Periodic Leaky-Wave Antenna With Circular Polarization and Low-SLL Properties

A periodic leaky-wave array antenna with circular polarization and low sidelobe level (SLL) for millimeter-wave application is proposed. The unit cell of the array consists of four circular split rings located on both sides of a low-loss substrate, and a planar Goubau line is used to excite the split rings to generate radiation. The antenna can realize an impedance bandwidth larger than 67%, and the 3 dB axial-ratio bandwidth is about 8.9%. The maximum gain is about 18 dBi. To reduce the SLL, the leakage loss factor α along the radiation aperture is tapered, using beamforming technique, by controlling the aperture field distribution into a cosine function. The results show that the SLL of the proposed antenna is about 6 dB lower than that of the antenna with uniform aperture field distribution. The antenna was fabricated and measured, and the experimental results are in good agreement with those of simulation.