Abstract: A coupler for extracting energy in the TE.sub.21 mode from a circular waveguide propagating energy in both the TE.sub.11 and TE.sub.21 modes, characterized in that an annular iris on the inner circumference of the waveguide and a longitudinally stepped transition portion of the waveguide define therebetween a TE.sub.21 mode resonant cavity which is coupled via a narrow axially extending rectangular slot contained in the wall portion of the waveguide which defines the cavity. At least one external resonant chamber may be provided on the waveguide through which the TE.sub.21 mode energy is extracted and transmitted to a detector thereof via the slot, which chamber cooperates with the resonant cavity to define a multiple resonant filter for improving the matching to the TE.sub.21 mode while reducing the perturbation to the TE.sub.11 mode.

Abstract: A dual mode directionally coupled band reject filter apparatus having coaxially aligned first and second cylindrical cavity members which are asymmetrically mounted to the broadwall of a waveguide. Both cylindrical cavity members include a plurality of tuning screws to establish elliptic-type responses.

Abstract: Waveguide lenses characterized by wide bandwidth, polarization-insensitivity, and absence of physical zoning steps. A waveguide lens constructed in accordance with the variable cut-off frequency approach of the invention comprises a two-dimensional array of individual waveguide elements arranged in proximate juxtaposition extending between inner and outer lens surface contours. At least a portion of the outer surface contour follows a constant group delay surface contour, and the individual waveguide elements are configured so as to have cut-off frequencies individually selected so as to compensate the phase lengths of individual waveguide elements to provide constant phase delay. For determining the various cut-off frequencies and thus phase lengths, the individual waveguide elements may have various cross-sectional configurations, various fillings of dielectric material, or both.

Abstract: An equalizer cavity apparatus which is directionally coupled to a rectangular waveguide utilizes a circular waveguide with an adjustable RF absorber therein to lower the quality factor, Q, of the equalizer cavity.