I know for high frequencies, it’s a loss issue. It order to stay TEM for coax, you have too keep reducing the diameter, then the loss increases substantially. Using coax past 26 GHz for more than a few meters length is problematic.

Waveguide has much lower loss per unit length than the equivalent TEM coax, but now dispersion becomes the issue.

So back in school, my Microwave professor said Bell had manufactured miles of circular waveguide for use in telecom, which was obsolete overnight by fiber. There was a certain circular mode that has very low dispersion, compared to rectangular.

This looks like a good discussion of the elliptical waveguide.

http://www2.rfsworld.com/RFS_Edition4/pdfs/FLEXWELL_Elliptical_Waveguide_347-369.pdf

Thanks hagster. Our purchasing dept was able to make contact with them to get a support quote.

I have the iFilter for MWO, but I haven't done any filters in years. The advantage of the integrated packages is that they can spit out schematics, with pre-populated tolerances, into the native simulator.

Thanks for the confirmation. Guess I better make double backups of the instrument control software.

Someone replied on Twitter that the entire engineering team was bought out. I've had one of their near-field antenna scanners for several years, and last year bought the EMI scanner. They made good stuff.