B.S.T.J. Briefs: A 30-GHz Scale Model, Pyramidal, Horn-Reflector Antenna

A 30-GHz Scale-Model, Pyramidal, Horn-Reflector Antenna By R. A. SEMPLAK (Manuscript received January 24, 1979) I. INTRODUCTION In the early 1940s, the pyramidal horn-reflector antenna was invented1 at Bell Laboratories, Holmdel, New Jersey. It is now in extensive use in the Bell System 4-, 6-, and 11-GHz, transcontinental, microwave, common-carrier, radio-relay network.2 This antenna is a combination of a square electromagnetic horn and a reflector that is a section of the paraboloid of revolution. The apex of the square horn coincides with the focus of the paraboloid. The antenna is essentially a shielded, offset, parabolic antenna, so that very little of the energy incident on the reflector is reflected back into the feed to produce an impedance mismatch. Radio interference from adjacent paths limits the number of converging routes of a common carrier microwave radio system, and in recent years, demands have been made to improve the sidelobe performance of the pyramidal horn-reflector antenna. In response, blinders (metallic extensions to the side walls of the horn) have been developed 3 which provide a degree of far sidelobe reduction, i.e., sidelobes beyond 35 degrees from the axis of the main beam. To continue the investigation for ways of reducing the sidelobe levels of this type antenna, a scale model was built. The model has a numerically-machined, precision reflector, and the scaling factor is 7.5, which means that measurements made at a frequency of 30 GHz will represent the performance of a full-size antenna measured at a frequency of 4 GHz.