H-plane multimode waveguide transition sections with large flare angles: radial and rectangular modal analyses

Waveguide transition sections that connect standard single-propagating-mode waveguides to multimode waveguides are designed using a quasioptical approach, as well as fullwave techniques based on both radial and rectangular modal analyses. The three different approaches to the problem result in the derivation of the coupled wave equations for the wave amplitudes, which are solved numerically using an iterative method as well as the Runge-Kutta method. These numerical solutions are compared with experimental results. The advantages and disadvantages of the different approaches are discussed in detail. The quasioptical approach is found to be very suitable for transition sections with small flare angles. For transition sections with large flare angles, the fullwave solutions must be used. It is shown that the radial modal analysis is here more efficient.