Patent GB-583480-A (GB)
Title: Apparatus for tracing radiation patterns produced by aerial systems for the transmission of radio waves and thereby facilitating the design of directional aerial arrays
IPC: G01R29/10
Filed: 1943-11-03
Abstract: 583,480. Measuring ; directive radio systems. TELEPHONE MANUFACTURING CO., Ltd., and SARAGA, W. Nov. 3, 1943, No. 18178. [Class 40 (v)] Apparatus for use in predetermining the radiation patterns of aerial arrays comprises means for producing a number of phase modulated carriers to simulate the field contributions due to individual elements of the array, the amplitude modulation envelope of the sum of the carrier voltages which represents the variation of field strength observed by a receiver moving around the array being displayed on a cathode ray oscillograph on a polar co-ordinate or other suitable time base which operates at the modulation frequency. For an array of a number of omnidirectional aerials in which the current in the ith aerial is ai Sin (#0t - alphai), the field at a point P remote from the system due to the ith aerial is given by Ei =Tai Sin[#0t -alphai+Bi cos (#-#i)] where Bi is 2# times the distance ri expressed in wavelengths of the i-th aerial from the origin of the co-ordinate system and # and #i are the bearings of the point P and the i-th aerial from the origin with respect to a zero direction. T is a constant, and the phase change due to the distance of P from the origin is neglected as it is common to all aerials of the array. If # is replaced by #t, where # is small compared with #0 the expression Ei=Tai sin [#0t - alphai+#i cos(#t - #i)] represents a sinusoidal oscillation of frequency #0 / 2#, phase modulated by a sinusoidal oscillation of frequency # /2#, one cycle of modulation representing the variations in phase of the field due to the i-th aerial as point P is moved completely around the array. In the apparatus shown in Fig. 3 each aerial is simulated by an '' aerial unit " which produces a phase modulated carrier. The value of the carrier frequency employed is not important and a suitable oscillator of pulsatance 0 is employed. The carrier input to each phase modulator is adjusted by an attenuator and a phase shifter to have the desired amplitude and phase a1, alpha1, alpha2, alpha2, &c. to simulate the energization of the , various aerials such as a1 sin (#t - alpha1). The modulation is supplied from an oscillator of pulsatance #, lower than # and may be replaced by A.C. mains. The amplitude and phase of the modulation input to each modulator is also adjusted by an attenuator and phase shifter to the values appropriate to the polar co-ordinate of the aerial such as r1, #1, &c. so that the modulated output represents the contribution of field strength from the aerial, such as Ta, sin [#t - alpha1 +#1 cos (#t - #1,)] in the case of aerial 1. The sum of the outputs from the modulators representing the resultant field strength from the array #n E=R##ai sin [#t -alphai + #i cos (#t - #i)] #i-1 is obtained by adding the individual outputs, which are maintained of constant amplitude, in series. The combined output is amplitude modulated and is fed through an amplifier to a,detector which extracts the amplitude modulation, the fundamental frequency of which is #/2# or an integral multiple of it. This resultant voltage A(#t) which represents the variation of E as point P moves around the array may be displayed on a cathode ray oscillograph as a function of #, as deflection on a linear or other time base synchronized with the modulation #. Preferably, however, as shown in Fig. 3 the function A(#t) is displayed on a circular time base so that the radiation pattern is delineated in polar coordinates. The modulation voltage b0 cos #t is fed through a 90 degree phase splitter to a modulator unit which is also fed with A(#t) and thence to the two pairs of plates of the cathode ray tube. The two components B0 sin (#t+#) and B0 cos (#t +#) modulated with the amplitude of A(#t) or A(#), namely B1[1+m]A#1] sin (#t+#) and B1[1+m]A#1] cos (#t+#) produce a trace on the oscillograph screen in which the radiation pattern A(#) is displayed in polar co-ordinates with a circular zero line, Fig. 4 (not shown). In order to display the pattern 'on conventional polar co-ordinates with zero at the origin the carrier terms have to be suppressed in the output of the modulator unit. This suppression may be obtained by any known means such as the use of two identical modulator units, Fig. 5 (not shown), only one of which is fed with the signal A(#), the outputs being combined in opposition so that only the terms B1m|A# sin (#t+#) and B1m| A#| cos (#t+#) are applied to the deflecting plates of the oscillograph. The carriers may also be suppressed by adding the carrier input voltages with suitable amplification to the respective modulated output voltages in opposition. The " aerial unit " for the first aerial and the modulation frequency phase shifter for the second aerial can be dispensed with if the coordinates of the system are so chosen that the first aerial is at the origin and the second aerial lies on the zero reference bearing. Such an arrangement for two aerials is illustrated in Fig. 7 (not shown) in which the effect of aerial 1 is produced -by pure carrier injected in series with the output of the modulator corresponding to aerial 2. The detector which extracts the modulation A(#t) or A(#) from the combined outputs of the "aerial units " can be dispensed with, in which case the expression E is traced on the screen of the oscillograph and the radiation pattern is defined by a bright traced area... The apparatus may be employed to trace the radiation pattern of an aerial system at an angle # from the plane containing the elements of the array by multiplying the distances between the aerials by a factor of cos #. This can be done by means of a potential divider connected between the output of the modulation frequency (#/2#) source and the signal inputs to the aerial units. As the total radiation from an elementary aerial also decreases with angle of elevation a potential divider with a suitable characteristic is also inserted at the output of the carrier frequency (#/2#) oscillator and is ganged with the first potential divider.