Abstract: A waveguide (100) including at least one outer surface (105, 110, 115, 120) defining a waveguide cavity (140) and at least one inner surface (130, 135) positioned within the waveguide cavity (140). The inner surface (130, 135) includes a frequency selective surface (FSS) having a plurality of FSS elements (145) coupled to at least one substrate. The substrate defines a first propagation medium such that an RF signal having a first wavelength in the first propagation medium can pass through the FSS (130, 135). The FSS (130, 135) is coupled to a second propagation medium such that in the second propagation medium the RF signal has a second wavelength which is at least twice as long as a physical distance between centers of adjacent FSS elements (145). The second wavelength can be different than the first wavelength.

Abstract: A feed structure (105) for a horn antenna (100). The feed structure can include a first waveguide (110) and a second waveguide (115) having a first portion at least partially disposed within the first waveguide. The second waveguide also can include a second portion intersecting a first wall (240) of the first waveguide. The first wall can include a first frequency selective surface (244) at an intersection (280) of the first wall and the second portion of the second waveguide. The first waveguide can be operatively coupled to a first horn section (130) and the second portion can be operatively coupled to a second horn section (135).

Abstract: An antenna (100) for microwave radiation including a first horn (135) which includes a plurality of corrugations (150). At least one of the corrugations (150) is formed of a frequency selective surface (FSS) (138). The FSS has a plurality of FSS elements (305) coupled to at least one substrate (310). The substrate (310) can define a first propagation medium such that an RF signal having a first wavelength in the first propagation medium can pass through the FSS (300). The FSS (300) is coupled to a second propagation medium such that in the second propagation medium the RF signal has a second wavelength which is at least twice as long as a physical distance between centers of adjacent FSS elements (305).