MODULATOR FOR INSTRUMENT LANDING SYSTEM

• US 3,675,162 A
• Filed: 07/15/1970
• Issued: 07/04/1972
• Est. Priority Date: 07/15/1970
• Status: Expired due to Term

• Current Assignee: Wilcox Electric Incorporated
• Original Assignee: Akemichi Yamada, Edmund C. Thomas, Edwin J. Martin Jr, James Neal Owen, Raymond Ronald Moberly
• Inventors: Owen, James Neal, Moberly, Raymond Ronald, Martin, Edwin J. Jr., Yamada, Akemichi, Thomas, Edmund C.
• Primary Examiner(s): Brody, Alfred L.
• Application Number:
  US05/055,102
• Time in Patent Office: 720 Days
• Field of Search: 332/42,30,44,45,48,16,23 325/138,49 343/109,107,108
• US Class Current: 342/412
• CPC Class Codes: G01S 1/02 using radio waves G01S19/00 takes precedence

Abstract

A modulator for an instrument landing system includes a source of a radio frequency carrier wave and a first power divider coupling the carrier wave to a first hybrid combining circuit and through a second power divider to first and second constant input impedance audio frequency double sideband suppressed carrier generators with good isolation. The sideband generators are coupled to a second hybrid combining network having a double sideband suppressed carrier difference signal output, constituting a '"'"''"'"''"'"''"'"'sideband'"'"''"'"''"'"''"'"' output of the modulator, and a double sideband suppressed carrier sum output which is combined with the carrier wave in the first hybrid combining circuit to provide a '"'"''"'"''"'"''"'"'carrier wave'"'"''"'"''"'"''"'"' output of the modulator. The sideband generators each include a capacitor bridge, and phase shift means are provided so that the signals on one side of the bridge are reversed in phase with respect to signals on the other side thereof. The bridges are each formed by a pair of spaced parallel stator plates having four facing conductive patterns and a motor driven rotor having a plurality of pie-shaped conductive patterns positioned therebetween. The shape and size of the stator conductive patterns, the number of rotor conductive patterns, and the speed of rotation of the rotor are so selected that a sinusoidal audio frequency modulation of the carrier wave is effected.

Claims

1. In a modulator for instrument landing systems, a first path adapted to receive a radio frequency carrier wave;

first power divider means for dividing the power of said carrier wave in said first path between a second path and a third path while maintaining isolation between said second path and said third path;

second power divider means for dividing the power of said carrier wave in said third path between a fourth path and a fifth path while maintaining isolation between said fourth path and said fifth path;

first constant input impedance sideband generator means modulating said carrier wave at a first audio frequency in said fourth path; and

second constant input impedance sideband generator means modulating said carrier wave at a second audio frequency in said fifth path.

2. A modulator for instrument landing systems, comprising a first path adapted to receive a radio frequency carrier wave;

first power divider means for dividing the power of said carrier wave in said first path between a second path and a third path while maintaining isolation between said second path and said third path;

second power divider means for dividing the power of said carrier wave in said third path between a fourth path and a fifth path while maintaining isolation between said fourth path and said fifth path;

first constant input impedance sideband generator means modulating said carrier wave at a first audio frequency in said fourth path; and

second constant input impedance sideband generator means modulating said carrier wave at a second audio frequency in said fifth path, wherein said sideband generator means provide double sideband suppressed carrier signals and said modulator further comprises first means to combine the outputs of said sideband generator means and provide a difference output as a sideband only output of said modulator and a sum output in a sixth path and second means to combine said sum output with the carrier wave in said second path and provide a carrier wave output of said modulator.

3. A modulator as recited in claim 2, wherein one of said fourth and fifth path comprises variable attenuator means to control the relative amplitudes of said double sideband suppressed carrier signals and wherein one of said second path, third path, and sixth path comprises attenuator means to control the depth of modulation of said carrier wave output.

4. A modulator as recited in claim 3, further comprising attenuator means coupled to one of said outputs of said modulator to control the relative amplitudes of said outputs and phase shift means coupled to one of said outputs of said modulator to control the relative phase of said outputs.

5. A modulator as recited in claim 2, wherein each of said sideband generators comprises an impedance bridge network, means to vary impedances in said bridge network at a rate introducing an audio frequency modulation, means coupling the carrier wave from the corresponding one of said fourth and fifth paths to a first and a second side of said bridge network, and means introducing a phase reversal of said carrier wave in said second side of said bridge network with respect to said carrier wave in said first side of said bridge network.

6. A modulator as recited in claim 5, wherein said means introducing a phase reversal comprises a path from said corresponding path to an input terminal of said bridge network on said second side which is one-half wavelength longer than the path from said corresponding path to an input terminal of said bridge network on said first side.

7. A modulator as recited in claim 5, wherein said means introducing a phase reversal coMprises a transmission line in an arm of said bridge network on said second side which is a half wavelength longer than a transmission line in an arm of the bridge network on said first side.

