Analysis of Nonlinear Cylindrical Waveguide Taper Using Modal Matching Technique

Nonlinear tapered waveguide sections are often needed in the microwave/millimeter-wave system to connect the two waveguides of different radii. The presence of such a taper inevitably introduces unwanted parasitic modes and reflections. The modal matching technique is a powerful computer friendly method for analyzing horn antennas or nonlinear waveguides in which the actual profile is replaced by a series of uniform waveguide sections. The waveguides can have any cross section and can be propagating either cylindrical or spherical modes. The mode matching technique involves matching of the total modal field at each junction between uniform sections so that conservation of power is maintained. From this process, the amplitudes of the separate modes at the output of a junction have been deduced in terms of the amplitudes of the mode spectrum at the input to the junction. Each junction along the length has its own scattering matrix. The matrices for all junctions have been be cascaded and an overall scattering matrix has been formed. The overall scattering matrix contains the input reflection coefficient and the output transmission coefficient.