Transmission Line Theory And Semi-analytic Method Of Electromagnetic Compatibility Computation

As the electric technology developing fast and the electromagnetic environment complexity increasing, electromagnetic compatibility of electric system becomes more and more important. The computation model and method of electromagnetic compatibility provide the instructive foundation for electromagnetic compatibility prediction and evaluation and attract much attention. The computation model of electromagnetic compatibility can be classified as circuit theory model, full-wave theory model and transmission line theory model. We analyse several complex electromagnetic problems by using analytic method and semi-analytic method based on transmission line theory in this paper, containing transient analysis of lossless uniform transmission line, distortionless transmission line, nonuniform transmission line with nonlinear load, transient analysis of thin wire in free space and half space, electromagnetic coupling of buried wire and shielding effectiveness of shielding cavity with aperture.The main work and innovation include:1. The two-conductor transmission line field-to-line Baum-Liu-Tesche(BLT) equation is extended to multiconductor and BLT equation for multiconductor transmission line excited by electromagnetic field is eatablished based on Taylor or Agrawal model. A semi-analytic method is used to calculate the transient responses of the lossless uniform transmission line and distortionless transmission line with nonlinear loads. In this method, the frequency domain input admittance and short-circuit current are obtained by BLT equation, then the time domain input admittance and short-circuit current analytic expression in Volterra integral equation are obtained by series expansion and analytic Fourier transform, and the Volterra integral equation can be simplified, also the integral singularity and numerical Fourier transform error can be prevented.2. A method for time domain analysis of nonuniform multiconductor transmission lines with nonlinear loads is presented. Treating the nonuniform transmission line as a uniform transmission line network, the frequency domain input admittance and short-circuit current are obtained by transmission line network BLT equation, then the time domain input admittance and short-circuit current in Volterra integral equation are obtained numerical Fourier transform. Usually just several segments are needed to obtain a satisfying result, especially for transmission line with minor nonuniformity.3. A semi-analytic method is established to resolve thin wire electric field integral equation. First an approximate solution is obtained by analytic method or transmission line, then the frequency-domain iterative solution is obtained by combining the electric field integral equation and the approximate solution. Otherwise, if the wire was located in a lossless space, the inverse Fourier transform can be performed to obtain the time-domain iterative solution. Numerical results show that this method improve the approximate solution effectively, and is easy to implement numerical computation, especially suitable for early time response analysis of thin wire.4. Transmission line network model and transmission line/Green function model are presented to evaluate the shielding effectiveness of a rectangular enclosure with apertures. Different from traditional transmission line model, which represent the incidence field as a lumped source, we treat the incidence field as a distributed source by using field-to-line coupling theory and can be used to analyse the influence of incidence angle and polarization angle. Further more, the transmission line/Green function hybrid model obtain equivalence magnetic current source by transmission line model, which can be used to calculate the field and shielding effectiveness of any point inside the cavity by the dyadic Green function.