A computational scheme is proposed that can be applied to the analysis of cascaded waveguide discontinuities of alternating boundary-enlargement and boundary-reduction type. Based on the mode-matching technique, the proposed procedure makes use of the admittance matrix characterization of waveguide stubs. With respect to the conventional S-matrix formulation, it leads to a notable reduction of the computational effort, particularly for lossless structures. At the same time, the criterion for avoiding relative convergence problems can be satisfied. The procedure has been used to set up a very accurate and efficiency computer-aided design tool of branch guide couplers (BGCs). These are key elements of beam-forming networks for multicontoured beam satellite antennas and have to be designed with very high accuracy so as to eliminate the necessity for tuning the components realized. Design accuracies better than 0.1 dB in Ka-band are demonstrated by experimental results. >

Admittance matrix formulation of waveguide discontinuity problems: computer-aided design of branch guide directional couplers

Waveguide E-plane filters with all-metal inserts are designed by a procedure based on the reflection coefficients of axial inductive strips. The scattering matrix, representing the junction in a bifurcated waveguide, is calculated by a mode-matching method. The reflection coefficient for an inductive strip is then obtained by cascading two scattering matrices separated by a distance equal to the stripwidth. The design is valid up to moderate bandwidths, except for the narrowband design at the higher waveguide frequency range, where both the center frequency and the bandwidth are inaccurate. Possible sources of error are studied and a method minimizing the error is proposed.

Design of Waveguide E-Plane Filters with All-Metal Inserts

A method of analysis is proposed for characterizing finline discontinuities. Two conducting or magnetic planes are inserted at some distances away from the discontinuity so as to obtain a closed resonant structure. A transverse resonance technique is then used to compute the resonant frequencies and, from these, the equivalent circuit parameters of the discontinuity. In the particular case when the discontinuity is removed, the method can be used to characterize uniform finlines.

Transverse Resonance Analysis Discontinuities of Finline

The rigorous CAD of a class of rectangular and circular waveguide cavity filters which are coupled by rectangular and/or circular irises is described. The design theory is based on the full-wave mode-matching method for three key building block elements (asymmetric rectangular double-step, asymmetric rectangular-to-circular and circular-to-circular waveguide junctions) associated with the generalized S-matrix technique for composite structures. The waveguide filters may be arbitrarily composed of the key building block elements and the rectangular or circular waveguide sections between them. Finite iris thicknesses, higher-order mode interactions, and asymmetric structures are rigorously taken into account. The theory is verified by measurements. >

Field theoretical computer-aided design of rectangular and circular iris coupled rectangular or circular waveguide cavity filters

We study the effect of the relative convergence problem on the transmission matrix formulation of cascaded discontinuities. A numerically efficient modified formulation satisfying the edge condition is presented. Application is in the analysis of waveguiding structures in which a number of conductors are placed on various interfaces. Numerical results are presented for double-ridged waveguides and finlines. Applications to E-plane filters are also discussed.

An Improved Transmission Matrix Formulation of Cascaded Discontinuities and its Application to E-Plane Circuits

Convergence of modal analysis solutions of step-type waveguide discontinuity problems is studied. The convergence rate depends on the ratio between the number of modal terms retained in different regions. Guidelines for accurate and efficient computations are indicated.

K.G. Gray

Papers

Convergence of Numerical Solutions of Step-Type Waveguide Discontinuity Problems by Modal Analysis