as a very thin low-loss board, maybe even kapton flex, and then glue that to some cheap FR4 board that has a cavity slot, to make suspended substrate with farside ground plane. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●April 5, 20192019-04-05
fredag den 5. april 2019 kl. 22.55.45 UTC+2 skrev John Larkin:> On Fri, 05 Apr 2019 13:20:41 -0700, Joerg <news@analogconsultants.com> > wrote: > > >On 2019-04-05 13:04, John Larkin wrote: > >> On Thu, 4 Apr 2019 19:37:01 -0800, Robert Baer > >> <robertbaer@localnet.com> wrote: > >> > >>> bloggs.fredbloggs.fred@gmail.com wrote: > >>>> 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. > >> > >>> * Smoothness lies in the beholder, and the app. > >> > >> Or is measured in micro-inches RMS. > >> > >>> Remember, that smooth copper top has a bottom/back side that has as > >>> much, if not more effect on traveling waves/reflections. > >> > >> Most of the energy in a microstrip is propagated on the underside, > >> where the dielectric constant is higher than air. And regular FR4 > >> boards have an ugly adhesion treatment on the underside that adds > >> massive skin losses. > >> > > > >The antenna traces would, of course, be up to. However, when the FR4 > >underneath them causes a substantial pro delay delta the antenna tuning > >might get out of whack. > > Which is why it would be fun to mill out most of the FR4 from > underneath. But the underside copper should be smooth. > > Cutting away FR4 would also help equalize the prop delay dispersion > inherent to microstrip, although that could be tuned out in a > narrowband antenna. > > A lot depends on whether you can give up some noise figure to make the > board cheaper. Avoid hitting cars and not worry about bicycles and > baby buggies maybe. > > That Murata dc/dc appears to be milled and then laminated and plated. > So maybe one could fab the antenna as a very thin low-loss board, > maybe even kapton flex, and then glue that to some cheap FR4 board > that has a cavity slot, to make suspended substrate with farside > ground plane.maybe just a fr4 frame you can get flex/fr4 combined http://www.printedboardassembly.com/photo/pl19132516-rigid_flex_combined_pcb_multilayer_printed_board_polyimide_material_lead_free_hasl_surface_finishing_ce_rohs_standard.jpg
Reply by ●April 5, 20192019-04-05
On 2019-04-05 14:36, Lasse Langwadt Christensen wrote:> fredag den 5. april 2019 kl. 22.55.45 UTC+2 skrev John Larkin: >> On Fri, 05 Apr 2019 13:20:41 -0700, Joerg <news@analogconsultants.com> >> wrote: >> >>> On 2019-04-05 13:04, John Larkin wrote: >>>> On Thu, 4 Apr 2019 19:37:01 -0800, Robert Baer >>>> <robertbaer@localnet.com> wrote: >>>> >>>>> bloggs.fredbloggs.fred@gmail.com wrote: >>>>>> 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. >>>> >>>>> * Smoothness lies in the beholder, and the app. >>>> >>>> Or is measured in micro-inches RMS. >>>> >>>>> Remember, that smooth copper top has a bottom/back side that has as >>>>> much, if not more effect on traveling waves/reflections. >>>> >>>> Most of the energy in a microstrip is propagated on the underside, >>>> where the dielectric constant is higher than air. And regular FR4 >>>> boards have an ugly adhesion treatment on the underside that adds >>>> massive skin losses. >>>> >>> >>> The antenna traces would, of course, be up to. However, when the FR4 >>> underneath them causes a substantial pro delay delta the antenna tuning >>> might get out of whack. >> >> Which is why it would be fun to mill out most of the FR4 from >> underneath. But the underside copper should be smooth. >> >> Cutting away FR4 would also help equalize the prop delay dispersion >> inherent to microstrip, although that could be tuned out in a >> narrowband antenna. >>This is going to be a wideband app, several GHz BW though at 77GHz that's still less than 5%.>> A lot depends on whether you can give up some noise figure to make the >> board cheaper. Avoid hitting cars and not worry about bicycles and >> baby buggies maybe.As a cyclist I must object! :-)>> >> That Murata dc/dc appears to be milled and then laminated and plated. >> So maybe one could fab the antenna as a very thin low-loss board, >> maybe even kapton flex, and then glue that to some cheap FR4 board >> that has a cavity slot, to make suspended substrate with farside >> ground plane. > > maybe just a fr4 frame you can get flex/fr4 combined > > http://www.printedboardassembly.com/photo/pl19132516-rigid_flex_combined_pcb_multilayer_printed_board_polyimide_material_lead_free_hasl_surface_finishing_ce_rohs_standard.jpg >Yes, flex is a nice method but it does at substantial cost. -- Regards, Joerg http://www.analogconsultants.com/
