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Abstract

A microwave cavity filter (30, 30A) is formed of a section of waveguide (36, 114) terminated by end walls (38, 40, 44, 166, 168, 176) to form cavities (32, 34, 32A, 34A) wherein ridges (100, 102, 118, 120) are disposed longitudinally within a cavity and extend from the cavity wall partway to a central region (104, 124) of the cavity. In a preferred embodiment of the invention, the ridges are disposed symmetrically about a central plane (144), each ridge having a first component (106, 122) perpendicular to the central plane and a second component (108, 126) parallel to the central plane. A cross-sectional shape of a filter cavity may approximate a semicircle wherein one wall section (88, 130) of the filter cavity is disposed within a diametric plane (216) of the cavity. The end walls of the cavities may be constructed as iris plates with apertures (82, 182, 184, 186, 190) for coupling energy of selected modes of electromagnetic resonance within the respective cavities. Each cavity supports two orthogonal modes wherein, within the region, between the parallel second components of the two ridges, the electromagnetic fields of a first mode are parallel to the central plane and the electromagnetic fields of the second mode are perpendicular to the central plane. Mode coupling screws (80, 156) may be provided for coupling of energy between the modes within a cavity. The ridging of the waveguide sections of the cavity reduces the low frequency cut-off, thereby enabling the cavities to be constructed with smaller dimensions to facilitate their emplacement within satellite communication systems.

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