Design And Analysis Of Wideband Circularly Polarized Microstrip Antennas

From 1970s, the technology of microstrip antenna advanced quickly. They afford the attractive features of being low profile, light weight, low cost, easy to fabricate and conformable to mounting structures, and compatible with integrated circuit technology. So they are widely employed in radar, navigation, satellite and mobile communication systems. Circular polarization, compared to linear polarization, allows for greater flexibility in orientation angle between transmitter and receiver, better mobility and weather penetration, and reduction in multi-path reflections and other kinds of interference. Moreover, the wideband wireless communication technology has the features of large communication capacity, good secrecy and anti-interference capability. Therefore, more and more investigations are contributed to bandwidth widening of communication devices. And the important part of them is wideband antennas.This dissertation mainly focuses on the novel circular polarized microstrip antenna bandwidth widening techniques. The main contributions of the dissertation are listed as below:1. A wideband circularly polarized patch antenna fed by two L-probes is proposed. The feed network comprises a cascade of a 3dB Wilkinson power divider and a broadband 90°phase shifter. By investigating the current distributions on the circular patch, a current corner is found. It means that the current distributions on the circular patch are not in order for CP operation at the center part of the patch especially at higher frequencies. By adding a circular slot on the circular patch, the circular polarization bandwidth of the antenna is widened. Then a wideband circularly polarized patch antenna with circular slot fed by two L-probe is proposed. The aggressive space mapping (ASM) technology and software IE3D are used for optimizing the antenan's parameter.2. A wideband circularly polarized patch antenna fed by four L-probes is proposed. The feed network comprises a cascade of a transformer and two broadband 90°phase shifter and output four signals. They are orientated to have phase of 0°, 90°, 180°and 270°, and excites the radiating patch by proximity coupling. This arrangement has the advantage of preserving symmetry and canceling out probe leakage radiation and probe coupling, as a result, suppressing cross polarization and widening the impedance and axial-ratio bandwidths.3. A wideband circularly polarized slot antenna fed by four microstrip line is proposed. It is a bi-directional radiator, and the radiation patterns in both sides of the antenna are similar with contrary circular polarisation, i.e. the front-radiation is right-hand circularly polarized (RHCP) while back-radiation is left-hand circularly polarized (LHCP).4. A wideband circularly polarized Serial Rotated 2x2 circular patch antenna array is proposed. The patches are excited sequentially by a broadband feed network.The performance of wider bandwidth and higher gain is achieved.