GB1189463A - Improvements in and relating to antenna system - Google Patents

Abstract

1,189,463. Aerials; radio direction-finders; radio signalling. HUGHES AIRCRAFT CO. 21 June, 1967 [8 July, 1966], No. 28725/67. Headings H4A, H4D and H4L. [Also in Division H1] An aerial system comprises an aerial structure which is adapted to receive signals from any bearing, a waveguide coupled to said structure and arranged to receive therefrom linearly polarized waves, a polarization converter in said waveguide, and two energy coupling means extending into said waveguide and arranged to receive the waves propagated through said converter. As decsribed, an aerial structure 10, Fig. 1, is formed by a plurality of spaced slots 16 in the upper end of a cylindrical waveguide 14, said slots being located between two flared frusto-conical reflectors 18, 20. Within the waveguide 14, and below the slots 16, is a polarization converter, consisting of two diametrically opposed quarter-wave plates 22, 24. Below the said plates are a pair of output probes 26, 28 connected to respective receivers 34, 36. With this arrangement, energy incident upon the aerial is coupled to the waveguide 14 in the TE 11 mode. The polarization converter ensures equal coupling to each output probe 26, 28 and hence equal excitation of each receiver 34, 36. If one receiver fails, the other remains excited. In a second embodiment, an aerial structure (10<SP>1</SP>), Fig. 3 (not shown), waveguide (14<SP>1</SP>), diametrically opposed quarter-wave plates (22<SP>1</SP>), (24<SP>1</SP>) and output probes (26<SP>1</SP>), (28<SP>1</SP>) are provided as shown in Fig. 1, but there is an additional polarization converter intermediate the aerial structure and the quarter-wave plates. This may consist of a ferrite sleeve (40) inside the waveguide with an energizing coil structure (42) outside. The probes (26<SP>1</SP>), (28<SP>1</SP>) are disposed at 90 degrees to each other and are displaced by 45 degrees from the quarter-wave plates (22<SP>1</SP>), (24<SP>1</SP>). By suitably energizing the coil structure (42) in one sense, the signal energy is coupled to the probe (26<SP>1</SP>) and to an associated receiver (34), and by suitably energizing the coil structure (42) in the other sense, the signal energy is coupled to the probe (28<SP>1</SP>) and an associated receiver (36). The linearly polarized wave in the waveguide due to reception of a signal by the aerial structure is converted to a right or left-handed circularly polarized wave by the additional polarization converter and then is converted by the quarter-wave plates to a linearly polarized wave aligned with one or other of the orthogonally disposed output probes. If the coil structure (42<SP>1</SP>) is not energized, there is equal coupling of energy to each probe. In a third embodiment, the output probes 26, 28, Fig. 4, of an aerial structure and waveguide coupling arrangement of the kind shown in Fig. 1 feed through R.F. amplifiers 50, 51 to orthogonally disposed input probes 54, 55 at one end of a cylindrical waveguide 56, and also to the inputs of a circuit comprising mixers 60, 61, a local oscillator 62, I.F. amplifiers and limiters 63, 64, and a phase detector 65, from which an output is obtained indicative of the bearing of an incoming signal received by the aerial structure 10. In the waveguide 56 the input probes 54. 55 are followed by quarter-wave plates 68, 69, a ferrite element 40<SP>1</SP> with associated coil structure 42<SP>1</SP>, quarter-wave plates 71, 72, and output probes 73, 74 which are connected to the inputs of receivers 34, 36. A current source 80 may be connected to the coil structure 42<SP>1</SP> by a switch 84 so that there is input either to the receiver 34 or to the receiver 36. If the coil 42<SP>1</SP> is not energized, there is input to both receivers. When the ferrite element is activated the state of polarization of waves passing from the input to the output side is converted from linear to circular, either right- or left-handed. As shown, the outputs of the receivers 34, 36 are changed in frequency by means of mixers 93, 94 and a local oscillator 95 and are taken to the input terminals of a hybrid 98 which in normal operating conditions, with only one receiver giving output, provides equal inputs to two power amplifiers 91, 92. The outputs of these amplifiers are connected to the input probes 30<SP>1</SP>, 32<SP>1</SP> of an aerial structure and waveguide coupling, of the kind described with reference to the second embodiment, which is used for transmission. A current supply source 99 may supply a coil structure 42 through a switch 100 with alternating currents in quadrature so that a rotating linearly polarized wave is transmitted from the aerial structure 10<SP>1</SP>. Alternatively, by applying a control current derived from the output of the phase detector 62, the transmitted wave may be returned in the same direction as the received wave, in a retro-directive arrangement. In a fourth embodiment, the input probes (26), (28), Fig. 5 (not shown) of a transmitting arrangement of the kind shown in Fig. 1 are supplied through controllable phase-shifters, so allowing the direction of the transmitted wave to be changed as desired. In a fifth embodiment, Fig. 6 (not shown), a receive-transmit system utilizes identical arrangements of the kind shown in Fig. 1 which are connected together through receivers, frequency changing equipment and power amplifiers. By appropriately orienting the receiving and transmitting aerial structures with respect to each other, retro-directivity may be obtained.