Patent GB-684313-A (GB)
Title: Improvements in systems for guiding dirigible craft
IPC: G01S5/12
Filed: 1948-09-10
Abstract: 684,313. Radio-navigation. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AERONAUTIQUES. Sept. 10, 1948 [Sept. 23, 1947; July 20, 1948], Nos. 23866/48 and 23867/48. Class 40 (vii). A radio-navigation system, enabling a craft to determine its distance from a fixed point and its deviation from a predetermined course-line, comprises a beacon station at the fixed point transmitting bearing-dependent radio signals, and, on the craft, two spaced aerials receiving signals which are compared to determine the distance of the craft from the beacon, and a further aerial, the signal received by which is compared with one or both of the signals received by the other two aerials to determine the deviation of the craft from a predetermined course line passing through the beacon. First embodiment, Figs. 1 and 2. A beacon 2 situated upon a runway 1 and defining a course line Ox in the direction of the runway radiates a continuously rotating radio beam, and also transmits a reference signal at a predetermined angular position of the beam. An aircraft 3 comprises two aerials A and B mounted on the wing-tips. The signals received by these aerials (shown as 4, 4<SP>1</SP> in Fig. 2) are amplified and detected by respective circuits 5, 6, 7 and 5<SP>1</SP>, 6<SP>1</SP>, 7<SP>1</SP> (which both include pulse-deriving apparatus as described in Specification No. 691,294, combined in mixer circuit 8 and applied thence to the intensity-modulating electrode or vertical-deflecting plates of a cathode-ray tube. The reference signal is received by auxiliary aerial 13 and triggers a time-base circuit 15 providing a sweep waveform which is applied to the horizontal-deflecting plates of the cathode-ray tube. The signals received by aerials 4, 4<SP>1</SP> produce two indications upon the horizontal trace; the point mid-way between these indicates the deviation of the craft with respect to the course-line Ox while (as described in Specification 684,088) their spacing apart indicates the distance of the craft from the beacon 2. In a modification of this embodiment, Fig. 5 (not shown), the reference pulse triggers two Eccles-Jordan circuits which are also controlled by respective outputs from the spaced aerials A, B, thus giving pulses whose lengths correspond to the timing of the beam as it passes the aerials A and B respectively. These pulses are applied in aiding and opposing relationships to two galvanometers which indicate the deviation from the course-line and distance from the beacon respectively. Second embodiment, Fig. 8. The beacon 89 transmits a stationary radio beam having a radiation pattern 91. The signals received by aerials A and B on aircraft 92 have amplitudes proportional to Oa and Ob respectively and are equal when the aircraft is following the course line Ox. For measuring deviation from the course-line, either the difference between the signals received by aerials A and B is measured, in which case automatic-volume-control to eliminate the effect of distance upon signal amplitude is necessary, or, preferably, the ratio of the amplitudes of the signals received is determined. In order to measure the range to the beacon, the amplitude of the signal received by a further aerial C is compared with that of the signal received by either of aerials A and B when the course is being followed. Third embodiment, Fig. 10. The beacon radiates a continuously rotating beam 50 and a reference signal when the beam-axis lies along a predetermined direction (indicated by the angle y) with respect to the course line Ox. The receiving apparatus comprises means for generating a pulse when the. signals received by aerials A and B are of equal amplitude and a cathode-ray tube having a horizontal sweep triggered by the reference signal and to which the pulse is applied to produce an indication showing the deviation of the craft with respect to the course-line. Further apparatus also produces a pulse when the signals received by either aerial A or B and a centrally-situated aerial C are of equal amplitude. This pulse is also applied to the cathode-ray tube, the spacing between the indications measuring the distance of the craft from the beacon. In an alternative arrangement, pulses are derived by comparing the signal received by aerial C with those received by each of aerials A and B, the spacing between the corresponding indications on the cathode-ray tube measuring range and the midpoint between the indications indicating deviation from the course-line. Fourth embodiment, Fig. 12. The beacon comprises a frequency-sensitive directional aerial so that signals of radio-frequencies f 0 , f 1 , f 2  applied thereto are transmitted with radiation patterns as indicated. The signal applied to the beacon aerial may either be periodically varied in frequency so that the radiated beam performs an oscillating motion or comprise a band of frequencies resulting in a radiation pattern in which the radiated frequency varies with azimuth. Receiving apparatus placed at A, B and C on an aircraft and tuned respectively to frequencies f 1'  f 2'  f 0  develop signals whose amplitudes depend upon the distance and azimuthal position of the craft; these signals are compared by apparatus similar to that described with reference to Fig. 8 to determine the range and deviation of the craft from the glide path.