POLARIZATION-PRESERVING EVANESCENT-MODE FILTERS

摘要

Rectangular and circular waveguide evanescent-mode filters with polarization-preserving properties are presented. The filters are formed by inserting quadruple-ridged resonators in a square or circular waveguide operated below cutoff. They are especially suited in applications requiring short and compact components. The numerical technique that facilitates eigenvalue and scattering parameter computations is verified against measurements. Basic design considerations are discussed, and structural dimensions are provided for two 9.5 GHz filters with 500 MHz bandwidth. Performances are validated by independent and commercially available electromagnetic software packages. Sensitivity issues for fabrication are addressed by a tolerance analysis. Fabrication accuracy is acceptable for operation in dual vertical and horizontal polarizations but is considerably more stringent for circularly polarized applications.