Patent GB-1053232-A (GB)
IPC: G01S1/02
Abstract: 1,053,232. Aerials; radio navigation. STANDARD TELEPHONES & CABLES Ltd. April 24, 1964 [May 1, 1963], No. 17173/63. Headings H4A and H4D. Relates to radio glide path beacons which radiate a pair of partly overlapping radiation patterns; the invention provides. for the radiation of two sets of additional signals: "clearance" signals which afford a broader directional coverage than the main signals and ."shaping" signals which modify the main (" main shaping ") and clearance (" clearance shaping ") signal radiation patterns such that the main and clearance signals are enhanced over certain ranges of angular deviation with respect to the glide path and are reduced at others. The effects of reflection and scatter, e.g. by hills and trees are thereby reduced. The radiations are of two general types herein referred to as P and Q: type P consist of the sidebands only of a V.H.F. carrier amplitudemodulated equally at frequencies of 90 c./s. and 150 c./s., and type Q consist of the carrier and the sidebands of such amplitude modulation; the emissions are further sub-divided as follows :- Type P 1 : R.F. and modulation frequencies . of reference phase. Type P 2 : as for P 1  except that R.F. phase is opposite thereto. Type P 3 : as for P 1  except that modulations are in phase quadrature therewith. Type P 4 : as for P 2  except that modulations are in phase quadrature therewith. Type Q 1 : 150 c./s. modulation in opposite phase to that in P 1 . Type Q 2 : as for Q 1  except that R.F. phase is opposite thereto. Type Q 3 : as for Q 1  except that modulations are in phase quadrature therewith. Type Q 4 : as for Q 2  except that modulations are in phase quadrature therewith. Main signals of type P 1  are radiated according to a pattern 1, Fig. 1 (not shown), and shaping signals of type P 2  of 62% of the amplitude of those in pattern 1 are radiated according to a pattern 2 thereby affording a resultant " main sidebands-only " (main SBO) radiation pattern 3. Main signals of type Q 1  are radiated according to a pattern 4, Fig. 2 (not shown), and shaping signals of type Q 2  of 33% of the amplitude of those in pattern 4 are radiated in a pattern 5, Fig. 2, to yield a resultant " main carrierplus-sidebands " (main CSB) radiation pattern 6, Fig. 5 (not shown). Clearance signals, of types P 3 , P 4 , Q 3  and Q 4 , are radiated to yield a resultant clearance SBO pattern 9, Fig. 3 (not shown), and a resultant clearance CSB pattern 12, Fig. 4 (not shown). 90 c./s. modulation predominates above the glide path and 150 c./s. modulation below it. Fig. 6 (not shown) shows percentage difference in depth of modulation (DDM) against angle of elevation. In regions much above and below the glide path the aircraft receiver output corresponds to the clearance signals. The reduction of the effect of reflections is described with reference to Fig. 7 (not shown). Aerials, Fig. 8 (not shown).-The aerial array consists of twenty half-wave elements in groups of eight, two, eight, two about mean heights of H, 2H, 3H and 4H respectively where H is 5.73 times the wavelength (#) for a 2.5-degree glide path. The element separation in a group is 3#/4. The existing transmitter power of 80 watts can be reduced to 10 watts thereby permitting transistorized R.F. amplifiers. To compensate for losses in bridge circuits between the transmitter and aerial a corner reflector may be added to each radiating element.