Albert E. Williams

Narrow-Bandpass Waveguide Filters

A procedure is described whereby narrow-bandpass waveguide filters having ripple in both the passbands and stopbands can be synthesized in the form of coupled waveguide cavities. Orthogonal modes in square or circular waveguides are employed to enable negative coupling elements to be realized. As a consequence, very compact filters can be constructed. Experimental results on an 8-cavity orthogonal-mode narrow-bandpass filter are shown to agree well with theory.

Narrow-band multiple-coupled cavity synthesis

A synthesis procedure of identical narrow-band high-Q cavities is presented. The procedure handles multiple couplings in a noncascaded form by synthesizing coupling impedances in one step. Necessary and sufficient conditions for realizability of singly and doubly terminated networks are obtained. An example of a sixth-order elliptic function waveguide filter is included.

A Four-Cavity Elliptic Waveguide Filter

Realization of the bandpass fourth-order antimetric elliptic filter function in a waveguide structure is described. A mathematical model is shown to accurately predict the performance of the experimental narrow-bandpass waveguide filter.

Generalized dual-plane multicoupled line filters

The authors describe the general realization of elliptic function narrow-bandpass filters constructed from two adjacent planes of microstrip quasi-TEM line resonators. This dual-plane configuration allows nonadjacent coupling to be realized through small slots between the planes. Alternate sign coupling is realized by the appropriate positioning of the slot along the resonator length. A model developed from H. Bethes small-hole coupling theory (1944) is used to predict these couplings. Adjacent resonator couplings are modeled using a coupled-line analysis modified to characterize the coupling of an inhomogeneous medium. The filter synthesis technique previously developed for waveguide cavity filters can be directly applied in designing a dual-plane filter. >

Quadruple-Mode Filters

The basic unit of the quadruple-mode filter is a cylindrical cavity designed at the degeneracy of the dual TE/sub lmn/ and the dual TM/lpq/ modes. The design and performance of a single-cavity, 4-pole elliptic function bandpass filter, centered at 4 GHz, and a two-cavity, 8-pole quasi-elliptic bandpass filter at 12 GHz are described. Both units exhibit excellent correlation between theory and experiment.