Recently, I had the opportunity to try FEST3D (Aurorasat), a professional software used to design microwave filters and passive components based on waveguide technology. It can analyze and optimize almost every kind of topology found in this field.
I especially appreciated the very large number of examples available out of the box, because as a not-expert in microwave applications, it allowed me to see all the work made by generations of RF engineers. And there is a diversity that I had not suspected!
About the speed of calculations, the software is simply amazing! The approach is to put the components into equations and calculate the solution, unlike EM full 3D simulation programs which are very time consuming. The result is usually obtained in a few seconds, while an EM simulation software take several minutes to get the result, and up to a some hours to complete a full frequency range! Moreover, the results are very close to those obtained using full EM simulation.
Fest3D main interface, reentrant cavity filter example
So, I played with this nice piece of engineering to calculate some band-pass filter, low pass filter and duplexer for our hyper-frequency amateur bands. But, my constraints for Ham bands are not the same that the professional ones. In fact, the pros often need a high bandwidth, and the band pass filters are designed to drop any inter-modulation distortion on the adjacent band. For me, with only some kHz on voice and and less one hundred Hertz using CW, I don’t have these kinds of problems (BTW I can swim :) My constraints are more focused on the construction easiness and the rejection of even and odd harmonics.
Another impressive feature, but totally out of scope for me, is the capability to estimate the maximum permissible power. I can see that my filter can supports up to 2.8kWatts, fun for me, but for sure a precious tool for a doppler radar application or a satellite broadcast design.
I will write a new post soon about these designs but I want to present my new article on slotted antennas first. Hey, first the antenna, and after, the filtering bank :)
Interdigital filter blocking a frequency (calculated with Fest3D, ParaView for the render)
More examples here.