RF construction technique in microwave region

[tkamiya]

My past experience is 2GHz and lower.

I am starting to get into much higher frequencies.  Commercially made products are all made on PC boards with microstrip lines and distributed elements such as rat race mixers and impedance transition sections.  I really don't want to get into making PC boards.

Would it be possible to use dead-bug style constructions?  Say, use regular PC board un-etched.  For really close connections, use piece of wire and anything longer, I also have RG405 semi-rigid coax which I intend to solder outer conductor to foil on PC.  What frequency would this type of construction begin to fail? 

I am not sure if this is feasible, but when I was back in Japan in 70s and 80s, I used to see a pre-etched PC board striplines and mixers that can be glued onto foil side of PC board sub-strait.  I wonder if I can make and order abunch of these and make microstrip lined board on the fly?

I am aiming for 20GHz.  If above is not feasible, what construction method would I use?

How do you breadboard on frequencies this high???  Surely one does not go straight to ordering a pc board, right??

[TheUnnamedNewbie]

How do you breadboard on frequencies this high???  Surely one does not go straight to ordering a pc board, right??

Simulation, simulation, simulation. Experience. Modeling. And often, yes, we do actually go for a few PCB runs.

The good news is that because you really, really need to simulate at these frequencies, manufacturers tend to have better models available.

You can't really breadboard. There are systems (look for X-Microwave) that allow you some block-based prototyping, but in the end the frequencies are just too high, parasitics matter too much. Often boards would be designed in such a way that we can actually test seperate pieces if needed.

[Wolfgang]

My past experience is 2GHz and lower.

I am starting to get into much higher frequencies.  Commercially made products are all made on PC boards with microstrip lines and distributed elements such as rat race mixers and impedance transition sections.  I really don't want to get into making PC boards.

Would it be possible to use dead-bug style constructions?  Say, use regular PC board un-etched.  For really close connections, use piece of wire and anything longer, I also have RG405 semi-rigid coax which I intend to solder outer conductor to foil on PC.  What frequency would this type of construction begin to fail? 

I am not sure if this is feasible, but when I was back in Japan in 70s and 80s, I used to see a pre-etched PC board striplines and mixers that can be glued onto foil side of PC board sub-strait.  I wonder if I can make and order abunch of these and make microstrip lined board on the fly?

I am aiming for 20GHz.  If above is not feasible, what construction method would I use?

How do you breadboard on frequencies this high???  Surely one does not go straight to ordering a pc board, right??

Hi,

Its possible to make "quasi-stripline" circuits (using strips of copperclad FR4 as transmission lines) up to maybe 2GHz and a little above, but thats about it if you want something reproducible. The PCB becomes part of the circuit, there is no elegant way around that.

Dead bug at several GHz ? Not really. Some freaks do it in amateur radio (LY3LP), but its not repeatable and certainly inept for high quality designs.

At 20GHz, you dont breadboard at all. What you do is model all this properly with an EM simulator, with a circuit simulator and then optimize your design virtually. You make prototypes, but with *real* materials, *real* shielded boxes, *real* connectors, and so on. If your simulation was good, you should be not so far off.

Caveat: You need expensive equipment to fiddle around at 20GHz (A spectrum analyzer, a VNA, cal kits, RF generators, power meters, ...). When buying new, say to 40GHz (so you can see at least the first harmonic of your signal), you end up with over 100k€ for Keysight stuff).

[mc172]

I really don't want to get into making PC boards.

Why not? If you have got access to a PCB milling machine, you can design something in the morning and have it built by the time you go home, and have an idea of whether it's going to work or not.

The construction technique really is poke around with a very thin piece of plastic or a ferrite bead on a stick and then spin another board!

[tkamiya]

This is strictly a hobby endeavor.  So repeatability is not really an issue.  Equipment wise, I have 26.5GHz SpecAn and 8GHz SweepGen.  I'm working on 20GHz source as well.

I never thought about milling a PCB.  I guess it's an option.  I just don't want to etch my own board or farm it out and wait a month - as I said, for just a one off thing.

[coppercone2]

for one sided simple shit you can etch with a sponge, but I can see your aversion to the photo resist,

my printer received a BEATING for its transgressions against transparencies.

