Patent GB-1245885-A (GB)
Title: Improved radio range navigation system for aircraft
Inventor: REDLICH R W
IPC: G01S1/50
Filed: 1969-05-22
Abstract: 1,245,885. Radio navigation systems; aerials. SYDNEY, UNIVERSITY OF. 22 May, 1969 [24 May, 1968], No. 26094/69. Headings H4A and H4D. In a compatible omnidirectional VOR aircraft navigation system emitting reference omnidirectional and rotary variable phase signals from which an aircraft can determine its bearing from the transmitter in terms of the phase difference of the demodulated signals, a reference phase signal is transmitted as sinusoidal 30 Hz AM upon a carrier, while the variable phase signal is phase locked to the latter and transmitted as a square wave 30 Hz FM upon a carrier equal to the reference carrier frequency Œ9960 Hz, to develop a 9960 Hz FM subcarrier by heterodyning of the variable phase signal with the reference phase carrier. The variable phase signal is derived by radiating a first and a second Fourier component of a square-wave frequency modulated signal from a first and a second concentric antenna array; the modulation being equivalent to 30 Hz switching of carrier between frequencies of carrier Œ480 Hz. A reference transmitter 20 (Fig. 1) generates a reference phase carrier of frequency fr controlled by AFC 25 which is AM with frequency 30 Hz to excite hybrid rings 22, 23 feeding spaced inner antenna elements A, B, C, D (Fig. 2A) to transmit a 30 Hz AM omnidirectional field as phase reference. A variable phase transmitter 24 operates a carrier of fr + 9960 Hz controlled by AFC 25 which is suitably attenuated at 26 to energize balanced modulators 27 28 for AM according to functions (cos 960#t) and (sin 960#t) respectively. The output of modulator 27 energizes one side of each of hybrid rings 29, 30 feeding plural loop antennµ 1 to 12 concentric with antennµ A, B, C, D in phase to generate an omnidirectional field pattern. The output of the second modulator is phase delayed at 31 to lag #/2 the output of the first network and is applied to balanced modulators 32, 33 for further AM according to respective functions (cos 60#t) and sin (60#t). The outputs are supplied to the remaining sides of hybrid rings 22, 23 feeding antenna elements A to D and are shown to constitute first Fourier components sin #, cos # of an approximately SQUARE WAVE SIGNAL. The output of the second modulator 28 is also 1 : 3 attenuated at 34 and applied to balanced modulators 35, 36 for AM according to functioning (cos 180#t) and (sin 180#t); the outputs being fed to the remaining sides of the respective hybrid rings 29, 30 supplying the antenna elements 1 to 12; and are shown to constitute the second Fourier components sin 3#, cos 3# of the approximately SQUARE WAVE SIGNAL. The radiation patterns of the antenna arrays (Figs. 3A, 3B) transmitted simultaneously generate rotating fields composed of sin #, cos #; sin 3#, cos 3# functions, and combine to produce the rotating field of a variable phase signal frequency modulated by an approximately square waveform signal. A mathematical analysis is given, and it is shown that approximation to square wave frequency modulation is produced by the combination of the first two terms of the Fourier expansion of the unit square wave (Figs. 4A to 4D, not shown). The inner array A, B, C, D (which may be a standard VOR slot) radiating sin # and cos # signals is thus energized by a reference signal fr AM at 30 Hz and by cos # signal 4/# sin 2# /f D  t sin 960 #t cos 60#t and sin # signal 4/# sin 2# f D  t sin 960#t sin 60#t while the outer array of Alford loops 1 to 12 located on a circle of circumference 3# are energized by omnidirectional reference phas signal cos 2#f D  t cos 960# t and by cos 3# signal -4/3# sin 2# f D  t sin 960# t cos 180# t on loops 1, 3, 5, 7, 9, 11 and by sin 3# signal 4/3# sin 2#f/ D t sin 960# t sin 180# on loops 2, 4, 6, 8, 10, 12 with omnidirectional reference phase signals simultaneously on loops A to D; the frequency f D  =fr + 9960 Hz developing the receiver sub-carrier of 9960 Hz by heterodyning.