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Home-brew X-band WR90 wageguide calibration kit for amateur radio use

Question asked by drkirkby on Mar 16, 2013
I'm hoping to encourage others in my local amateur radio club

http://www.dhars.org.uk/

to build up a couple of transceivers for the 10.000-10.500 GHz (3 cm) amateur band, using Gunn Diode oscillators. It is cheap, relatively simple, and should be more fun than buying a commercial transverter. 

The obvious thing is we need to design antennas, and the pyramidal horn looks to be the simplist to build.

One thing that would be nice, but certainly not essential, is to get the antennas on a VNA and see what they are like. There's no way I am going to buy an Agilent X11644A waveguide calibration kit for this - even used they are going to cost more than it would warrent for the limited use I would put this to. So my only options are:

1) Don't bother testing the antennas on a VNA at all. 
2) Forget trying to do calibration in waveguide, and just use a coaxial calibration of a VNA with coaxial to waveguide adapters. 
3) Try to build a calibration kit in waveguide. 

I'm wondering how difficult building a WR90  calibration kit will be, given realistically the only things I would want are the magnitudes of S11 and S21, and so accurate phase information is not critical. 

I found an old HP X910B RF Waveguide Termination for WR90 on eBay for $25. That is supposed to have a VSWR of <= 1.015:1 (return loss 46 dB) - assuming it is OK of course!

I looked in the manual for the Agilent X11644A WR90 waveguide calibration kit and see the precision on the quarter wave shim is very high - see attached. In practice, for less demanding applications, would a larger internal radius (i.e. > 0.13 mm) on the internal corners of a have a major impact? Although someone in the radio club has access to a CNC milling machine, I somewhat doubt it is possible to cut out the slot for the waveguide with such a small bend radius on a mill. Does anyone know how one might cut out a rectangular slot for waveguide in a shim whilst keeping a small internal radius? 

I'm just interested to hear from anyone who had tried to home-brew a waveguide calibration kit and compared it to a commerical one. What is realistically achievable at 10 GHz? 

My gut feeling is that a home-brew kit would be better than either not making the measurement, or calibrating in coax and adding adapters after the reference plane, but I'd be interesting in what others think. As I say, buying a commercial waveguide cal kit, even used, is out of the question. 

Dave

Edited by: drkirkby on Mar 16, 2013 5:42 PM

Edited by: drkirkby on Mar 16, 2013 5:53 PM  

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