FDTD modeling of nonplanar microstrip antennas and coplanar structures applicable to electrooptic modulators

The Finite Difference Time Domain (FDTD) method is limited by memory requirements and computation time when applied to large problems, complicated geometries or geometries with fine features. In this dissertation, an efficient analysis of such structures is carried out by employing several techniques in conjunction with the conventional FDTD method, which improve its computational efficiency significantly without sacrificing its accuracy.; The three-dimensional FDTD has been used to calculate the characteristic impedance and the microwave effective index of coplanar waveguide structures on Lithium Niobate (LiNbO3) single crystal substrates with a yttria-stabilized zirconia (YSZ) or SiO2 buffer layer. The results shown can be a useful source to predict the modulator characteristics. The effects of anisotropy of the LiNbO3 crystal are discussed. The comparison between the FDTD and quasi-static results shows good agreement.; Microstrip patch antennas find many practical applications in which they are mounted on curved surfaces such as those of aircraft and missiles, because of their major advantage of conformability. Radomes or superstrates are employed in practice to protect microstrip patch antennas from the environmental hazards such as rain, snow, and sand. The effects of curvature on the characteristics of a single microstrip patch antenna as well as the mutual coupling between two antennas are investigated. This investigation is performed by using the conformal FDTD method. First, the effects of deformation of antenna geometry on the antenna characteristics such as the resonant frequency, the input impedance, and the radiation pattern are discussed. Second, the effects of curvature on mutual coupling between microstrip antennas on curved surfaces are studied. The results show the strong effects of the different shaped substrates on the mutual coupling. The effects of the dielectric cover on the coupling between patches mounted on the curved surface can be expected to differ from those of planar models. Numerical results for the effects of superstrate permittivity and thickness on the mutual coupling between cylindrical-rectangular microstrip patch antennas are presented. The presented results in this dissertation are useful for the rigorous analysis of microstrip antenna arrays on conformed substrates in real-world applications.