Multi-resolution time-domain modelling technique and its applications in electromagnetic band gap enhanced antennas
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Newly emerged Electromagnetic Band Gap (EBG) structures possess multiple frequency bands that prohibit wave propagation and such stop bands are basically determined by the periodicity of the structure. Such desirable features make EBG hybrid antenna an interesting topic. Traditional full-wave techniques lack the efficiency to fully cope with the complexity of these hybrid structures, since the periodical elements are often much smaller in size than the accompanying antenna components. The Haar wavelet based Multi-Resolution Time Domain (MRTD) technique provides improved numerical resolution over the conventional Finite-Difference Time-Domain (FDTD) method, as well as simplicity in formulation. One-dimensional, two-dimensional and three-dimensional level-one codes are developed to assist the numerical modelling of the hybrid EBG antennas. An explicit form of Perfectly Matched Layer (PML) configuration is proposed, proved and presented. As a generic approach, its extensions suit every single level of Haar wavelet functions. A source expansion scheme is proposed thereafter. The concept of a multi-band multi-layer EBG hybrid antenna is presented. The theoretical prediction of antenna resonances is achieved through an effective medium model. It has been verified via numerical simulations and measurements. The 3D MRTD code is later applied to simulate such a structure. In addition, EBG enhanced circularly polarized photonic patch antennas have been studied. It is demonstrated that split-resonant rings (SRRs) and the like in EBG antennas can lead to antenna gain enhancement, backward radiation reduction and harmonic suppression. Furthermore, a circularly polarized two-by-two antenna array with spiral EBG elements is presented. The spiral element with ground via is more compact in size than the traditional mushroom structure, which is proven very efficient in blocking unwanted surface wave. Hence it reduces the mutual coupling of the array antenna significantly.
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