On The Novel Technology For Circularly Polarized Antenna

With the rapid development of antenna technology, circularly polarized (CP)antenna is widely applied in radio frequency identification (RFID) system and satellitenavigation receiver and other communication systems with the advantages ofanti-multipath interference. Four types of CP antennas are investigated and excellentperformance has been obtained with the novel technology for modern circularpolarization in this dissertation.Based on twin-diamond-shaped overlapping patch, wideband CP antenna ispresented by improving the conventional double-fed structure. Two degenerated modes(TM01andTM10modes) with equal amplitude and90degrees phase difference aregenerated and good circular polarization is acquired by a coupling feed and a simplequarter-wavelength (0.2850) transmission line. In addition, the radiating patch andthe driving patches are printed on the same side of the substrate, and widebandperformance is obtained by gap-coupled feed. The experimental results show that therelative bandwidths of10-dB return loss (RL) and3-dB axial ratio (AR) for the antennaprototype are about20%(2.15-2.62GHz) and9.2%(2.31-2.53GHz), respectively. Themeasured maximum gain in broad-sight direction is8.2dBi and the antenna is acandidate for2.4GHz RFID reader antenna.Two types of planar CP antennas are presented with bidirectional radiation. Adual-frequency and dual-sense CP antenna fed by microstrip line which utilizes twoannular slots is proposed. Right handed circularly polarized (RHCP) and left handedcircularly polarized (LHCP) radiation can be acquired at lower frequency1.6GHz andhigher frequency2.4GHz by introducing asymmetrically truncated corners and notches.Another asymmetric annular patch is used to excite two orthogonal modes to generateRHCP wave around2.45GHz for the coplanar waveguide (CPW)-fed planar antenna.These two antennas have been fabricated using low-cost printed circuit board (PCB).The measured results have a good agreement with the simulated results, whichdemonstrates the proposed antennas suitable for the practical applications.A high gain CP antenna array comprised of five antenna elements is designed tomeet practical application requirements. The CP radiation of the antenna unit isobtained by the patch with truncated corners. The CP bandwidth is broadened usingcapacitive coupled feed structure and the designed array has good performance. The center frequency of the array is at1561MHz and its overall dimensions are1.8201.8200.120. The gain of the array is more than15.3dBi over the entirefrequency range.