Thanks for the discussion!
I am going to answer my own question after thinking about this some more... impedance is defined as SQRT(L'/C').

if a microstrip is infinitely separated from its groundplane, the capacitance would be zero, and it would have infinite impedance! and infinitely useless.

This came about from playing with the wire-over-ground calculator, and observing what happens when the wire is a mile above ground.

https://www.microwaves101.com/calculators/874-wire-over-ground-calculator

This just in.... we have some data on a self-biased amplifier where the current drops when it is saturated. I guess this is yet another good reason NOT to use the self-biased trick on a power amp or driver amp... as the power will be limited by the shift in quiescent point.

Jim... we will put this into the monthly email blast. Hopefully get someone's attention!
Steve

That is too hard of a question for me! Can you simulate it in HFSS? Also, if there was a way to make "air microstrip" I think we could call it TEM at last. Maybe we could use magnetic levitation to hold up the conductor.

Steve

OK, I think I get it. The reason I asked is because of an "Excel mixer" I am playing with. Here is a page on it, it is still a mess

https://www.microwaves101.com/encyclopedias/excel-s-parameter-mixer

when I "mix" and amplifier's S-parameters to another frequency using high-side LO and look at group delay it is negative. But that is not a physical thing, just a figment of a slightly bogus way to simulate a receiver, right?

Thanks

yes this is possible. You need to calibrate the equipment without the LNA, then insert it, and then measure the difference in output signal.

Be careful to NOT saturate the LNA. I recommend that the input signal be 10 dB (or more) below the input one-dB compression. Good question, and good luck!

Steve

You need to make the lines 1/4 wave long at center frequency
You should plot S11, S22, S23 and S24. The rest of the parameters will be repeats of these due to symmetry. You can make a goal of -20 dB at band center for all of them.
The widths of the lines should correspond to 71 ohms. ADS should be able to calculate the line widths and quarterwave lengths for you.
That should get you started

This seems like a homework assignment...

Steve

II downloaded the Grieg and Engelmann paper, the formula is not in it. I also grabbed a few others from the 1950s, but no luck. Grieg and Engelmann were ITT employees, and microstrip was an ITT technology. The authors of the ITT reference data might have had access to memos that we will never find... I might do a little more digging.

Found it in ITT's reference data for radio engineers, 1983, sixth edition, page 24-25.
The formula came from D.D. Grieg and H.F. Engelmann, "Microstrip - New Transmission Technique for the Kilo-Megacycle Range, proceedings for IRE, Vol. 40, Dec. 1952. There are other reference, let me know if they are needed,

I will download that paper later to check it out.

Cool stuff, I like microwave history.

Steve

I downloaded the Arditi microstrip paper from 1955, he did not show this formula. See:

https://www.microwaves101.com/encyclopedias/history-of-microstrip

I have some old books gathering mold in a box somewhere, I will find them an get an answer to this question.

Steve

Bandwidth is probably the most important question as some approaches are only good for narrow band.
Also, you should consider if the outputs need to have the same transmission phase...

Steve

Back in the day, companies would provide design notebooks, and even encourage engineers to have witnesses sign pages that revealed new designs (for consideration in patents). Some changes in patent law probably caused the death of that practice. I still like drawing with a #2 pencil on Ampad Quadrille paper. Like on this page

https://www.microwaves101.com/encyclopedias/h-tree-antenna-feed

It seems archaic that people actually write stuff down, but I still do. Sad to admit this but I write on the nearest scrap of paper, like an opened envelope... if it is important I will enter it somewhere in computerland. If it sits around long enough I will forget what I was thinking and it will be thrown away. My handwriting is so poor I often cannot make out what I was thinking!

Most engineers don't use tablets, because they need to carry around a laptop to process data.

I have no real expertise in apps, but sharepoint (word, powerpoint), google docs, helpdesk... there are many ways to document designs. Collaborative tools help speed up the design process but are open to malicious intent or accidental misuse, or VPN issues. There is an entire cottage industry that will tell you what the best process is, even though the proponents have never designed anything useful in their lives.

I would be interested in hearing from other people on this topic.

Steve

This might be milking mice, but the 2.4mm will have slightly less loss than the 1.85mm....
Steve

Thanks to you both

I think I will stay away from trying to calibrate to that interface, and somehow model the adapter and subtract it off as an S-parameter file or maybe just a linear model. I am no expert on time domain but it seems like when you gate out a reflection the improvement sometimes too good to be true... This is not for device characterization, more like an acceptance test. A good design should have plenty of room for error, right?

I think about an acceptance test at a previous employer where phase tracking was needed over wideband. The operator was trained to misalign the GPO until it met the spec, then hit the save button... yikes.

Steve

I update the that page slightly, how does this look?

https://www.microwaves101.com/encyclopedias/microstrip#types

Steve

My experience with Microwave Office is that they just throw away the imaginary part of the impedance in transmission line calculations. Sorry I am no help!

Steve

Yole seems to be the most-cited microwave researcher

http://www.yole.fr/company.aspx

Of course, you have to pay for more than just a taste of the data! Other than that, I don't have any inputs. Except that 5G frequencies are very popular these days.

Steve

Can we agree to just call it quasi TEM?

https://www.rfwireless-world.com/Terminology/difference-between-TEM-wave-and-quasi-TEM-wave.html#:~:text=Quasi%20TEM%20wave%20mode%20exist%20in%20a%20microstrip%20line.&text=Hence%20in%20microstrip%2C%20wave%20propagates,referred%20as%20quasi%20TEM%20mode.

Thanks
Steve

I agree, you need a diplexer to split the signals, then operate on them independently

https://www.microwaves101.com/encyclopedias/diplexers

Steve

Tinus

Thanks for this post! I never considered the effect of surface roughness on propagation delay, but it makes sense. This deserves a new page on Microwaves101.

https://www.microwaves101.com/encyclopedias/surface-roughness-effect-on-propagation-delay

I personally think we should also start a page on "how printed circuit boards ruined my career".

Thanks

Steve