Substrate integrated waveguide omnidirectional filtering antenna with a controllable radiation null for 5.8 GHz WiFi application

A filtering antenna composed of a monopole and two stacked circular substrates integrated waveguide (SIW) cavity for 5.8 GHz WiFi application is proposed in this letter. Cross-coupling between the feeding probe and the second SIW cavity resonator is utilized to generate a radiation null at the frequency above the working band. By properly designing the location of the feeding probe and the size of the coupling slot between the two SIW resonators, the frequency of the radiation null can be adjusted. Experimental results of the fabricated filtering antenna show good agreement with the simulated performance. The measured filtering antenna response has a return loss greater than 10 dB with a fractional bandwidth of 16.4% centered at 5.48 GHz while there is a radiation null at 6.85 GHz. Omnidirectional patterns are achieved in horizontal plane with a maximum gain of 1.1 dBi. The proposed filtering antenna has the merits of compact size and good stopband radiation suppression.