Patent GB-1062551-A (GB)
Title: Radio guidance systems
Inventor: EARP CHARLES WILLIAM
IPC: G01S1/02
Filed: 1963-04-26
Abstract: 1,062,551. Aerials; radio navigation. STANDARD TELEPHONES & CABLES Ltd. April 24, 1964 [April 26, 1963], No. 16555/63. Headings H4A and H4D. In a course line or glide path equisignal beacon utilizing two overlapping directive radiation diagrams carrying different modulation frequencies (90 c/s., 150 c/s.) for defining the desired flight path and also utilizing " clearance " signals radiated additionally for conveying directional information outside the overlapping directive diagrams, errors arise from obstacle reflections and known systems utilize a carrier frequency for the clearance signals differing by some 10 kc/s. from that of the main signals. According to the present invention the clearance signal carrier wave is amplitude modulated by at least one signal in phase quadrature with one of the signals modulating the carrier wave in the two overlapping diagrams. The same carrier frequency (wavelength #) is used in the embodiments. Azimuth approach beacons.-In one embodiment the clearance signal radiation (Fig. 3A, not shown) is composed of one pattern (7) representing carrier-plus-sideband radiation and additional patterns (8, 9) representing sidebands only the phases of the modulating signals being in quadrature with those in the respective overlapping diagrams (5, 4, Fig. 2, not shown). Aerial arrays utilizing elements spaced 3#/8 apart and elements 3#/4 apart (Figs. 4A, 5A, not shown) are outlined, a reflecting screen #/4 behind the arrays being utilized in each case. The clearance signal carrier wave may be in phase quadrature with that appertaining to the overlapping diagrams A beacon, Fig. 8, includes a carrier source 25, power dividers 30, 35, 36, a balanced modulator 26, bridge networks having three sides #/4 long and the side marked " X " 3#/4 long, and a linear aerial array 27. Sidebands are combined with the carrier in bridge networks. The sideband-only main signals to the aerial array for the overlapping diagrams, with relatively opposite R.F. phases of the sidebands, are radiated from elements 27A ... 27E and 27F ... 27J respectively. A combined carrier-plus-sidebands (CSB) signal is fed from bridge 31 via a transmission line 37, adjusted such that the CSB signal is fed to all radiating elements with R.F. phase of 0‹, and via bridge 34 to power dividers 35, 36. The clearance signal radiation is as follows: sidebands at 90 c/s. and 150 c/s. from terminals 29Q, 28Q, having envelopes in phase quadrature with those from terminals 29, 28, are combined in bridge 38, the sidebands being in anti- R.F. phase at corner G. The sidebands at G are combined with the clearance signal carrier in bridge 32 to form a CSB signal fed to comer K of bridge 41 the corner J of which is fed with the sidebands from corner F of bridge 38 via a power reducer 40. The remaining corners of bridge 41 are connected to further bridges 44, 45. Elements 27E, 27F are thereby fed with oppositelyphased clearance sideband signals. The clearance CSB signal is fed via transmission line 42 to bridge 41, the line length being such that the clearance CSB signal does not tend to cancel the main CSB signal. The ensuing total radiation from the beacon in addition to the overlapping diagrams (4, 5, Fig. 2, not shown), consists of clearance signal radiation in the form of two sideband-lobes on opposite sides of the course line and a single broad CSB lobe symmetrical thereabout. Glide path beacon.-Clearance is not provided above the glide path since aircraft are said to normally approach from below it. The aerial system (Fig. 7, not shown) comprises a vertical stack of seven elements at heights of 5#, 6#, 7#, 12#, 15#, 18# and 21#; the signals fed to respective elements are detailed, together with the ensuing resultant radiations (Figs. 7A, 7B, not shown).