Multimode ultrahigh-frequency source and antenna

A multimode ultrahigh-frequency source comprising:

• a main waveguide forming a cavity of rectangular cross-section bisected by an E plane and an H plane intersecting in a longitudinal axis;
• two pairs of supply guides of rectangular cross-section with broad faces parallel to said plane symmetrically disposed about said H longitudinal axis, said pairs being separated from each other by a central longitudinal zone with boundaries parallel to said H plane, said supply guides opening into said cavity at an inlet thereof lying in a transverse discontinuity plane;
• a horn adjoining an exit end of said cavity disposed in a transverse aperture plane, said horn diverging in said H plane from said aperture plane outward;
• and
• an obstruction in the form of a block centered on said longitudinal axis, said block extending over a fraction of the length of said cavity from said discontinuity plane toward said aperture plane with an E-plane cross-section symmetrically converging toward said H plane for substantially stabilizing a phase center of outgoing radiation at the intersection of said axis with said aperture plane over an extended frequency band, said phase center being a point of cophasal relationship between a fundamental mode of excitation of said supply guides and a hybrid mode generated at the junctions of said supply guides with said cavity.