Abstract: A two-band multimode microwave source for an antenna of a low-elevation-tracking radar comprises a higher-frequency section nested in a lower-frequency section, the two sections having E-planes perpendicular to each other. The lower-frequency section includes two outer pairs of waveguides separated by a block which convergingly projects beyond their output ends and is bisected by the E-plane of that section. The higher-frequency section includes two inner pairs of waveguides disposed within that block and separated by an obstruction lying in the last-mentioned E-plane. The higher-frequency wave emitted by the inner waveguides is made planar by a lens disposed at n output aperture of the structure which is transparent to the lower-frequency wave.

Abstract: A multimode ultrahigh-frequency source with wide passband comprises a rectangular waveguide with a cavity terminating at an exit aperture in a horizontally flared horn, an input end of the cavity remote from the horn being joined at a transverse discontinuity plane to an upper and a lower pair of symmetrically disposed rectangular supply guides that are vertically separated from each other. An obstruction in the form of a block located between the levels of the supply guides extends from the discontinuity plane forward into the cavity and converges toward the horn in the vertical E-plane, e.g. with a trapezoidal cross-section. With the supply guides excited in the basic TE.sub.10 mode, a suitable dimensioning of the block will maintain a cophasal relationship between this basic mode and a hybrid mode EM.sub.12, originating at the discontinuity plane, in the exit aperture of the cavity over a wide frequency band.

Abstract: A mixed E-plane and H-plane multimode monopulse feed is formed by a multimode E-plane horn structure, in the aperture of which metal bars or plates are arranged parallel to the electrical field. The bars or plates form discontinuities at which an odd mode of the H.sub.30 type is generated, the feed as a whole thus becoming a multimode H-plane structure. Such a feed is very useful for the production of multimode monopulse antennas of reduced dimensions.