8. A modulator as recited in claim 2, wherein each of said sideband generators comprises a capacitance bridge network and motor means modulating the capacitance of the capacitors of said bridge network at an audio frequency rate.

9. A modulator as recited in claim 8, wherein the capacitors of said capacitance bridge network comprise spaced, parallel stator plates having facing conductive patterns and said motor drives a rotor between said stator plates, said rotor having conductive patterns for varying the coupling between said facing conductive patterns of said stator plates at said audio frequency rate.

10. A modulator as recited in claim 9, wherein the shape and size of said conductive patterns on said stator plates, the shape and number of said conductive patterns on said rotor, and the speed of rotation of said rotor are so selected that a sinusoidal audio frequency modulation of the capacitance between said facing conductive patterns of said stator plates is effected.

11. Modulator means for an instrument landing system, comprising first power divider means for dividing a radiofrequency carrier wave into first and second portions;

second power divider means for dividing said second carrier wave portion into third and fourth portions;

separate sideband generator means including a pair of constant input impedance sideband generators means having respectively different operating frequencies for separately modulating said third and fourth carrier wave portions to produce first and second double sideband suppressed carrier signals of higher and lower frequency, respectively;

first combining circuit means for producing signals responsive to the sum and difference of said first and second double sideband suppressed carrier signals, respectively;

second combining circuit means for combining said first carrier wave portion with said sum signal of said first and second double sideband suppressed carrier signals to supply as a first output signal an amplitude modulated carrier wave signal; and

output circuit means connected with said first combining circuit means for supplying as a second output signal said difference signal of said first and second double sideband suppressed carrier signals.

12. Apparatua as defined in claim 11, and further including modulation balance control means comprising variable attenuator means connected with one of said sideband generator means for controlling the relative amplitudes of said double sideband suppressed carrier signals.

13. Apparatus as defined in claim 11, and further including means for controlling the depth of modulation of said first output signal, comprising variable attenuator means connected in at least one of the circuit paths between said first power divider means and said second combining circuit, said first combining circuit and said second combining circuit, and said first power divider means and said second power divider means, thereby controlling at least one of the inputs of said second combining circuit and said second power divider means.

14. A source of carrier wave, a first power divider having an input terminal connected to said source of carrier wave, said first power divider having two output paths, a second power divider responsive to signal in one of said two output paths, said second power divider having two further output paths, a first mechanically driven capacitive bridge sideband modulator connected in one of said further paths, a second mechanically driven capacitive bridge sideband modulator connected in the other of said further paths, said sideband modulators being arranged to modulate carrier signal in said paths at respectively different audio frequencies to produce suppressed carrier sideband signal energies, means for combining said sideband signal energies to form sum and difference siDeband signals in separate paths, hybrid combiner means for combining said sum sideband signals with carrier in one of said first mentioned output paths, and means for transmitting signal derived from said hybrid combiner in one path and said difference sideband signals in another path.

15. The combination according to claim 14, wherein said first and second power dividers are directional couplers having each a direct and a coupled path.

16. The combination according to claim 14, wherein is provided means for adjusting the relative amplitudes of said suppressed carrier sideband energies, and the relative amplitudes and phases of said carrier signal relative to said suppressed carrier sideband energies.

17. In an aircraft landing pattern transmitter, a source of unmodulated carrier wave, a first directional coupler connected directly in cascade with said source, said first directional coupler being arranged to divide the energy of said carrier wave into two first paths, a second directional coupler having an input port connected in one of said paths and having two second output ports, separate audio modulators connected directly in cascade with said two output ports, respectively, said modulators being adapted to have constant input impedances over a modulation cycle and to generate carrier suppressed double sideband signals, said modulators including only passive circuit elements.

18. The combination according to claim 17, wherein said modulators are motor driven balanced bridge modulators.

19. The combination according to claim 17, wherein said modulators are motor driven capacitor bridge modulators.

20. The combination according to claim 17, wherein is provided solely passive means for deriving the sum and the difference of said carrier suppressed double sideband signals in separate paths, solely passive means for combining said difference with the carrier wave in said other of said first paths to form a combined signal, means for transmitting said combined signal, and means for transmitting said sum signal.

21. The combination according to claim 36, wherein is provided solely passive means for deriving the sum and the difference of said carrier suppressed double sideband signals in separate paths, solely passive means for combining said difference with the carrier wave in said other of said first paths to form a combined signal, means for transmitting said combined signal, and means for transmitting said sum signal.

22. The combination according to claim 17, wherein all paths from said source of unmodulated carrier wave to said means for transmitting said combined signal and said means for transmitting said sum signal include only wholly passive circuit elements.

23. In an instrument landing system for aircraft, a source of carrier wave, means including only passive elements for dividing the power of said carrier wave into three separate paths which are mutually isolated from each other electrically, two passive element modulation systems connected respectively in first and second of said paths for forming carrier suppressed double sidebands of two discrete sideband frequencies, two circuit elements for combining said carrier suppressed double sidebands with said carrier respectively additively and subtractively.

24. The combination in accordance with claim 23, wherein the first recited means consists of two directional couplers connected in cascade.