| Microstrip antenna has a lot of merits such as low volume, light weight, easyconformity with carrier, good compatibility with microwave integrated circuit, easymass production, so it is connected with broad applications in several decades.However, the major limitation of these antennas is their inherently narrow bandwidthperformance due to its resonant nature. To solve the problem, this thesis appliesseveral techniques to broad the bandwidth, such as modifying the patches, offsettingthe patches, using stacked geometry etc. The simulation tools include Zeland IE3D,which is based on Method of Moments (MoM), and Ansofl HFSS, which is based onFinite-Element Method (FEM).First, the thesis introduces some fundamental concepts of microstrip antennas,such as the types of microstrip antennas, the feeding network, the analysis methods,and the conventional techniques to broad the bandwidth etc. Then, the thesis is mainlyconcerned with the design and fabrication of several broadband microstrip patchantenna elements in X band, which are supposed to be applied for the spacebomeSAR system. These antennas employ many broadbanding techniques for bandwidthenhancement. The geometries of these antennas include: (1) an aperture-coupledstacked microstrip antenna with both patches notched and offset; (2) anaperture-coupled stacked microstrip antenna with a bowtie-shaped upper patch andaperture; (3) a proximity-coupled stacked microstrip antenna with dual bowtie-shapedpatches and a rectangular aperture in the ground; (4) a proximity-coupled stackedmicrostrip antenna with dual bowtie-shaped patches and an H-shaped aperture in theground. All these antennas are fabricated and measured, the measured results mostlyagree well with the simulated results. At last, a 4~*4 array is designed and analyzed.All of these antennas studied can achieve nearly 10% bandwidth enhancementthan those unmodified antennas, especially antenna 4. which could achieve a bandwidth of more than 50% with a total thickness of less than 4mm. |
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