Patent GB-870916-A (GB)
Title: Improvements in or relating to steerable directional aerial systems
Inventor: MITCHELL GEOFFREY
IPC: H01Q3/26
Filed: 1957-08-15
Abstract: 870,916. Directive aerial systems. POSTMASTER GENERAL. Aug. 15, 1958 [Aug. 15, 1957], No. 25812/57. Class 40(7) A steerable directional aerial system comprises an array of spaced aerials some or all of which are associated into groups, chosen in a particular instance in accordance with the positioning of the aerials and the frequency and direction of arrival of the signal to be received, means for shifting the phases of the outputs of all the aerials associated for the time being in a group by the same amount, and means for combining the phaseshifted outputs. The invention avoids the necessity of providing and adjusting a separate phase shifter for each aerial and it is shown that the output of a grouped arrangement is not seriously below that obtained by individual adjustment for a reasonable number of groups. For example with the aerials positioned so that their distribution density over the array is reasonably close to the average the loss in output with a four group arrangement is less than 1 decibel. Each aerial in the array may be regarded as giving an output represented by a vector and the vectors for all the aerials may be drawn radiating from the same point. If these vectors are divided into groups falling within equal sized sectors, the number of sectors being chosen to correspond with the required number of groups (n), then all the vectors may be moved into one sector by applying to the groups phase shifts of regularly increasing multiples from 0 to (n-1) of 360 degrees/n. Fig. 5 shows an arrangement of p aerials forming an array feeding Q receivers by arrangements according to the invention wherein the aerials are divided into four groups. Each aerial feeds, through an amplifier 4 and a distribution network 5, into Q four-way switches 6. For each receiver like switch outputs are connected by lines to four phase-shifting units 7, 8, 9 and 10 introducing phase shifts of 0, #/2, #, and 3#/2 respectively and the outputs of the four units combined and fed to the receiver. In a modification of this arrangement (Fig. 6, not shown) the aerial amplifiers each feed four phase-shifter units and the output lines from these provide four inputs to banks of four way selector switches, the single outputs from which in each bank are joined and connected to a receiver input. The four-way switches in either of these arrangements requires adjustment to obtain the required aerial groups and must be changed when there is a change of directivity or frequency of the received signal. As considerable calculations are necessary to determine the grouping for all possible service conditions it is preferred to record switch positioning instructions on punched or magnetic tape. Means for setting the switches to group the aerials in accordance with a punched tape record are described with reference to Fig. 7 (not shown). The aerials of the array may comprise inverted cone units formed of 16 wires equally spaced round a 23 feet diameter ring and joined at their lower ends to the inner conductor of an aerial feeder cable. The cone height is made 24 feet 6 inches. An array of fifty to a hundred aerials having an aperture of 300 to 400 metres is contemplated.