[coppercone2]

I wish someone would do experiments and find a known good printer that works with transparencies. I had everything from shrinkage, it sliding through without printing anything and making a terrible noise, partially printing and sliding through to make a terrible noise, crinkling up inside, and much more. Sometimes when it finally came out I was doing a happy dance. It's one of those random things. Sometimes it works great first try but sometimes your ready to cry. I swear its like the most unpredictable tool I have. Almost nothing else I own fucks off that bad for no reason.

One thing I learned is that you should wipe down your transparency sheets with 50% alcohol 50% distilled water before putting them in the printer, and let them dry well. It seems that it prevents large patches of ground plane flaking off.  I think a layer of plasticizer leaches out of them and forms on the surface and prevents proper toner adhesion. Also clean the printer tray real good and vacuum the inside of the printer while brushing it.

But still its a fucking troll.

I swear a good printer is valuable. I don't know what it is but sometimes you get these evil printers. I used to work a real crappy job dealing with lots of printers and there were a few demonic ones that kept fucking up despite increased maintenance, and they were all from the same series (like 15 different big ass expensive office printers). Someone thought to give them 'cute' network names too. Cute my ass. Rose. YEA FUCKING RIGHT. More like Rosemarie's baby. They had some kind of systemic problems. The implementation of the design was somehow corrupted. I never figured out how they could get so many different problems occurring in the same model. Both electrical and mechanical. jams, OS errors, door sensors not working, network errors, etc. I had to zoolander those mother fuckers daily to make sure operation could proceed. Open all the doors, close all the doors. Remove the paper from the tray, put the paper back in the tray, adjust the tray, put slightly less paper in the tray (there were magic amounts it sometimes wanted), fiddle with the doors, reset it.. but so expensive its worth it for a corporation to dedicate a low level employees time to 'dither' it. I think for a period of time someone figured out it worked more reliably when it had some weird paper size in one of the drawers.. paper that was never used. I think I was told something like 'leave the drawer alone, its been working since we did that'.

They also emit black carbon powder in addition to the rage they induce. I swear their tools of the devil.

[radiogeek381]

20GHz is pretty ambitious, though I've done a few things at 10GHz without fancy test equipment.  It helps that there were other folks around doing similar things.

For example, I've built two 10GHz transverters from surplus building blocks. The commercial mixers were found at swap meets, now Ebay has lots of them.  Those rigs used rather expensive microwave sources for the LO that required 24V and lots of tender care, but now there are credible alternatives that use cheap mmics and micro-strip filters to multiply up from a 1GHz synthesizer.  The preamps were taken from surplus downconverters.

But these radios were built entirely with discrete building blocks and semirigid coax. (Even the plumbing was surplus.)

My current 10GHz transverter was built from a kit.

Most of the transverters I've built, both from kits and from scratch were done without a spectrum analyzer and certainly without a network analyzer.  I had a power meter (HP 432A) and a sweeper.  That's it.  With those two tools you can line up filters, test out amplifiers, and do some rudimentary testing. 

Today you can build a useful power meter from parts you have around the house (if you live at Digikey .  (See http://www.w1ghz.org/new/portable_powermeter.pdf.)

The last transverter build was helped along with a 1970's vintage spectrum analyzer, but it wasn't absolutely necessary.

As for simulation -- certainly no "for hire" designs should rely on "cut-and-try" and if you're doing this for a living you should be using simulation and analysis tools. But the notion that simulation is the only path to success for "one off" or hobby devices is not well supported.  Building block approaches work just fine, and between Ebay finds and stuff from catalogs you can build some pretty capable systems without spending a whole lot of money on test equipment.  If you build from kits, the test equipment requirements are minimal. 

Beyond that, we should remember that there were a whole lot of microwave systems designed and built long before simulators became useful. Hand calculation and rough paper and pencil modeling can go a long way when it comes to "just making something that works."  Beyond that, this is hobby time, cut-and-try-and-recycle can be both educational and practical.

So, 20GHz?  No firsthand experience here.  But for 10GHz you can get along fine without the fancy gear.  It isn't easy. It isn't simple. But there is a lot of good stuff on the web to help and there are even a few good kits and suitable-for-home-built designs.

[tkamiya]

Hum....  more people tell me I can't, I want to try if I can....  Hum....

Luckily, I have access to any RF equipment as my heart desire.  Not at my house but at a local lab.  I'm thinking if someone can do it on PCB, I should be able to do it without.  Not economically feasible on commercial basis but for one off?

Hum....

