A Single-Layer Dual-Circularly Polarized SIW-Cavity-Backed Patch Filtenna With Wide Axial-Ratio Bandwidth

A single-layer dual-circularly polarized cavity-backed patch filtenna with wide axial-ratio (AR) bandwidth is presented in this letter. The degenerated substrate-integrated waveguide (SIW) cavity modes TE
₁₂₀
/TE
₂₁₀
cooperating with the patch modes TM
₀₁
/TM
₁₀
are utilized to achieve a wide AR bandwidth. Simultaneously, two radiation nulls, which are inherently introduced by the SIW-cavity mode TE
₁₁₀
and mixed electromagnetic coupling between the cavity and patch, respectively, are realized at both band edges to achieve a bandpass filtering response. For demonstration, a sample was fabricated and tested. The measured results show that the proposed filtenna achieves an operating bandwidth of 12% with the center frequency of 10 GHz, a peak gain of 7.4 dBic, an in-band average gain of 6.7 dBic, and an out-of-band rejection level over -13 dB.