Patent GB-541669-A (GB)
Title: Directional antenna systems
IPC: H01Q3/30
Filed: 1940-06-21
Abstract: 541,669. Directive wireless systems. STANDARD TELEPHONES & CABLES, Ltd. June 21, 1940, No. 10709. Convention date, Aug. 2, 1939. [Class 40 (v)] In an antenna-array system of the Friis type which is steerable, in the sense that the direction of maximum reception can be varied in a vertical or a horizontal plane as described in the Bell System Technical Journal for July, 1937, a modulator located at each aerial feeds back to a 'terminal station, over a relatively low-grade line, an intermediate-frequency equal to the difference between the frequency of the signals and that of waves received over a high-grade line from an oscillator at the terminal station. Steering is effected either by remote control of phasechangers or by varying the frequency of the oscillator. The array may be set by means of remotely controlled switches to select one of several frequencies, and may be adapted to combine the radiation received simultaneously from two different directions or to select automatically the direction which gives the best reception at the moment. In the arrangement shown in Fig. 9 each aerial, such as A2, is provided with a modulator, such as M2, which intermodulates the signal frequency received from the aerial with the oscillator frequency received from the oscillator BO through the high-grade high-frequency feeder LO, which may be of the co-axial type and is common to all aerials, and delivers the difference frequency to the common line Li which may be an open-wire line and feeds the intermediatefrequency amplifier IFA of a superheterodyne detector. It is shown in the Specification that, in the absence of phase-changers such as PC2, if the inter-aerial distances are equal to one another in space and along the feeder, the phase-difference between the intermediate-frequency products of two adjacent aerials, as received at the terminalstation amplifier IFA is proportional to where I is the intermediate frequency, S is the signal frequency, d is the angle of arrival of the radiation, and the positive or negative sign is taken for S according as the oscillator frequency is greater or less than the signal frequency. The constant term 21 in this expression is eliminated by a preliminary setting of phase-changers PC1, PC2 ..., and the angle of maximum reception is then varied by co-ordinated adjustment of these instruments by remote control, Fig. 15 (not shown). The array may be adapted to use two or more different frequencies, and one modulator such as M2, M4 is provided for each frequency at each station, and selected by means of a remotely controlled three-armed switch 10. The phase-changers PC1, PC2 ... may be removed from the line Li<SP>1</SP>, in which their effects are cumulative, and connected in the leads between it and the modulators, where their effects are independent of one another, Fig. 8 (not shown). Fig. 7 (not shown) illustrates a system in which the phase-changers are located at the terminal station and are connected to the modulators by separate intermediate-frequency lines Li. Alternatively the system may be steered by varying the oscillator frequency, since the phase-difference between the modulator outputs reaching the terminal station from two adjacent aerials is proportional to where O is the oscillator frequency, S the signal frequency and d the angle of arrival of the radiation, so that for a given value of d the-contributions of all the aerials will arrive in phase if the frequency 0 is properly chosen. The intermediate frequency also will vary as the oscillator frequency O varies, but the fixed intermediate frequency required for the superheterodyne receiver can be obtained by intermodulation with the output of a second or tuning oscillator, which is retuned simultaneously with the steering- oscillator. The need for retuning a tuning oscillator can be obviated, Fig. 11 (not shown), by reproducing the signal frequency at the terminal station as a summation product of the intermodulation of the intermediate frequency from line Li with the steering frequency from the local oscillator. In a diversity system, Fig. 12, it is possible to select the best of two signals having different arrival angles or different frequences or both. In this arrangement a steering oscillator SO is associated with a high-frequency line LO, a pair of out-station modulators M2, M4 used for two different frequencies at each aerial, an intermediate-frequency return line Li, a terminal modulator M1 for reproducing the signal frequency, and a short-wave receiver 33, while a second steering-oscillator SO1 is associated with corresponding parts LO1, LI1, M6 and M8 at each aerial, M2 and 34. The modulators appropriate to the desired signal frequencies are selected by means of the remotely controlled switches 10, 101, and the signals received from two different angles of arrival, as determined by the frequencies of the steering-oscillators, are detected by the receivers 33, 34 whose outputs are in part fed differentially, after rectification, to a relay 37 which connects the telephones T to the set receiving the stronger signal. Alternatively, Fig. 12A (not shown), the outputs of the receiving- sets may be added together after phase-adjustment. The design of the modulators may be as illustrated in Fig. 13 (not shown). Remote control of switches. The three-armed switches shown in Fig. 9 have their arms mounted on a shaft carrying a disc such as 26, Fig. 14, for each position of the switch. Each disc has a wiper connected by a separate line to a switch located at the terminal station and operated by a button such as 20 associated with a locking-bar 23. When a button is pressed, the shaft is turned by motor 25 until the wiper reaches an insulating segment on the corresponding disc.