Patent GB-623187-A (GB)
Title: Improvements in or relating to systems for the radio-electric guiding of aircraft
IPC: G01S1/02
Filed: 1946-04-05
Abstract: 623,187. Radio navigation. SOC. FRANCAISE RADIO-ELECTRIQUE. April 5, 1946, No. 10617. Convention date, Feb. 9, 1944. [Class 40 (vii)] A frequency-modulated hyperbolic navigation system, especially applicable to the guiding of aircraft, comprises two aerial systems transmitting waves which are similarly frequency - modulated and of the same mean frequency, and in the craft a receiver wherein the received radiations are combined to derive a beat-frequency which is applied to a frequency-meter. In Fig. 1, a transmitter located at I supplies four aerial systems A, B, C, D. The radiation from the aerials A and B is used to determine, by a predetermined beat-note obtained from the signals received therefrom, the vertical plane through C, D and a runway P. The radiation from aerials C and D defines the distance from the airfield of an aircraft flying in the aforementioned vertical plane, the beat-note obtained varying linearly with distance between D and C. The indication of the frequencymeter is compared with that of an altimeter to define a glide-path for the aircraft, for example, as shown in Fig. 5, where the indicators of the frequency meter 3 and of the altimeter 4 are maintained in alignment. Alternatively signals representative of beat-frequency and of altitude may be supplied differentially to a suitable centre-zero instrument. Specification 575,154 is referred to. The Specification as open to inspection under Sect. 91 describes also means for defining a landing track on an airfield C, D, E, F, Fig. 2, (Cancelled), two transmitters A, B being placed in line with the entrance of the field. The transmissions are frequency-modulated by a sawtooth waveform, the modulations of the two transmissions being displaced in phase by a known amount so that a predetermined beatfrequency is obtained when the aircraft is flying along the line of the centre-track Q. If desired, either of tracks P and R may be defined instead by alteration of the phase displacement. So that the landing may take place from the correct direction, the transmitters are provided with reflectors whereby reception ceases on passing the line A, C, D, B. A hyperbolic glide-path may be defined in the vertical plane by a single elevated aerial system, the direct radiation from the aerial combining with radiation reflected from the surface of the earth to cause the beat-frequency to occur in the receiver. The transmitting aerial may be mounted upon a suitable supporting structure arranged over the entrance to the airfield or may be supported by a balloon. Alternatively, an ultra-violet ray beam may be directed upon a certain point to ionize the air at the point, which is then used as a re-radiator of radio waves directed at it. In a further arrangement for defining a hyperbolic course-line, a single transmitter only is used, the transmitter feeding two aerial systems, one by a connection of short length and the other by a transmission line the velocity of propagation in which is chosen to give the course-line desired. This subjectmatter does not appear in the Specification as accepted.