Planar circularly polarized antennas fed by substrate integrated waveguide with asymmetric feeding and modal perturbation

Abstract In this study, a compact circularly polarized (CP) antenna based on substrate integrated waveguide (SIW) technology is proposed and investigated. By integrating a square patch rotated at 45° with a side-fed SIW structure, circular polarization is achieved through an effective phase delay introduced by asymmetrical current paths, thus avoiding the use of conventional microstrip phase-shifting networks. Trapezoidal extensions and geometric perturbations, such as via cutbacks and patch corner chamfers, are employed to enhance impedance matching and axial ratio performance. Parametric simulations confirm that optimal coupling and polarization characteristics are obtained when the via extension is shortened and the patch geometry is finely tuned. The antenna is fabricated and tested, and measurement results show good agreement with simulations. The −10 dB impedance bandwidth is 2% (2.43-2.48 GHz), and the axial ratio bandwidth reaches 1.6% (2.44-2.46 GHz), validating successful right-hand circular polarization (RHCP) operation. Unlike prior SIW-based CP designs that often rely on multilayer stacking or extended slot arrangements, the proposed single-layer, side-fed structure achieves circular polarization with a compact footprint and simplified fabrication. These results highlight the potential of SIW-fed CP antennas as practical solutions for narrowband ISM and IoT wireless communication systems where frequency stability, integration capability, and electromagnetic compatibility are prioritized over wideband operation.