Study On Electromagnetic Bandgap Structure With Bow-tie Units

The mobile communications and personal communications have been rapidly grown with wide applications in recent years. The microwave circuit with compact and high performance is one of the critical technologies in next generation wirelesse communication system. Electromagnetic bnad gap (EBG) and its applications in microwave and millimeter wave field present a new path for the communication system towards high compactness, performance and reliability. Based on the characteristics of EBG structure, the frequency chacteristics of single-layer and double-layer EBG structure with bow-tie units are discussed in this thesis respectively. And then particle swarm optimization (PSO) algorithm is used to optimize the structures.The main research works are discussed as follows:1. An EBG structure with bow-tie unit is researched in this thesis. Based on the theory of microwave 2-ports network, its frequency chacteristics is obtained. The simulaton results show that the performance of the EBG structure with bow-tie units is good when it tapers with hanning discipline. At this time, the bandwidth is about 2.87GHz at -10dB, and its relative bandwidth is 55%. The EBG structure with defect forms a passband with a certain bandwidth in the stopband, and the center frequency of passband may be adjusted easily.2. The EBG structure with bow-tie units is optimized by using PSO algorithm. As we all know, the standard PSO has some shortcomings, such as premature convergence, searching precision lowness and so forth. In order to solve the problems, considering the simulation of natural death process of 5% B-cell in biology clone selection, this thesis proposes particles updating algorithm according to the theory of chaos and principle of mutation; and then selects the updated particles in terms of simulated annealing method. The simulation results show that the EBG structure with bow-tie units has a good stopband performance and large relative bandwidth. The passband ripples of the optimized EBG structure are very small and basically symmetrical. Frequency characteristic of the optimized EBG structure is very excellent.3. A double-layer EBG structure is studied, including the bow-tie units etched on the upper layer and circles etched on the substrate. The radius of the circles and relative positions between circles and bow-tie cells are determined by simulation. For eliminating the passband ripples, the Chebyshev distribution is adopted to taper the area of the etched circles. This makes the frequency characteristics great.4. A double-layer EBG structure is studied, including the bow-tie units etched on the upper layer and cirques etched on the substrate. PSO algorithm and the HFSS software are combined to optimize the sizes of the cirques. After optimizating, the relative bandwidth at -10dB and the attenuation of stopband are, respectively, increased 22.69% and 15.26%, and the passband ripples are reduced 76.76%. The frequency characteristics are very well after optimization.