Compact and Low-Profile Omnidirectional Circularly Polarized Antenna With Four Coupling Arcs for UAV Applications

A compact and low-profile omnidirectional circularly polarized (CP) antenna with four coupling arcs is presented. In this structure, four outer arcs are utilized to generate horizontal polarization, and an inner disk-loaded feeding pin can produce vertical polarization. Thus, omnidirectional CP radiation is achieved by combining the radiation from the arcs and the feeding pin. Four shorting pins are employed at the end of the outer arcs, which play a great role on the miniaturization of the antenna. Furthermore, the antenna's dimensions can be reduced more by loading four inner coupling arcs inside the outer arcs. An L-band prototype of the antenna is calculated, fabricated, and measured. Its final dimensions are 0.16λ
₀
× 0.16λ
₀
× 0.03λ
₀
(λ
₀
is the free-space wavelength at operating frequency). The results show the impedance bandwidth (VSWR ≤2) of 13 MHz (1429-1442 MHz). In the operating frequency band, the axial ratios are less than 2.4 dB, and the peak gain reaches 1.01 dBic. This type of antenna can meet the requirements of the weight, dimensions, and frequency bands for special unmanned aerial vehicle communications in China.