Circling back to the original intent of this thread, I was looking for a way to tune a cheap thick-film resistor, grounded with an inductive via hole. Adding some tuning stubs and changing the resistor value are all fair game, or any other tricks you might have. I don't want to worry about radiated power, but I was thinking the resistor would be mounted to exposed traces (microstrip, not stripline). DC to 40 GHz with 20 dB return loss would be nice... and performance to 60 GHz would be appreciated. I'll post what I come up with at some point.

This thread is pretty old. I had seen a pile of maybe 100 bent probes going to the dumpster before I posted it. No one responded, and all those probes went out with the trash. Then a month or so ago, someone asked if they were still available. Any RF lab consumes probes over time, I went and checked out what was newly trashed. After looking at about twenty ruined probes, I can say that most of them are beyond repair. I grabbed a half dozen that might have some hope and intend to ship them shortly, to see if they can be restored. I'll post the result later. Meanwhile, every day, somewhere, an RF probe crashes.... be careful with them!

Steve

I'd post some images of it but I can't figure out how to do that here...

Wow, great minds think alike. I also built a tapered resistive open-circuit stub. You can tune it with some conductive stripes, i.e. the load is like five resistors in series. I will have to dig that up and take a photo. Of course it was on alumina, lately everything is on circuit boards.

You can buy an HP-67 on Ebay to try it out...

https://www.ebay.com/itm/286361753781

- Steve

Wow, I need to post a photo of my library as well! I gave away some of the lesser titles. I have boxes and boxes of old app notes and technical memos, I have fooled myself into thinking I will someday do something with them... Some of the old memos are comedy gold. Imagine someone writing a memo about how impressed he was with his own work, then further imagine he became a VP...

Steve

I found him (thanks, Chris!), then jumped down the another rabbit hole. Thanks to a certain patent troll, we even have a photo of Mr. Bagley.

https://www.microwaves101.com/encyclopedias/bagley-power-divider

That's a good article. Next time I get stuck measuring NF I will be better prepared. Thanks for all your help!

This could be a problem with the input match that the detector provides. Looking at a tunnel diode detector data sheet is spec'ed at 2:1 VSWR

https://www.pasternack.com/images/ProductPDF/PE80T6000.pdf

looing at a Schottky detector, the input match is not even specified

https://www.pasternack.com/images/ProductPDF/PE8004-P.pdf

I am not saying this is the smoking gun, but maybe the combined LNAs are conditionally stable. It would be worth looking at broadband input match on both detectors.

Steve

We will attempt to get another venue for next year at IMS 2025. Hopefully a livestream! This year was a bit of a broken play because it was not planned early.

If there are any full-sized microwave engineers out there, we still have a lot of XXL and XXXL Microwaves101 tee shirts. Contact us if you want one. It's like five bucks to mail a shirt in the US, we don't mind paying. But if you are out of the country, we might want you to kick in part of the postage using Venmo or whatever....

Steve

Did some experiments with putting an isolator in front of the LNA and trying to subtract out its loss. It definitely improved the bumpiness on the Y-factor measurement.

Oscillations are a possibility, when we started taking data the NF was like 10 dB but the amp was singing like crazy. Capacitors and resistors seems to have fixed that.

I will look at the VSWR uncertainty calculation...

I think part of the larger picture is that just maybe the noise figure shown in a MMIC data sheet was measured on-wafer, and the user has to suffer some loss mounting it to a circuit board. For yucks we might but a Qorvo CMP2626 LNA eval board

https://store.qorvo.com/products/detail/qpa2626eval-qorvo/597407/

But it does not appear to have a "through line" to calibrate out the board losses.

Not sure why it would be a Doherty amplifier, it looks like a simple two-stage power amp to me. Two FETs driving four FETs. Could the input and output be through the board? Maybe send a photo of the board flipped over?

That is an interesting board! I found an article where those transistors were used at L-band to make power amplifiers

https://cds.cern.ch/record/180485/files/CM-P00059135.pdf

Ignore this advice if the amplifiers are in coax packages....If you are talking about cascading MMIC chip amplifiers, 60 dB gain is enough so that a little radiation from wirebonds or microstrip can cause positive feedback and then oscillations (You need to have some space between them and preferably channelize the signal path with small enough cross-section to cut off any waveguide mode where gain is available (not a problem when you are at 2 GHz!) In a pinch some RF absorber over the top of the MMICs can do wonders, but I believe that if you put absorber over the first MMIC you might degrade the noise figure. Good luck and let us know how you solved this issue... even better if you supply some photos and text for a Microwaves101 page!

We will be "presenting" at one of the Young Professional events at IMS 2024, I think on Thursday. If anyone wants a Microwaves101/MTTS T-shirt, we will have them there. Stop by the booth any time during the week and use the password "Afghanistan Bananastan" and we might be able to hook you up with some merch if you can't make the YP event.

And there is little chance of asking something anonymously on LinkedIn. But your peers can admire the professional glamour shot that you posted of yourself to comply with your company's social media directives

https://www.linkedin.com/in/steve-huettner-12817a77/

It seems like answers to questions that are posted are routed to just the question asker, and not posted as a comment. That does not seem like the best way to build a community...

Steve

Glad to see you there! It turns out we were too late to organize a livestream. Instead they may allow us to have a booth a Women in Microwaves or Young Professionals event which of course is members only and not what we had in mind. But it looks we still have time to launch an MTT-S Microwaves101 tee-shirt to give away... We will try to get some interest in a live stream for 2025 IMS, however, the only way to get something like that launched for sure it to get more involved in IMS committees, which is not something we are anxious to do. We'll keep you posted!

Mike... that is an excellent article. At first glance I don't see any mention of the amplifiers load-pulling each other in a reactive combiner. I think that could be a significant effect.

I totally forgot about the forum (message board) being wiped clean. It never really came back after that, people moved on. Here we are, the proverbial tree falling in the forest.

Thanks for your thoughts!

Steve