A Dual-Band Omnidirectional Circular Polarized Antenna Using Composite Right/Left-Handed Transmission Line With Rectangular Slits for Unmanned Aerial Vehicle Applications

A dual-band omnidirectional circularly polarized (CP) antenna using composite right/left-handed (CRLH) transmission line (TL) with miniaturized size is presented. The antenna consists of a circular radiation patch and a circular ground connected by three copper shorting vias, on which three rectangular slits are etched. Two sets of opposite branches are arranged in sequence around the radiation patch and ground to widen the impedance bandwidth (BW). The zeroth-order resonance (ZOR) structure by CRLH-TL and meandering technology allow miniaturization of the antenna, and rectangular slits realize wide low axial-ratio (AR) performance in the azimuth plane. The dual-band antenna is fabricated and measured. The overall size of the antenna prototype is only 0.208λ
_L
× 0.208λ
_L
× 0.026λ
_L
, where λ
_L
is the free-space wavelength at the center working frequency of the low band. The BW in the lower band has a range of 2.39 GHz to 2.42 GHz, equivalent to 1.25%, and that of the upper band has a range of 5.6 GHz to 6.0 GHz, equivalent to 6.90%. The AR bandwidth (ARBW) has ranges of 1.9 GHz to 2.6 GHz at 2.4 GHz, approximately 29.2%, and 4.6 GHz to 7.3 GHz at 5.8 GHz, equivalent to 46.6%. The overlap BW covers the two frequencies of unmanned aerial vehicle (UAV) image transmission, 2.4 GHz and 5.8 GHz in China.