Novel Wideband Circularly Polarized Antennas

Circularly polarized antenna is widely applied in wireless communication system, along with the requirement of high speed and multifunction, wideband circularly polarized planar antenna has high research value. This paper proposed a wideband and high-gain circularly polarized printed antenna which is based on the design and analysis of wideband circularly polarized printed antenna. The author’s major works are as follows: 1. A novel type approach of circularly polarized antenna design is proposed. The circularlypolarization is achieved by off-center feed bent dipole, the length of dipole in the middle of half wavelength and one wavelength, the 90°phase difference between the feed point of dipole is required by off-center feed. The space orthogonal is achieved by bent the dipole, then two requirement of circular polarization is achieved, the approximate equipment amplitude of current on the dipole is achieved by adjusted the feed point, then the circular polarization radiation is achieved. The same of two off-center feed bent dipole placed symmetry, it show the new approach can achieve circular polarization radiation; the co-polarization is 15-d B than cross polarization. 2. A novel wideband circularly polarized antenna is presented. The design approach which is off-center feed bent dipole is proposed at chapter three. The circularly polarized antenna consists of two off-center-fed bent dipole, the bent dipole is fed by coplanar microstrip line. The shorter side of each off-center-fed dipole is divided into two branches to enhance the bandwidth of the circularly polarized antenna. Experimental results indicate that the antenna achieve circular polarization with bigger wideband, an impedance bandwidth of 60% for return loss >15d B,an axial ratio(AR) bandwidth of 55% for AR<3d B, a gain of 8.5d Bi on average, and good directed radiation, which satisfy the requirement of base station antenna. 3. A wideband circularly polarized airborne base station antenna array is proposed, the base station with 2*2 antenna array consists four same wideband circularly polarized antenna. Experimental results indicate that the antenna achieve circular polarization with bigger wideband, an impedance bandwidth of 47% for return loss >15d B,an axial ratio(AR) bandwidth of 60% for AR<3d B, a gain of 15 d Bi on average. The base station cover mobile communication frequency(1.7-2.7GHz), within the operation bandwidth there is no grating lobes appear. When the antenna with 43 d Bm transmitted power placed on the aircraft with 1000 m can cover 1Km of radius.