A new type of low terahertz (THz) leaky-wave antennas (LWAs) with circular polarization (CP) characteristic is proposed in this paper. The CP LWA is based on the asymmetric structure and the accidental degeneracy of modes at the gamma-point in 1D photonic crystals. Because the composite right/left handed and CP properties can be achieved by unit cells of the proposed antenna, as well as the refractive index is zero at the broadside frequency, the beam scanning of the proposed CP LWA is from backward direction to forward direction through the broadside. There won't be any deterioration of broadside performances, especially the gain whose fluctuation is only 0.25 dBi at and around broadside frequency. The gain varies from 14.85 to 16.75 dBi and the scan range is from - 23.5 degrees to 40.4 degrees over the entire operating frequency band. By optimizing the "mouth" slots, the axial ratio (AR) is less than 3 dB from 1.387 to 1.639 THz.
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