Patent GB-1141357-A (GB)
Title: Radio navigation system
IPC: B64F1/18
Filed: 1966-03-11
Abstract: 1,141,357. Radio beacon systems. INTERNATIONAL STANDARD ELECTRIC CORP. 11 March, 1966 [18 March, 1965 (2)], No. 10808/66. Heading H4D. A radio beacon radiates a fan beam by applying a signal having components with frequencies continuously extending from fu to fo to a linear array antenna which radiates energy in a direction proportional to the frequency of the energy. At the beacon receiver therefore the angle of incidence within the beam may be ascertained by determining the frequency of the signal having the maximum amplitude. Figs. 1 and 2 show respectively the plan and elevation of a 90-degree vertical fan beam rotated in azimuth and produced by the transmitter of Fig. 3. The signal having the components extending in frequency from fu to fo is produced by passing the output of a noise generator 1 through a band-pass filter 2 of the said bandwidth. All the frequency components have the same amplitude. The filter output is code modulated in 3 by means of a coding device 4 coupled to the antenna 6 azimuth rotation axis whereby by a decoding process the user of the beacon receiver is able to determine the azimuth of the beam. At the beacon receiver, Fig. 4 (e.g. on an aircraft) the beam is received as it sweeps past at a maximum amplitude frequency (fi), Fig. 6, representing the elevation, and with a coding representing the azimuth. The received signal is converted to an 1.F. signal in mixer 13 and is fed to an I.F. amplifier 14 able to pass all the expected frequencies. The output of the amplifier is fed to a narrow band pass filter 16 having its pass frequency varied from the lower limit representing 0 degrees elevation to the highest limit representing 90 degrees elevation. At the lower limit a start pulse is fed via pulse former 17 to start a counter 18. When circuit 17 detects a signal of maximum amplitude a stop pulse is thereby fed to the counter, thereby stopping it such that its count represents the elevation which may be evaluated and displayed on device 19. Alternatively the output of amplifier may be fed to the Y deflector plates of a C.R.T. and a signal proportional to the frequency may be applied to the X plates. A display such as Fig. 6 is then produced and the X axis can be calibrated in elevation. The output of amplifier 14 is fed to a decoding arrangement 20 and 21 to determine the azimuth. In further embodiments, Figs. 7- 14, the antenna, Figs. 7-9, comprises a primary linear array radiator 32 aligned along the focal axis of a planar parabolic reflector 31. This produces a fan beam in the plane of the primary array and angularly extending on either side of the central axis of the antenna about which it is rotated, by amounts depending on the upper and lower frequency limits of the applied energy. In the beam of Figs. 10 and 10A for example (10 is lateral view and 10A is view down axis of rotation) said frequencies are such that the beam extends equal amounts either side of the rotation axis. The beam is rotationably coded. The angular extent of the beam may vary with its rotation such that the volume of space swept by the beam may have a wedge shape-Figs. 11 to 13 (not shown). The necessary variation of the upper and lower frequency limits of the radiated energy is controlled in dependence on the detected rotation angle of the beam, Fig. 14 (not shown).