[tkamiya]

I've looked through LY3LP's website.  I didn't see too many off the wall creations; although, some of it may not be working the way he is describing.  As an amateur radio operator with limited fund/expertise, he is so far ahead of almost everyone else.  I admire his creativity and "making it work."

I'm thinking more along the line of going back to 50s and 60s where micro strip line was replaced by cavity and resonators.  Instead of micro stripling which is, in a way, to simulate coax, use actual coax.  I have plenty of semi-rigid lines here.

Maybe 20GHz is ambitious for starter.  I can do 5GHz, since my RF gen is limited to 8GHz.  I also have a Chinese clone of Analog Devices RF detector board to 10GHz.  That should come in handy.  There is also 15GHz PLL board popping out as well - based on TI design. 

I don't have need for economy or reproducibility.  It should be fun.

[hagster]

You shouldnt be waiting a month for a PCB. I typically wait 7 days for cheap stuff from China.

The biggest problem is finding someone who can do a well priced RF substrate. FR4 will be terrible at 20GHz. Eurocircuits do an RF pool. It costs a lot more than the chineese FR4 though.

Ref the discussions of printing transparencies. I saw a youtube video where creator used a low cost UV masking SLA 3D (similar to Anycubic proton) printer to expose the boards. Worked really well.

[coppercone2]

hey he might be doing a peaceful protest of the Chinese government 

lay off the chinvertising a bit, he clearly does not wanna do it.. go eurocircuits!!

As for the laser, I need to look into it. I am pretty sure I used a laser printer for mine... if you don't have to deal with all the fucking feed mechanisms and shit that would be brilliant, if it could get the same resolution.

I kinda wonder how hard it would be to put the printhead on a X-Y axis rather then have it work on a tensioned bend with all those mother fucking rollers and shit. Then heat it with a scanning laser or just press a hot plate on it.

Honestly I never even figured out how the laser printer works. I should look at the mechanism. I have my doubts a machine for 3d will do a good job matching the quality of the small dimensions in a laser printer but idk.

[hagster]

Here is the link to the video. Seems to work better than the laser transfer method.

Remember that these LCD screens are 4K, so fairly detailed.

https://youtu.be/-Qeq7ZgUOuE

[TheUnnamedNewbie]

lay off the chinvertising a bit, he clearly does not wanna do it.. go eurocircuits!!

Untill you find out what Eurocircuits costs for their RF pool... Even their FR4 runs are easily into the 100 euros...



If it is for one-offs, you can always try getting some RF substrates, and etch yourself. Use either microstrip (and don't touch bottom layer apart from drilling holes for ground vias) or better yet - see if you can get away with CPW (not CB-CPW, but single-layer CPW). The problem at 20 GHz is that any soldering is going to cause reflections that are unpredictable, unless you can really do it with reflow and stencils.

[coppercone2]

if you have a really fast TDR, is tuning the solder joints by slowly wicking away little bits of solder a possible procedure for those frequency ranges?

Would something like Indium Corporation pre-formed solder slabs work?

[deBug]

You can buy this inexpensive Teflon board to cut up for your experiments.
https://www.rf-microwave.com/en/nbp/nmp/10-ghz-amplifier-24ghz-doubler/su-02/#
There are some 50 ohms sections you can solder in your coax to and put MMIC, mixers etc on.
Should be doable but the slightest wire length will of course be an inductor and cause miss-match and associated losses.
https://www.rf-microwave.com/resources/products_attachments/5a43867fe89e3.pdf

//Harry

[tkamiya]

OK, you guys go ahead and talk about PCB.  I'll go my own way.

[Mechatrommer]

I'll go my own way.

good luck. dont forget to report back in your finding so we can learn...

[hendorog]

OK, you guys go ahead and talk about PCB.  I'll go my own way.

I was going to comment a while ago but forgot. I think using semi rigid coax will work fine.
As an example I've done a simple doubler for my HP 8753 which converts 0-3GHz to 0-6GHz dead bug with very short wires and it worked fine.

Most of the external connections to the TI synth are low frequency anyway I bet it will work as long as you can solder to the pads and manage things in a tidy way so as not to introduce too much noise.

I think if you cut out a square on a bit of blank PCB and used that as a ground plane, with the chip upside down it would be doable. Some of them have LDO's built in so power may be relatively simple too.

Another idea I had was to use thin plastic squares over the upside down chip as layers so you can make '3d' links over the chip without worrying about shorting stuff.

So please just go for it.

