| The research of patch antennas based on photonic-bandgap(PBG) structures is a relatively new area. The goal is to improve the performance of the patch antennas by using the special features of PBG structures. Though some good research results have been obtained by scientists in the world, there still exit some problems to be solved for improving the performaces and reducing the size, weight and cost. The following research work has been done for these problems in this thesis:Patch antennas with PBG substrates have been studied thoroughly. A patch antenna with air holes in the substrate has been designed. The finite-difference time-domain(FDTD) method together with the perfectly matched layer(PML) boundary treatment has been used to study the performance of the antenna. It is shown that the surface waves are significiently suppressed, the frequency bandwidth is improved, the sidelobe levels are reduced and consequently the gain in the forward direction is improved by 14 dB (about 4 dB higher than the value reported previously). A patch antenna with etched holes on the ground plane is also studied. The performance of the antenna at the resonant frequency is analyzed by using the FDTD method together with the PML boundary treatment. The results show that the surface waves are suppressed greatly, the bandwidth is improved and a 1 OdB reduction on the sidelobe level is achieved at the 110° and 260° directions in the E plane.A new PBG cover formed by digging air holes in the material is studied.lt is easier to be fabricated compared with the structure reported before. The cross-sectional size of the PBG cover is greatly reduced and its dimension is only 145 mm x 145 mm(which is about 2/3 smaller than the cover designed by Thevenot et al., and 6/7 smaller than the one designed by Qiu et al.). The performance of the PBG antenna using the new PBG cover together with a PBG substrate is studied by the FDTD method together with the PML boundary treatment. The numerical results show that a more focused beam radiated in the broadside direction is achieved.The gain of the PBG patch antenna in the forward direction is improved by about 6 dB. The radiation directivity is improved significantly and reaches 11.5 dB, which is0.4 dB less than the maximum value that is allowed physically for this size of the antenna (This difference is about 4.1 dB less than the difference achieved by Thevenot et al., and 1.5 dB less than the one achieved by Qiu et al.). Good experimental results have been obtained and agree well with the simulation results.A new patch antenna with patch rings is studied. A patch antenna with a corrugated soft surface ground plane is studied firstly for comparison. The FDTD method together with the PML boundary treatment is used to calculate the input return loss and the radiation pattern. The simulation results show that the bandwidth is improved, the radiation pattern becomes more rotationally symmetric and the sidelobe levels are greatly reduced. The experimental results agree well with the theoretical predictions. To overcome the drawbacks in the weight and cost of the antenna with the corrugated soft surface, a new patch antenna with patch rings is designed. Its weight is about 1/4 less than the antenna with the corrugated soft surface and it is inexpensive. Good experimental results are obtained. The radiation pattern of the antenna is more rotationally symmetric, and a more reduction on the sidelobe levels of the antenna is achieved as compared to the antenna with the corrugated soft surface.In conclusion, in the present thesis both theoretical and experimental research works have been carried out intensively on patch antennas based on photonic-bandgap structures. It is shown that our photonic bandgap structures can greatly improve the performance of the patch antennas. These patch antennas with photonic bandgap structures are more superior than conventional patch antennas, and have potential applications in many areas such as mobile communications, satellite and aircraft communications.
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