A Three-Fed Microstrip Antenna for Wideband Circular Polarization

New design of a circular microstrip antenna with three feeds for wideband circular polarization is presented. Detailed theoretical analysis proves that a circular microstrip antenna, which is excited by three central symmetrical feeds with equal amplitudes and relative 120° phase shifts, can obtain good circular polarization characteristic. A broadband 120° phase shifter is developed using the metamaterial transmission line (MM TL). It consists of a Wilkinson power divider and three phase-adjusting TLs, namely a MM TL and two microstrips. The antenna is composed of two circular patches. The primary radiating patch under the parasitic patch is excited by three feeds. The proposed antenna can provide an impedance bandwidth of 54.75% and a 3-dB axial ratio bandwidth of 47.88%. The 3-dB gain bandwidth is as large as 40%, with the peak gain 8.8 dBic. In addition, the measured and simulated symmetrical radiation patterns are in good agreement.