Theoretical Proof and Implementation of Balance Conditions for Simultaneous Open Stop Band Suppression and Circular Polarization in Slot-Loaded Waveguide Leaky-Wave Antennas

Abstract This manuscript presents a comprehensive theoretical and experimental study on rectangular waveguide (RW)-based leaky-wave antennas (LWAs) with longitudinal and transverse slots. The main contributions are as follows. First, it is theoretically demonstrated that the longitudinal slot operates in the shunt mode, while the transverse slot corresponds to the series mode. Second, it is proven that for the TE₁₀ mode, achieving a shunt radiation mode requires an asymmetric structure with respect to the longitudinal axis. Third, it is shown that a 90° phase difference exists between the series and shunt components; thus, by properly adjusting the longitudinal asymmetry, circular polarization (CP) can be realized. Fourth, balance conditions are derived to simultaneously suppress the open stop band (OSB) and achieve CP radiation. Finally, based on the proposed theory, two periodic slot-loaded LWAs are designed, and one prototype is fabricated. The simulated and measured results validate the theoretical findings, demonstrating the effectiveness of the proposed approach.