Abstract: A single aperture antenna system disposed to operate simultaneously in active radar and passive broadband modes is disclosed herein. The dual mode antenna apparatus 40 of the present invention includes a waveguide antenna array 50 which generates a first radiation pattern of a first polarization within an antenna aperture A described thereby. The antenna apparatus 40 of the present invention further includes a broadband antenna array 60 coupled to the waveguide antenna array 50 for generating a second radiation pattern of a second polarization within the aperture A.

Abstract: A method for designing low loss cylindrical TE.sub.011 mode resonators which permits selective placement of a transmission null at a frequency near the TE.sub.011 resonance frequency. The frequencies of the TE.sub.211 and TE.sub.311 modes, that are naturally excited in the resonator, are controlled by the angular displacement of the resonator input port and output port and by the relative amplitude of the TE.sub.011 mode compared to the TE.sub.211 and TE.sub.311 modes. Proper placement of the transmission nulls improves the selectivity of the TE.sub.011 resonator, and/or can be used to filter out unwanted noise at the frequency of the transmission null. A lumped constant analog circuit model is presented to assist in design of the resonator.