Analysis of transmission of a signal through a complex cylindrical/coaxial cavity by transmission line methods

The transmission of time-harmonic and transient signals through a complex cylindrical cavity is investigated by methods akin to microwave circuit techniques. The cavity may consist of multiple overlapping cascaded coaxial and circular cylindrical sections whose walls are perfect electric conductors. The sections may have different axial and radial dimensions and may be filled with material having different magnetic and electric properties. The first and last sections of the cavity are coaxial regions where only TEM modes exist, which allows measurements to be performed with proper excitation and termination. The cavity sections may support both a TEM mode and additional higher order modes or may support one or the other. If two sections have a common junction and each supports only one mode, then the junction is modeled by a simple two-port network. When additional modes are present, they are modeled by addition ports at the network junction. Corresponding equivalent transmission lines are associated with each mode at a physical junction. At each junction, scattering parameters are calculated and used to model the interaction of the various modes that exist. The S-parameters at each junction are determined separately by solving a simple integral equation that accounts for the structure of the junction and adjoining sections of coaxial and/or cylindrical guide. The cavity fields are, thus, associated with equivalent currents and voltages on transmission lines. A transmission line network is developed from which the input fields, fields at the cavity termination, and junction fields can be found by microwave circuit techniques or by the BLT transmission line analysis. The results from the transmission line method are compared with results calculated from a coupled integral equation analysis which has been carefully validated experimentally and with measured values on laboratory models.