Design Of S-Band Wideband Omnidirectional Circularly Polarized Antenna

The article concentrates on research and design of S-band low-profile single- fed omnidirectional circularly polarized(CP) printed antennas.S-band is the most used frequency band for satellite communication and wireless communication. For the sake of that omnidirectional antennas could provide larger signal coverage,omnidirectional antennas could keep vehicle devices and mobile terminals communicating with surrounding devices on different azimuthal angles real-timely. CP antennas could decrease multipath distortion and polarization mismatch losses effectively to stabilize the signal transmission. Simultaneously, for the sake of printed antenna’s low-profile, ease of conformal, ease of integration and low-cost, its application prospect is very widespread. Wideband omnidirectional CP printed antennas combine the advantages of low-profile, ease of conformal, omnidirectional and CP which could improve the dimensional utilization and reduce the developing cost of communication base-stations and mobile terminals. So far as the status, the main problem which restricts the application of wideband omnidirectional CP printed antennas is that their impedance bandwidth and AR bandwidth is too narrow. Low-profile wideband omnidirectional CP antennas will play an indispensable role in the field of future wireless communications predictably.First, fundamental theories of omnidirectional CP printed antennas are investigated in the article. Basic conceptions of CP antennas and analysis methods of microstrip antennas are elaborated and analyzed. Primary implement methods of omnidirectional CP antennas and wideband techniques of CP antennas are studied theoretically deep.The article involves 3 types of single- fed wideband omnidirectional CP printed antennas. The first type is orthogonal dual-slot wideband omnidirectional CP printed antenna. The proposed antenna has a relatively low profile and a characteristic of wideband omnidirectional CP. Its performance indicators are elaborated and analyzed and sensitive parameters are researched in theory and simulation in the article. The antenna’s operating principles of omnidirectional CP and wideband are investigated eventually. Simulation results indicate that the proposed antenna could achieve reflection coefficient <-10 d B, axial ratio <3d B and gain >1d B in horizontal plane among the range of frequency 2.19 GHz ~2.60 GHz. The second type is modified ground plane with L-shape loaded wideband omnidirectional CP printed antenna. It has a characteristic of low-profile wideband omnidirectional CP. Its sensitive structure parameters are analyzed and researched in simulation in the article. After that, the antennas’ principles of omnidirectional CP and wideband are investigated deep in simulation and theory. Simulation results indicate that the proposed antenna could achieve reflection coefficient <-10 d B and axial ratio <3d B in the plane where the pitching angle θ=200 among the range of frequency 2.18 GHz ~2.62 GHz. The third type is modified ground plane with F-shape loaded wideband omnidirectional CP printed antenna. The proposed antenna which is the improved second type is aimed to change the pitching angle of its optimal omnidirectional CP plane. The proposed and second antenna’s performance indicators are compared, and the reason why the proposed one has better omnidirectional CP radiation is theoretically explained in this article. Its prototype is fabricated and measured, then simulation and measured results are compared and analyzed finally. Simulation and measured results indicate that the proposed antenna could achieve reflection coefficient <-10 d B, axial ratio <3d B and gain >3d B in the plane where the pitching angle θ=300 among the range of frequency 2.20GHz~2.62 GHz.