Phase Progression in Conical Waveguides

For most applications to microwave communication systems, waveguides are designed in such a way that only the dominant mode can propagate. This has been the case principally for practical reasons, as evidenced for example by problems encountered in the development of millimeter-wave systems using the higher-order TE 0 ° mode. 1 Since the waveguide in this case must be oversized, small geometrical asymmetries due to errors in fabrication, bends, and other structural perturbations cause coupling to unwanted modes, which can result in a significant degradation in performance. On the other hand, there has been considerable interest during the past several years in techniques which require the controlled excitation of higher-order modes combined with the dominant mode in, for example, a conical waveguide. Two such applications have been the TEj* -- TMq* precision autotrack system for the Telstar® satellite, 2 and the T E ^ -- T M ,, dual mode conical horn 3 which has been suggested as a primary feed configuration for low-noise satellite communication antennas. * T h e notation T E n or T M n will be used to designate conical waveguide modes. 2453