Project Echo: A Horn-Reflector Antenna for Space Communication

The horn-reflector type of antenna was originated at Bell Telephone Laboratories, Holmdel, New Jersey, in the early 1940's 1 and is now in extensive use in the Bell System's transcontinental microwave relay network. 2 It is a combination of a square electromagnetic horn and a reflector that is a sector of a paraboloid of revolution, as illustrated in Fig. 1. The apex of the horn coincides with the focus of the paraboloid. Since the antenna design is based on geometrical optics and has no frequency-sensitive elements, it is extremely broadband; it is not polarization-sensitive and can be used in any linear or circular polarization. The antenna is essentially an offset paraboloidal antenna, so that very little of the energy incident on the reflector is reflected back into the feed to produce an impedance mismatch. Due to the shielding effect of the horn, the far side and back lobes are very small. These features, together with high aperture efficiency, make the hornreflector attractive for use in satellite communication systems. In particular, the low side and back lobes insure t h a t when the a n t e n n a beam is pointed to the sky very little noise power is received from the ground;* the antenna is thus a low-noise transducer which permits exploitation * A discussion of the noise properties of antennas is given in Rcf. 3. 1095