Patent GB-596391-A (GB)
Title: Radio beacon
IPC: H01Q21/22
Filed: 1945-01-12
Abstract: 596,391. Directive radio systems. STANDARD TELEPHONES & CABLES, Ltd. Jan. 12, 1945, No. 1062. Convention date, Nov. 15, 1943. Drawings to Specification. [Class 40 (v)] A directive radio beacon system comprises a first antenna supplied with modulated carrier energy through an adjustable phase control and a second antenna supplied with sideband energy only, also through an adjustable phase control, the controls being jointly adjusted to maintain a predetermined phase difference between the energizations and to control the parasitic effect between the antennµ in such manner as to increase the rate of change of amplitude of the beacon sideband radiation pattern with respect to polar angle, in a predetermined direction. The second antenna may be either a single radiator or a plurality of radiators arranged in line with the first antenna and in unsymmetrically spaced relation with respect thereto, each having its own controlling means for adjusting the phase and amplitude of the energy radiated.' Considering the most usual case in which the sideband energization of the radiators to one side of the first antenna leads by 90 degrees and that on the other side lags by 90 degrees, it is shown that, for a linear array fed as above stated the total field at any point on a line at an angle # to the perpendicular through the " carrier " unit of the array is proportional to two sets of components in quadrature. One of these sets consists of terms rm sin (dm sin #) where " rm " is the strength of the radiation from radiator rm and dm its distance from the first antenna. The other set consists of corresponding terms rm cos (dm sin #). With a symmetrical antenna system these latter terms, which do not add appreciably to the sharpness of the pattern in the vicinity of the perpendicular course line, cancel out. For an unsymmetrical array however they only partially cancel and thus normally dull the course. So far it has been assumed that the individual antenna are omnidirectional, that is that "rm" is independent of #; however, due to the parasitic excitation produced by inter-antenna coupling, this is not the case and by altering the phase of the parasitic currents by jointly adjusting the phase controls, maintaining the radiated energy phase differences constant, rm can be made approximately proportional to sin # near the course. In such conditions the sine set of terms referred to relate the total field at angle # to sin2 # and the cosine set relate it to sin #, thus giving a very sharply defined course from an unsymmetrical array. Unsymmetrical beacon systems comprising arrays of two, three and six antennµ are described with reference to Figs. 2, 5 and 8 (not shown) by way of example. Equisignal overlapping beam course lines are obtained either by providing keying means for alternately reversing the phase of the energy supplied to the second antenna or antenna array or by providing two modulating tones, modulating the carrier separately with these and applying the resulting signals to opposite points of a bridge network supplying the antennµ with the sum and difference thereof respectively. It is stated that if a portion of the second antenna system is arranged to form a symmetrical group about the first antennµ and inside the unsymmetrical part of the array the clearance between the minor lobes of one overlapping pattern and the nearest point of the other may be increased. Specifications 563,007 and 592,571 are referred to.