Dual-Band Circularly Polarized Antenna Using Mu-Negative Transmission Lines

A dual-band circularly polarized (CP) antenna based on artificial mu-negative transmission lines (MNG-TLs) is proposed in this letter. By etching dumbbell-shaped slots on the microstrip and narrow gaps on the ground plane, the zerothand first-order resonance (ZOR and FOR) modes of the MNG-TLs can be excited. Moreover, by introducing two parallel branches at the edge of metal strips in the ground plane, the CP fields are obtained at both resonance modes. The measured results show that the proposed antenna has the -10 dB impedance bandwidths of 6.3% (from 2.31 to 2.46 GHz) and 8.1% (from 3.32 to 3.6 GHz) in lower (ZOR) and upper (FOR) bands, respectively. Meanwhile, the 3 dB axial-ratio bandwidths of 10.2% (from 2.33 to 2.58 GHz) and 7.7% (from 3.35 to 3.62 GHz) can be obtained. Also, the CP radiation can be formed in the azimuth planes of 30° <; θ <; 60° and 30° <; θ <; 40° in two bands, respectively.