Patent GB-1355030-A (GB)
Title: Antenna feed system
IPC: H01Q5/00
Filed: 1973-04-11
Abstract: 1355030 Aerials HUGHES AIRCRAFT CO 11 April 1973 [14 April 1972] 17385/73 Heading H4A An aerial feed system operative simultaneously in first, second and third increasingly higher frequency bands comprises a horn defining a common radiating aperture for signals within the second and third bands, the latter signals being multimoded by means coupled to the horn. Two arms extend outwardly in opposite directions from the periphery of the horn and, in conjunction with the horn, are resonant within the first frequency band. The arms are fed at their ends nearest the horn, which is surrounded by a cavity also resonant within the first frequency band. As described, the first, second, and third frequency bands are respectively of the orders of 1, 4 and 6 GHz. A square crosssection horn 10 provides a common aperture for the 4 and 6 GHz signals, which are fed to it via a multi-mode step section 14. A 4 GHz choke section 16 surrounds the said aperture, and a dielectric material disc 18 extends radially outwards from the lip thereof, and is supported at its outer periphery by posts 24, which are mounted on a ground plane 12. Dipole arms 20 to 23 extend outwards on the disc 18 from the centres of the sides of the horn 10, and are formed with 4 GHz choke sections. Coaxial feed lines 30 to 33 operating in the 1 GHz band extend from connectors 34 to 37 alongside the horn 10, their centre conductors being connected to respective ones of the dipole arms 20 to 23, and their outer conductors being connected to the outer periphery of the choke section 16 and to the ground plane 12. A 1 GHz resonant cavity is formed by metal bands 26, 28 around the posts 24, and by the ground plane 12. Lastly, a metal cylinder 40 terminating in a flange 42 is disposed outside the posts 24. A cover which is transparent to radiation may be supported on the flange 42. The arrangement provides two crossed dipoles operating in the first (1 GHz) frequency band each comprising two outer arms and a central portion utilizing the periphery of the higher frequency horn (Fig. 7, not shown). The two feeders of a dipole may be connected to respective ports of a 180 degree four-port hybrid to provide sum and difference outputs, for monopulse applications (Fig. 8, not shown). In another mode of operation, the crossed dipoles may be fed in phase quadrature, to provide circularly polarized radiation. It is stated that the feed patterns of the system are nearly identical for each of the three frequency bands (Figs. 3, 4, 5, not shown). A second embodiment is generally similar to the first embodiment, but the horn is surrounded with a double choke section (Fig. 9, not shown). In a third embodiment a circular cross-section horn, having a double choke section, is used (Fig. 10, not shown). In fourth and fifth embodiments, square cross-section horns are used, but are provided with re-entrant portions located, respectively, at the corners and at the centres of the sides of the square (Figs. 11, 12, not shown). The dipole arms extend outwardly from these reentrant portions, and are thus diagonally located in the fourth embodiment.