A Single-Layer Wideband Differential-Fed Filtering Antenna With High Selectivity

In this communication, a single-layer, wideband, differential-fed filtering antenna with high selectivity is proposed. The developed filtering antenna possesses a simple structure and consists of a square patch, a square substrate integrated waveguide (SIW) cavity, a pair of symbiotic stepped impedance resonators (SSIRs), and a pair of complementary split ring resonators (CSRRs). The SIW cavity formed with sparse metalized posts is embedded in the square patch, and the impedance bandwidth can be broadened by merging the TM10 mode of the square patch, excited by the electromagnetic energy escaping from the sparse posts, with the TE210 mode in the SIW cavity through differential excitation. The SSIRs are connected with both radiating edges of the square patch. And two extra in-band resonances together with an upper-edge radiation null are simultaneously generated, so the impedance bandwidth and the frequency selectivity at the higher stopband can be significantly improved. The CSRRs, surrounding the differential excitation ports, are etched into the bottom surface of the SIW cavity, and a lower-edge radiation null is produced to further sharpen the roll-off rate. By adjusting the geometrical parameters of the SSIRs and CSRRs, the positions of the two radiation nulls can be independently controlled. For verifying the design method, a prototype of the developed single-layer filtering antenna has been fabricated and tested. The measurement results are well consistent with the simulated values, indicating good 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 of more than 26 dB, and very high selectivity.