[tkamiya]

Yup,  yup, yup, and yup!

Parts are slowly rolling in, so I'll start playing with them shortly.  I've acquired lots of MMIC amplifiers, YIG, mixers, etc, so I'll start with something.  My first goal is to arrive at crude version of a microwave RF signal generator.   

[David Hess]

Would it be possible to use dead-bug style constructions?  Say, use regular PC board un-etched.  For really close connections, use piece of wire and anything longer, I also have RG405 semi-rigid coax which I intend to solder outer conductor to foil on PC.  What frequency would this type of construction begin to fail? 

I am not sure if this is feasible, but when I was back in Japan in 70s and 80s, I used to see a pre-etched PC board striplines and mixers that can be glued onto foil side of PC board sub-strait.  I wonder if I can make and order abunch of these and make microstrip lined board on the fly?

You just answered your own question.  Pre-made striplines and pad arrangements can be glued (or soldered) onto a ground plane for operation well into the GHz range although I do not know how far this can extend.  With care dead-bug style Manhattan construction can also extend into the GHz range but is not as convenient.

[cdev]

Oh, I love this, BOOKMARKED-

Foam tape is close enough to styrofoam to likely share its dielectric constant of 1. Combined with copper tape you can make traces and this works well for antennas that have to be predictable and stable in shape. You can also make a raised trace that works well as a transmission line over a copper ground plane. The uniformity of it as a dielectric may not be perfect, but its far better than what you could accomplish with wire. (Using coax is likely far better though.) Still, foam is an inherently low loss material. And its cheap and easy to do.

The downside is soldering, you really cant ever apply heat to styrofoam, it melts immediately, and is very flammable  - so dont even think about it, you totally need to put something else there underneath wherever you have to solder. Seems non-corrugated cardboard does not melt or burst into flame and so you can use that underneath where you need to apply a dab of solder to attach things safely.

[tkamiya]

I have a little more conventional method in mind.  I have some semi-rigid coax.  Where distance is necessary, I plan to use that in place of PCB traces.  Otherwise, connections will be "built" with near zero lead length.

Today, I got sweep generator cartridge fixed and it will do up to 20GHz.  Parts are almost all here, too.

Initially, I suspected calibration issue when signal dropped as much as 10db at high-end.  Most of it was actually loss from coax adapters and coax.  Duh....  I guess it's not 2GHz....

[Gerhard_dk4xp]

I wish someone would do experiments and find a known good printer that works with transparencies. I had everything from shrinkage, it sliding through without printing anything and making a terrible noise, partially printing and sliding through to make a terrible noise, crinkling up inside, and much more. Sometimes when it finally came out I was doing a happy dance. It's one of those random things. Sometimes it works great first try but sometimes your ready to cry. I swear its like the most unpredictable tool I have. Almost nothing else I own fucks off that bad for no reason.

One thing I learned is that you should wipe down your transparency sheets with 50% alcohol 50% distilled water before putting them in the printer, and let them dry well. It seems that it prevents large patches of ground plane flaking off.  I think a layer of plasticizer leaches out of them and forms on the surface and prevents proper toner adhesion. Also clean the printer tray real good and vacuum the inside of the printer while brushing it.

I use a DIN ISO A3 color laser by Kyocera and these transparencies:

< https://www.amazon.de/gp/product/B0002S4NVM/ref=oh_aui_search_detailpage?ie=UTF8&psc=1   >

No brushing, no ethanol. The transparencies are a little bit rough, so the toner attaches better.
There is no drawback since the toner must contact the photosensitive layer of the board anyway.
Before the Kyocera I had a large OKI ISO A3 color laser that produced even better black, but
it was a royal pain, a fight for every printout.

I can easily do 6 mil design rules with the laser transparencies. If it needs to be really, really good,
I go to the printer shop in the town and have them make me a film for offset printing from .pdf
or from PostScript. That is true 2400 dpi and costs less than €10 per A4 oversize page.

I use presensitized Bungard board material. They also can coat Rogers or whatever you have
at reasonable prices I was told by a collegue.
That's a completely different story than messing around with spray-on photo resist like Positiv-20.
Printout to soldering in abt. an hour.

[tkamiya]

Since you guys thoroughly changed the topic from dead-bug to PCB, let me ask this question.

Say you are home brewing a board.  What do you do to prevent copper from tarnishing?  Use solder and tin all over?  I used to have a spray but I can't find it anymore.