Planar Circularly Polarized Antenna With Bandpass Filtering Response Based on Dual-Mode SIW Cavity

In this study, a novel single-fed low-profile circularly polarized (CP) antenna with a bandpass filtering response is proposed. It is based on a planar substrate integrated waveguide (SIW) dual-mode (TE
₁₀₂
/TE
₂₀₁
) cavity. When the vias on the edge become sparse, the electromagnetic wave leaks out while maintaining a good dual-mode filtering response. The antenna is folded in order to reduce the aperture size to form an un-splitted radiation beam with small side lobes. Owing to a rotated dual-mode operation, the fields escaping from four sets of sparse vias are approximately of equal amplitude with a progressive phase difference of 90° in sequence. CP radiation is thus achieved when the four orthogonal half-mode radiation patches are excited by the leaking field. By adopting a single feeding with two pairs of asymmetrical shorting pins, the peak gain is improved significantly and a 3 dB axial ratio (AR) response with two minima is obtained simultaneously. Long metal walls and rectangular slots are introduced to fold the current flow and change the wave direction. Consequently, sidelobe level is significantly reduced and the antenna directivity is enhanced. To verify this novel design idea, an antenna prototype with a height of 0.036λ
₀
has been fabricated using the multilayer PCB process and measured in a near-field microwave chamber. Measured results are well consistent with the simulation, demonstrating CP radiation with a flat/high gain and good filtering performance.