Low-Profile Diplexing Filter/Antenna Based on Common Radiating Cavity With Quasi-Elliptic Response

A low-profile single-layer substrate integrated waveguide (SIW) diplexing filtering antenna with two-pole response in each channel is presented. Synthesis technique is proposed, which allows independent design of the filtering networks for the two channels. A common slot loaded SIW cavity is used to obtain the desired radiation in both channels. The diplexing filtering antenna provides quasi-elliptic response in both channels due to source-load coupling. The filtering antenna provides a maximum broadside gain of 2.65 and 2.7 dBi at operating frequencies of 5.25 (lower channel) and 5.8 GHz (upper channel), respectively. The interchannel isolation is more than 29 dB with a channel frequency ratio as low as 1.1.