High-Efficiency Compact Circularly Polarized Microstrip Antenna With Wide Beamwidth for Airborne Communication

The letter presents a compact circularly polarized (CP) microstrip antenna for airborne communications. The antenna adopts a square radiation patch with a cross slot to reduce the antenna dimensions and improve the impedance matching. For the high radiation efficiency of the proposed antenna, the no-resistor series feeding network is utilized to construct the antenna. In addition, the proposed structure also brings a superwide beamwidth in axial ratio (AR) radiation patterns. To confirm the performances of the novel structure, an L-band prototype of the antenna is manufactured and tested. The thickness and the side length of the antenna are 0.073λ
₀
and 0.275λ
₀
, respectively (λ
₀
is the wavelength in free space). The impedance bandwidth for VSWR ≤ 2 reaches 22.4%, and the AR bandwidth for AR ≤ 3 dB reaches 6.8%. In the overlap band, the radiation efficiency of more than 97% and the gains of more than 5.2 dBic are obtained. Especially, the beamwidth for AR ≤ 3 dB can cover more than 180°.