A Single-Layer Wideband Differentially-Fed Filtering Antenna with Controllable Radiation Nulls

A single-layer, wideband, differentially-fed filtering antenna with controllable radiation nulls is presented. The antenna comprises a square patch, an embedded square Substrate Integrated Waveguide (SIW) cavity, two stepped impedance resonators (SSIRs), and a pair of complementary split ring resonators (CSRRs) surrounding the differential-fed ports. The extension of the impedance bandwidth is achieved by incorporating the SIW cavity within the square patch, utilizing sparse metallized posts. This is accomplished by differentially exciting the TM
10
mode of the square patch, triggered by electromagnetic energy escaping from the sparse posts, and merging it with the TE
210
mode in the SIW cavity. The SSIRs are connected to both radiating edges of the square patch, resulting in the generation of two additional in-band resonances and an upper-edge radiation null. This design significantly enhances the impedance bandwidth and frequency selectivity at higher stopbands. The CSRRs, etched into the bottom surface of the SIW cavity and surrounding the differential-fed ports, create a lower-edge radiation null, which further sharpening the roll-off rate. To validate the design methodology, a prototype of the developed single-layer filtering antenna was fabricated and tested. The measured results agree well with simulated values, demonstrating excellent performance with a large -10 dB fractional impedance bandwidth of 21.2%, a peak realized gain of 9.3 dBi, two out-of-band rejection levels exceeding 26 dB, and very high selectivity.