Galvanically Isolated Waveguide? 1

[logbook]

Is anyone aware of galvanically isolated waveguide sections?

I was thinking about earth loops in the DC end of the system and how to prevent them, and it occurred to me that the field would jump a small gap in the waveguide, so it should be relatively straight forward to put an insulating shim between two guides and use plastic screws to hold them together. If the gap is small then the insertion loss should be pretty small and the galvanic isolation should prevent LF current paths messing up later detection circuitry.

 

[Higgler]

A tiny gap in a waveguide makes an antenna (slotted waveguide antenna), which picks up alot of offending signals.
If the waveguide is a perfect electric conducting box, it's pretty well sealed.

kch

 

[logbook]

Yes, that’s a good point. Of course the interference would have to above the cutoff frequency of the waveguide or it wouldn’t propagate. I am not worried about pickup at this high a frequency.

 

[biff44]

In the good old days, there were two types of flanges on waveguides. The "butt" flange was just a flat piece of metal, and in low power applications you just connected one butt flange to another with the screws, and hopefully the flanges were flat enough so that the two inside walls of the waveguides made metal-to-metal contact.

Then as people started using high power in waveguides, they noticed that the flanges were melting and arcing due to very small imperfections in the flange metal-to-metal contact. That flange to flange contact point is a very high current point. So they devised a "choke" flange. A choke flange has a deep ring embedded into its face, and the distance from the short circuit at the bottom of the ring to the inside wall of the waveguide was approximately one half wavelength. Now, there was an RF short-circuit formed in parallel with the metal-to-metal contact, and the flanges stopped melting.

So, in your case, I would have one of the flanges be a "butt" flange, and the mating flange be a "choke" flange, and seperate the two with a 1 mil thick piece of kapton, and use some high strength plastic screws to hold it together. You will probably get some RF leakage out of the flange, so don't try to pass a megawatt thru it, but it should work.