A Single-Layer Differentially Fed Filtenna With Controllable Radiation Nulls Using Hybrid SIW Cavity and Patches

In this letter, a single-layer differentially fed filtenna with controllable radiation nulls by utilizing a substrate substrate-integrated waveguide (SIW) cavity and two patches are presented. The filtenna features a simple geometry and consists of a SIW cavity, two square patches, and a couple of complementary split ring resonators (CSRRs). The two patches, resonating at their TM 10 modes, are both collaborating with the SIW cavity, resonating at its TE 210 mode, which empowers the antenna enhancements of both impedance bandwidth and gain values. By this arrangement, a radiation null is generated at the upper edge of the operating passband due to the establishment of the cross-coupling pathway. In order to further improve the frequency selectivity, a couple of CSRRs are etched around the feeding ports. And the second radiation null is generated to sharpen the roll-off rate. These two radiation nulls can be flexibly adjusted through tuning the geometric parameters. To verify the design, the developed differentially fed filtenna prototype is fabricated and measured. The measurement results exhibit a good agreement with the simulated ones, showing a fractional impedance bandwidth of 9% (4.66-5.1 GHz) and a maximum in-band realized gain of 7.7 dBi. The developed filtenna also shows excellent frequency selectivity owing to controllable radiation nulls, high common-mode suppression, and low cross-polarization levels.