Study On Novel Planar Broadband Circularly Polarized Antenna

Nowadays, circularly polarized(CP) antenna has been widely used in various wireless communication systems because of its unique characteristics in anti-jamming and anti-fading. With the development of modern communications, CP antenna is required to have some new properties in physical structure, including miniaturization, easy integration and fabrication. Besides, excellent electrical performance is also required, such as high gain, wide bandwidth, wide beam and wide AR angle. In this thesis, a wideband, high-gain and wide-angle CP printed antenna is presented basing on the review and conclusion of various traditional wideband CP antenna designs.The main work in this thesis is as follows:First of all, the design principle and the development of various types for CP antennas are summarized, such as microstrip antennas, crossed dipole antennas and 3D spiral antennas. Then, common bandwidth-broadening techniques for these CP antennas are concluded.Secondly, a novel broadband CP antenna with “8”-shaped planar dual loop is proposed. Studies show that the structure has wide-band, wide-angle and circularly polarized radiate characteristic. Based on this structure, an antenna prototype is proposed. The feed structure of the antenna is made of double-sided parallel-strip lines(DSPSL), which provides the balancing and impedance matching. A metallic planar reflector is placed beneath the antenna to transform bi-directional radiation into directional radiation. Measured results show that the antenna has an impedance bandwidth of 19.5% and a 3-d B AR bandwidth of 23.9%. The AR angle of the antenna reaches ?50?, and the gain in the main radiation direction reaches 8dBi. The radiation efficiency of the antenna is more than 95%.Finally, according to the “8”-shaped structure, a few new configurations are investigated, including a series-feed dual rectangular loop, a parallel-feed dual triangular loop and a series-feed coplanar dual triangular loop. Meanwhile, a coplanar dual-loop broadband CP antenna is designed. Simulated results show that the antenna has an impedance bandwidth of 16.7% and a 3-d B AR bandwidth of 23.3%.