A Comparative Study Between Direct Coupled Waveguide and Combline Cavity Filters at 30 GHz

Cavity passband filters have been used in the transmitter and receiver sites due to its high quality factor Q. One application is the TV reception, where cavity filters are used to remove mobile network signals (3G, 4G) from UHF TV signals, at frequency band 470MHz-700MHz, avoiding power saturation in front-end (LNA) amplifiers placed in the top of the buildings. In this paper, we studied cavity filters characteristics at higher frequency, that of 30 GHz. We have compared, mechanically and electrically, two different air filled cavity structures, combline and waveguide with two different bandwidths, a narrow bandwidth, 300MHz, and moderate bandwidth, 4GHz. We considered only filters with Chebyshev response and the main purpose is for radar applications.