A compact circularly polarized microstrip patch filtenna based on reusable dual‐mode substrate integrated waveguide cavity

Abstract

In this letter, a compact circularly polarized (CP) microstrip patch filtenna designed by reusing dual‐mode substrate integrated waveguide (SIW) cavity is proposed. The dual‐mode SIW cavity, operating at its TE120 and TE210 modes, can be used not only as the first stage resonator of the filtering network but also feeds the four microstrip patches working at their TM10 and TM01 modes. A pair of asymmetric perturbed posts is inserted in the SIW cavity to perturb the electric field distributions of TE120 and TE210 modes so as to achieve one axial ratio (AR) minima. The other AR minima is realized by sequentially exciting the four orthogonal microstrip patches via the four rectangular slots that are etched on the top surface of the SIW cavity. In addition, four metal posts penetrated the SIW cavity is employed to improve the impedance matching. For verification, a CP filtenna prototype centered at 5.13 GHz is designed, manufactured, and tested. The measured results agree well with the simulated ones, demonstrating a fractional impedance bandwidth of 6.9% (4.95–5.3 GHz), a 3 dB AR bandwidth of 4.2% (5–5.21 GHz), and a maximum boresight realized gain of 8.4 dBic.