Research And Design Of Broadband Circularly Polarized Reflectarray Antenna

Reflectarrays have been widely used in space exploration, radar and satellite systems due to the features of high gain, low profile, low insertion loss and low cost. However, the prominent drawback of reflectarrays is the limitation of bandwidth, so many study works have been focused on improving the bandwidth of reflectarrays since which been proposed. Up to now, there are many mature designs of dual/multi-band techniques and broadband techniques of linearly polarized (LP) reflectarrays. However, the mechanism of circularly polarized (CP) reflectarrays which is different from linearly polarized reflectarrays is more complicated in analysis, so there are few broadband techniques for improving the bandwidth of CP reflectarrays. Nevertheless, CP antennas are desired in many applications due to the advantage of high robustness against environmental interference and good polarization matching compared to LP antennas. Therefore further study of CP reflectarrays is needed.The main works and innovations of this dissertation are summarized as follows:1. Rotation angle technique is first used in fixed-size cross dipole to design the CP reflectarray, and a CP reflectarray using fixed-angle and variable-size cross dipole with the same parameters is designed as a comparison. The simulation results of the two designed reflectarrays demonstrated that the rotation cross dipole reflectarray has wider bandwidth and lower cross polarized level.2. Two broadband CP ring-stub elements are proposed. The working mechanism of the two new elements is studied, and two corresponding reflectarrays are designed. Another reflectarray using the traditional split ring element is designed as a comparison. The simulation results demonstrated the feature of broadband of the two proposed CP elements and reflectarrays.3. Substrate integrated waveguide (SIW) is used to design reflectarrays with the feature of surface wave suppression to improve the gain and aperture efficiency. Variable-size square microstrip patch elements are designed in three shapes, namely patch only element, with metal edge element and SIW cavity-back element. The three elements and corresponding reflectarrays are designed and simulated, and the simulated results demonstrated that the SIW cavity-backed structure can improve the gain and aperture efficiency of reflectarrays.