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

A new class of E-plane filters based on cross-coupled resonators or over-moded cavities is introduced. The filters exhibit pseudoelliptic transfer functions with steep attenuation slopes. The metal inserts and separating wall between waveguide sections can be fabricated using electro-deposition techniques with the accuracy required for millimeter-wave applications. The filters are mass-producible, are much shorter than traditional E-plane filters, and have less insertion loss. Based on this new type of E-plane filter, highly compact diplexer structures are designed. A comparison between prototype filters and design prediction shows excellent agreement.

Novel E-plane filters and diplexers with elliptic response for millimeter-wave applications

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

A computer-aided synthesis technique for E-plane bandpass filters with improved stopband performance is developed. An optimization procedure based on equal ripple optimization is adopted. The design of a symmetrical E-plane bandpass filter with improved stopband performance is considered; higher order mode interaction between E-plane discontinuities is included in the design. The predicted filter performance shows improved stopband performance and reduced filter dimensions compared with conventional E-plane bandpass filters. The validity of the method is confirmed by the measurement of a fabricated five resonator E-plane bandpass filter with improved stopband performance.

Optimized E-plane bandpass filters with improved stopband performance

A new class of optimized finline and metal insert filters is introduced. In these filters, the ladder-type insert is located in a waveguide section which is either wider or narrower than the embedding standard waveguide. A step junction at each end forms the transition to the standard waveguide and is included in the analysis. Both filter types provide a better suppression of spurious passbands and have significantly improved stop-band attenuation. Filters with enlarged sections are useful for design at the lower end of the waveguide band, whereas the narrower version is appropriate for bandend design.

Finline and Metal Insert Filters with Improved Passband Separation and Increased Stopband Attenuation

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.

Yi-Chi Shih

Papers

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