Patent GB-666455-A (GB)
Title: Improvements in or relating to ultra-high frequency radio signalling systems
Inventor: EVANS JOHN MICHAEL THOMPSON
IPC: H01Q15/00
Filed: 1949-10-25
Abstract: 666,455. Directive radio signalling. GENERAL ELECTRIC CO., Ltd. Oct. 4, 1950 [Oct. 25, 1949], No. 27429/49. Classes 40 (v) and 40 (vii). A high-frequency radio system for two-way point-to-point communication comprises at each station a prismatic refractory device having a refractive index which is variable with frequency elevated above ground level and an aerial system comprising a transmitting aerial disposed at ground level adapted to transmit a narrow beam of radio energy toward the prismatic device and a receiving aerial also at ground level for receiving a narrow beam of waves transmitted from the second station, the prismatic device being disposed so that the transmitted beam is refracted towards a similar prismatic device at the second station and a beam received by the prismatic device from said similar device is directed towards the receiving aerial; the frequencies of the transmitted and received beams being different. In a system in which an intermediate repeater is used the transmitter 1 at the first station feeds a directive aerial 3 radiating a beam of radio wave towards refractory device 6, at which the beam is refracted and directed towards a similar elevated refractory device 20 at the repeater station which directs the beam downwards to the ground level receiving aerial 18. The signals received by aerial 18 are passed to translating system 14 where the carrier frequency is changed to a relatively low value, the signal amplified, and then retransmitted on a high-frequency carrier from directive aerial 16 through prism 21. The beam refracted by prism 21 is directed towards elevated prism 12 at the second terminal station which refracts it downwards to receiving aerial 11 feeding receiver 9. For signalling in the opposite direction, using the same prisms 12, 21, 20 and 5, use is made of transmitting aerials 10 and 17, receiving aerials 19 and 4 and repeater transceiver 15. The prismatic device and aerial at each point are preferably arranged so that the angle through which the beam is deflected by the prism is approximately the angle of minimum deviation for waves of the frequency of the beam; in such an arrangement small variations in prism location due to the effect of wind or the like have least effect. In the embodiment described the frequencies of the go and return paths are different and due to the variation of the refractive indices of the prismatic devices with frequency this enables the radiating and receiving aerials at a given point (e.g. 3 and 4) to be spaced apart as waves being sent and received from the same direction are diffracted through different angles. It is stated to be known to use elevated plane reflectors in place of the prismatic devices of the present invention. In using such reflectors it is necessary to arrange that the angles through which the transmitted and received beams are deviated differ slightly. This necessitates the provision of two effective reflecting surfaces and, to ensure the beams are reflected by the correct surface, they have to be differently polarized. The prismatic devices may consist of a plurality of parallel rectangular metal plates equally spaced and having equal lengths but progressively decreasing widths and being symmetrical about a plane passing through all the longitudinal axes of the plates. Fig. 2 (not shown). An alternative arrangement consists of a plurality of identical parallel metal plates each in form of an isocseles triangle, the plates being equally spaced and the device symmetrical about a plane passing through the bisector of the angle at the apex of the plates, Fig. 3 (not shown).