Frequency-Agile SIW-Based Filtenna Using Evanescent-Mode Cavity Resonators

A miniaturized second-order tunable filtenna using substrate-integrated waveguide (SIW) technology is presented in this letter. The coupled-resonator theory for bandpass filter synthesis is applied to combine high- $Q$ evanescent-mode (EVA-mode) cavity resonators with a radiating slot antenna into a second-order filtenna unit. External long-range linear actuators are deployed to achieve frequency reconfiguration. The capacitive loading of the resonator is varied by changing the critical gap size between the posttop and tuning disc of the EVA-mode cavity. Using a contactless capacitive tuning scheme, the filtenna's center frequency is varied from 2 to 2.6 GHz (26%). The manufactured filtenna prototype exhibits a realized gain ranging from 2.7 to 5.2 dB across its tuning range. In addition to maintaining a compact module, the filtenna also achieves higher out-of-band radiation suppression due to the integrated filtering capability. To the best of authors' knowledge, the proposed filtenna is the first tunable cavity-based SIW filtenna presented in the literature with complete experimental validation.