GB1081518A - Antenna system - Google Patents

Abstract

1,081,518. Aerials. HUGHES AIRCRAFT CO. Oct. 12, 1965 [Nov. 2, 1964], No. 43316/65. Heading H4A. [Also in Division H1] In an aerial system, the radiating elements of a linear array are connected by feeders of equal lengths to pick-up probes spaced evenly around the periphery of a radial transmission line to which is coupled a mode excitation device so that the fundamental and at least one higher mode may be set up, causing signals in the probes which result in beams from the array each directed at an angle which is dependent upon the order of the generating mode. As described, a radial transmission line 10, Fig. 1, comprises two spaced-apart circular plates (22), (24), Fig. 2 (not shown), which are fed by a circular waveguide (18), a coupling cavity (30) being provided. Around the periphery are disposed equally spaced probe assemblies 12, comprising pick-up probes 13 which are connected by cables 14 of equal lengths to the equally spaced radiating elements 15 of a linear array 16, said elements being mounted in a trough (17), Fig. 4 (not shown), and separated from each other by partitions (19). Successive pick-up probes (13) are connected to successive elements (15), for example, adjacent probes to adjacent elements (Fig. 11, not shown) or alternate probes to adjacent elements (Fig. 12, not shown). The upper end of the circular waveguide 18 is connected to a feed mechanism 20 comprising a mode excitation device 21 which has waveguide arms 34, 35, 36, 37 and a tuning extension (31), Fig. 2 (not shown), containing an adjustable plug (32). The waveguide arms 34, 35 and 36, 37 are connected, respectively, to the outputs of magic tees 38 and 41, whose sum inputs are connected to the outputs of a magic tee 44, and whose difference inputs are connected to the outputs of a magic tee (47), Fig. 3 (not shown). When a signal is applied to the sum input (45) of the magic tee (44), outputs in phase are delivered to the waveguide arms (34), (35), (36), (37) and the TM 01 mode is excited in the circular waveguide (18), causing the fundamental TEM mode to be generated in the radial transmission line (10). The pick-up probes 13 are excited in phase and a beam (60), Fig. 13 (not shown), is developed normal to the linear array 16. If a signal is applied to the difference input (46), Fig. 3 (not shown), of the magic tee (44), the outputs to the waveguide arms (34), (35) and (36), (37), respectively, are in anti-phase and a TE 11 mode is excited in the circular waveguide (18). Similarly, when a signal is applied to the difference input (49) of the magic tee (47), a TE 11 mode is excited in the circular waveguide (18), but it is orthogonal to that excited by a signal applied to input (46) of the magic tee (44). The two TE 11 modes develop higher order circumferential modes (m = Π1) in the radial transmission line (10), which correspond to beams (61), (62), Fig. 13 (not shown), angularly displaced on each side of the broadside beam (60). The same considerations apply for reception. In another embodiment, Fig. 5 (not shown), the radial transmission line (10), is fed by a coaxial line (76) from a mode excitation section (75), Fig. 6 (not shown), comprising two rectangular waveguide arms (80), (82) leading into a coaxial segment (77) by suitable transition sections. The segment (77) is connected to the coaxial line (76) and the arms (80), (82) are connected to the outputs (73), (74) of an E- plane folded magic tee (70). When a signal is applied to the sum input (72) of the magic tee (70), outputs in phase appear in the arms (80), (82) of the mode excitation section (75) and a TE 11 mode is developed in the line (76) (Fig. 8, not shown). When a signal is applied to the difference input (71), however, outputs in antiphase appear in the arms (80), (82) and the TEM mode is developed in the line (76). An orthogonal TE 11 mode may be fed to the radial transmission line from the other side thereof. In a further embodiment, the excitation system for the radial transmission line (10) comprises a coaxial line (100), Fig. 10 (not shown), feeding from the top, and a circular waveguide (102) feeding from the bottom. The TEM mode and a TE 11 mode are developed in the line (100) and an orthogonal TE 11 mode in the waveguide (102). Axial septa (103); (104) within the feeders (100), (102) are at right angles to each other and prevent the escape of either TE 11 mode into the feeder for the orthogonal mode. In a further embodiment, a transmitter (90), Fig. 9 (not shown), is connected to the first port of a circulator (91) and a coaxial line feeder (92) for the radial transmission line (10) is connected to the second port thereof. The TEM mode is excited in the line (92), which sets up equi-phase signals in the elements of the linear array, resulting in the transmission of a broadside beam. During reception, however, as well as the TEM mode in the coaxial line (92), orthogonal TE 11 modes are developed in an oppositely disposed circular waveguide (95) and are separated from each other in an orthogonal mode transducer (96). The " inphase " signal corresponding to the TEM mode is passed from the second to the third port of the circular (91), and thence by a line (93) to one input of a 1: 2 power divider (94). A signal having a phase relation which can be designated as cos # is obtained from one output of the mode transducer (96) and is applied to the other input of the 1: 2 power divider (94), the output of which is then equivalent to a (1 + cos #) = 2# 2 cos - aerial aperture distribution. 2