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Discontinuities in reciprocal and nonreciprocal inhomogeneous waveguides McRitchie, William Kenneth

Abstract

Four types of waveguide discontinuity are investigated: (1) the interface between reciprocal homogeneous and reciprocal inhomo-geneous waveguides; (2) the interface between reciprocal homogeneous and nonreciprocal in-homogeneous waveguides; (3) a thin metal diaphragm in a reciprocal inhomogeneous waveguide; (4) a thin metal diaphragm in a nonreciprocal inhomogeneous waveguide. Mode matching is used to obtain theoretical solutions for discontinuities of types (l)-(3); experimental results are obtained for type (3) and type (4) discontinuities. Detailed studies are made of the two types of interface discontinuity. Both E-plane and H-plane dielectric loading are investigated for the reciprocal case while the configuration used for the nonreciprocal structure is that of the twin-slab ferrite loaded waveguide. Based on these analyses, the interface and the two waveguides, homogeneous and inhomogeneous, are described by relatively simple equivalent transmission circuits. In these circuits, unique normalized equivalent transmission line characteristic admittances are defined for the inhomogeneous waveguide. These admittances are shown to be not generally proportional to the wave admittances, even when such can be defined. In the nonreciprocal case, the characteristic admittances are nearly the same in the two directions of propagation although the phase coefficients can be very different. The two types of diaphragm discontinuity are investigated experimentally at a frequency of 8.5 GHz. The experimental procedure is the same for both types and requires the measurement of reflection and transmission coefficients of unmatched sections of the inhomogeneous waveguide. Theoretical results are obtained for the reciprocal case which indicate that the error in the measurements is less than ±6%.

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