Circularly Polarized Leaky Wave Array With Wide Axial Ratio Beamwidth and Low Sidelobe

In this communication, a circularly polarized (CP) leaky wave antenna (LWA) array with a wide 3 dB axial ratio (AR) beamwidth and low sidelobe level (SLL) is presented. To overcome the shortage of narrow 3 dB AR beamwidth of conventional substrate integrated waveguide (SIW) slot element, an improved CP LWA element is introduced by placing a square patch above the perpendicular slots. The composite radiation mode of the new element has a stable spatial phase difference between the orthogonal polarizations within a wide range of angles, which ensures the wide 3 dB AR beamwidth and the theoretical analysis validates it. Furthermore, by adjusting the size of the proposed LWA element, it is feasible to control the leakage constant while maintaining good CP radiation, which is beneficial for low SLL pattern synthesis. By using Taylor pattern synthesis, a ten-element CP linear array prototype is designed, fabricated, and measured. At the center frequency of 14.2 GHz, the wide 3 dB AR beamwidth of 113° and low SLL of −20.9 dB are realized. Within the measured effective operation band of 13.9–14.6 GHz, the peak gain is 16.1 dBi with gain variation less than 0.6 dB.