A tunable quarter-mode substrate integrated waveguide antenna

A varactor-tuned quarter-mode substrate integrated waveguide (QMSIW) antenna is presented for the first time. Quarter mode cylindrical substrate integrated waveguide cavity resonators are used to design an ultra-compact antenna with an operating frequency of ~2.7 GHz. In order to make reactive loading of the structure possible, a corner via is connected to two surface ring gaps. Frequency tuning is achieved by loading these surface ring gaps with four back-to-back varactor diodes. Using this technique, a frequency tuning ratio of ~1.7:1 (1.55-2.55 GHz) is achieved. The antenna shows similar radiation pattern with high co- to cross-polarization and front-to-back ratio for all operating states.