A Wideband Circularly Polarized Leaky-wave Antenna

In this paper, a novel circularly polarized (CP) leaky-wave antenna with wide bandwidth is presented. The proposed antenna has a structure based on a microstrip line loaded with X-shaped slots. To generate circularly polarized waves, the feeding position of the microstrip line is shifted from the center of the X-slot to the edge. Then the straight feed line can form the phase difference between two arms of the X-slot without a meandering line, increasing the radiation efficiency. When the phase difference is 90degrees, the two arms radiate orthogonal field within required phases, thus synthesizing circular polarization. The arms of the X-slot have no spatial phase difference which makes the radiating element have a wide CP bandwidth. The simulated results show that the proposed antenna realizes available impedance bandwidth of 45.01% (2.72GHz–4.30GHz) and CP bandwidth of 13.01% (3GHz–3.42GHz). The radiation efficiency of the leaky-wave antenna is from 82.1% to 95.4% and the gain is from 2.48dBi to 3.6dBi with bi-directional radiation in the operating bandwidth. The overall size of the proposed antenna is $0. 356 \lambda_{0}\, \times 0. 356 \lambda_{0}$, where $\lambda _{0}$ is the free-space wavelength at the center frequency of the operating bandwidth. According to the phase transmission characteristic, it is convenient to extend a backward to forward scanning array with the proposed antenna. With the wide bandwidth and high scanning rate, the array has the potential to realize large-angle frequency scanning with circular polarization. The proposed leaky-wave antenna could be a good choice for radar applications and microwave imaging.