Patent GB-1070534-A (GB)
Title: Radio beacon
Inventor: EARP CHARLES WILLIAM
IPC: G01S1/02
Filed: 1963-05-13
Abstract: 1,070,534. Aerials; radio navigation. STANDARD TELEPHONES & CABLES Ltd. May 8, 1964 [May 13, 1963], No. 18870/63. Addition to 1,053,382. Headings H4A and H4D. A radio glide path beacon comprises a vertical linear array of aerials and means to simulate oppositely phased movements along the array of two sources of carrier waves of equal frequency and of opposite radio-frequency phases. In the embodiments the fact that horizontallypolarized waves reflected from the earth are 180 degrees out of phase with the incident waves is utilized. Aerials A 1 , A 2 , A 3  at respective heights above ground of H, 2H and 3H (Fig. 1) are energized in cyclic succession by anti-phased outputs " + ", " - ") of a V.H.F. transmitter according to a coupling step sequence:- the super-scripts arising from images A<SP>1</SP> 1 , A<SP>1</SP> 2 , A<SP>1</SP> 3 . and coupling steps 1 and 7 being equivalent to a hypothetical aerial A, at ground level being energized simultaneously with the anti-phased transmitter outputs, i.e. no effective energization. The ensuing field at a distant point comprises amplitude-modulation (A.M.) sidebands at the switching frequency F and its odd harmonics (Fig. 2). An additional and continuous wave of the same radio-frequency is made from one or more of the aerials to afford amplitude-demodulation of the sidebands. An aircraft receiver indicates quantity and sense of imbalance between received F and 3F sidebands, the desired glide path being in this case at an elevation of 2À6 degrees. Or for a glide path at some five degrees the amplitude comparison is made between 3F and 5F sidebands, etc. The coupling sequence can be modified by energizing aerial A 3  for two successive time intervals. An alternative arrangement of aerial heights is that in which the heights are H/2, 3H/2 and 5H/2. The aerials may be vertical slots in a vertical cylinder in the case where the azimuthal sector coverage need not exceed 180 degrees. An embodiment wherein fundamental 90 c/s. and 150 c/s. sidebands are produced simultaneously and wherein unwanted higher-order sidebands are reduced is described (Fig. 4): an electronic distributer incorporating bridge networks (X, Y, Z) (each comprising three #/4 lines and one 3 ),/4 line and the Z-bridges isolating the X- and Y-bridges from one another) and shunt switching diodes (a) causes simulation of four pairs of correlated oppositely-moving radio sources. X-pulses are fed to X-bridge diodes at 150 c/s. and Y-pulses to Y-bridge diodes at 90 c/s. For amplitude-demodulation of the sidebands at the distant receiver additional aerials (15) are coupled directly to the transmitter (11). The whole aerial system is constituted by a vertical array of vertical slots cut in a hollow metal cylinder of a diameter of some #/3. The coupling schedule is described in detail in the Specification. The net resultant fields are described (Fig. 7). An alternative embodiment is described utilizing fifteen aerials at height intervals of 1À6# with coupling sequences based on frequencies of 50 c/s., 18 c/s.; the ensuring distribution at 150 c/s. and 90 c/s. is illustrated (Fig. 8): since there is insignificant energy below <SP>5</SP>/ 8  degree elevation the effect of reflections from obstacles is reduced.