High Performance FDTD Method And Novel Circularly Polarized Microstrip Antenna Design

Installation of various electronic sub-systems on a single warship platform with high density is able to meet the requirements of communication,radar and navigation applications at the same time.However,the near-field mutual coupling among the sub-systems may result the serious electromagnetic environment effects(E3),which can deteriorate the performance of the whole system.On the other hand,both electronic systems and platforms are very sensitive to external strong electromagnetic interference(EMI),which may lead to system malfunction and even cause their failure.Simulating these electromagnetic compatibility problems on large and complex platforms needs the efficient and accurate numerical methods.It is well known that the finite-difference time-domain method(FDTD)has been widely used to solve these problems.The time step of the conventional FDTD method is constrained by the Courant-Friedrichs-Lewy(CFL)stability condition,which makes it not effective when simulating these electrically large and multi-scale problems.In this thesis,a hybrid one-step leapfrog alternating-direction-implicit finite-difference time-domain(Leapfrog ADI-FDTD)method integrated with the thin wire algorithm is developed for simulating the near-field mutual coupling effects among multiple wire antennas on an electrically large warship platform.The main academic contributions of this dissertation are summarized as follows:(1)The field updating equations,the Yee's grid,the numerical dispersion,the stability condition analysis,the absorbing boundary condition(especially for the convolutional perfect matched layer(CPML)),and the implementation of various sources of the conventional FDTD as well as the Leapfrog ADI-FDTD are introduced.Finally,the thin-wire algorithm of the conventional FDTD is presented.(2)A hybrid one-step leapfrog ADI-FDTD method integrated with thin wire algorithm is developed for simulating the near-field mutual coupling effects among multiple wire antennas on an electrically large warship platform.Its stability analysis,based on von Neumann method,is performed in a semi-analytical way and verified numerically.It is applied to accurately characterizing complex electromagnetic environment effects on a warship with multiple thin wire antennas,where the near-field mutual coupling effects(S-parameters),the far-field radiation patterns of the antennas,the induced voltage at the port of the antennas and the surface current distribution of the warship platform under the illumination of extern electromagnetic pulse(EMP)are captured.(3)A novel low-profile dual-band and dual circularly polarized(CP)microstrip antenna is proposed.The operation mechanism of the antenna is investigated and the effects of the key geometrical parameters on the antenna performance are studied.A lumped equivalent circuit model is developed to analyze the operation mechanism of the antenna.In order to simplify the design procedure,empirical formulae are derived based on the physical parameters of the antenna.The proposed structure has been examined by both simulation and experiment,and both results agree very well.