Testing return loss of 24 GHz antennas and transitions

Neil Smith G4DBN

I'm just embarking on machining some coax-input feedhorns and waveguide transitions to use with these Wavelab units on 24 GHz, but I don't have anything I can use to check the return loss of the transitions or horns. I can make up a 20 dB cross-coupler in waveguide, but while I can sort-of use that with my spectrum analyser as detector, assuming my best 50 ohm load looks vaguely resistive at that frequency, I can't think how to check a coax-fed feedhorn.

Without access to a 24GHz-capable VNA and the right connectors, obviously.

It is just a question of modelling it to get close and then trimming for maximum smoke on TX and use cold sky versus moon/sun noise to verify that it is working right?      Is there some magic bit of testgear I can make or obtain to get the thing tuned spot on and remove any uncertainty?

I'm thinking of using a 2.92 mm connector with a hermetic seal feedthru and a solid silver probe, because why not. They seem to be cheaper than 3.5mm or high-end SMAs. That much Sterling silver is about 10p.

It would be SO much easier with a waveguide launch PA/LNA and w/g relay, wouldn't it...

Neil G4DBN

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