Abstract: A dual-mode feed horn for microwave antennas includes a multi-step microwave transformer having a series of abrupt steps with progressively increasing radial dimensions. At least certain of the steps have dimensions sufficiently large to convert TE.sub.11 mode energy passing therethrough to TM.sub.11 mode energy. The transformer is preferably a binomial transformer, and the axial length of the transformer is preferably about equal to the number of steps therein multiplied by 1/4 of the average wavelength of the microwave energy to be passed therethrough. A pair of waveguides are connected to opposite ends of the transformer for transmitting microwaves through the transformer, and the waveguide connected to the larger-diameter end of the transformer has an inside diameter at least as large as the maximum inside diameter of the transformer and a length sufficient to produce a predetermined phase relationship between the TE.sub.11 mode energy and the TM.sub.11 mode energy.

Abstract: A dielectric lens for a flared microwave horn, the lens correcting the phase error introduced in microwaves passing through the horn. The lens comprises a plurality of parallel dielectric discs disposed concentrically with the horn in the path of microwaves passing through the horn. The disc have different diameters so that different portions of the microwaves pass through different numbers of the discs to compensate for the phase error introduced by the flared horn. The impedance discontinuities of the discs are matched out by appropriate spacing of the discs. The discs are preferably flat sheets of dielectric material so that they are easy to fabricate, and they are preferably supported by a central axial support means to minimize interference with microwaves passing through the discs. The number, thickness and diameters of the discs may be selected to produce substantially zero phase error in any given flared horn.

Abstract: Current-flow is suppressed on the outer surface of the horn except in a small endmost region. A reflector surrounds the horn, spaced rearwardly from the mouth. A choke used for the suppression blocks current-flow between the horn and the reflector. A high degree of uniformity of the radiation pattern over a wide forward angle is achieved.