Radio frequency arraying method for receivers

• US 4,186,347 A
• Filed: 10/31/1978
• Issued: 01/29/1980
• Est. Priority Date: 10/31/1978
• Status: Expired due to Term

• Current Assignee: Frosch Robert A Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, Mahlon F. Easterling, Milton H. Brockman
• Original Assignee: Frosch Robert A Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, Mahlon F. Easterling, Milton H. Brockman
• Inventors: Brockman, Milton H., Frosch, Robert A. Administrator of the National Aeronautics and Space Administration, with respect to an invention of, Easterling, Mahlon F.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Gerasimow, Alexander
• Application Number:
  US05/956,160
• Time in Patent Office: 455 Days
• Field of Search: 325/305, 325/307, 325/419-421, 325/56, 325/60, 325/167, 325/171
• US Class Current: 375/344
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity

Abstract

A method and apparatus for increasing the signal-to-noise ratio of a receiving facility for coherent frequency reception by arraying receiving systems using separate antennas for each, or one antenna for all systems. One system is operated with a carrier tracking loop to provide a first local oscillator frequency for the first and all other systems arrayed, with individual tracking loops in all other systems operated at IF for tracking out any phase differences due to separate group delays using an adjustable phase shifter for a second reference (REF. 2) to compensate for different group delays in the antenna and low-noise amplifier of each of the other systems. The second IF output of all systems are summed into the first system. This technique may also be used when two systems are arrayed to an antenna designed for circular or linear polarization diversity reception to effectively provide the same signal-to-noise ratio for both polarized signal transmission channels that would result from matched polarization. An arrangement adapted to high rate telemetry reception is disclosed. With additional components, the same arrangement is adapted to provide low rate telemetry reception as well.

Claims

1. A method for arraying a plurality of receiving systems coupled to one or more antennas for coherent frequency reception, each receiving system having a first IF mixer and a second IF mixer, comprising the steps of

carrier frequency tracking in one receiving system utilizing a phase-lock loop to control the frequency of a first local oscillator for the first IF mixer thereof, and using the output of said first local oscillator as the local oscillator for the first IF mixer of each of the remaining systems,

carrier phase tracking in each of said remaining receiving systems relative to said one receiving system at IF frequency using a constant reference frequency for the second IF mixer in said one receiving system, and in each remaining system using a phase-lock loop to control the frequency of a second local oscillator for the second IF mixer thereof, and

summing of the second IF signals in all of said remaining receiving systems with the second IF signal in said one receiving system.

2. A method as defined in claim 1 including making a separate and fixed phase shift adjustment in the carrier phase tracking loop of each remaining receiving system to cancel differential RF carrier phase due to any group delay in its antenna coupling.

3. A method as defined in claim 1 wherein said receiving systems are two in number coupled to one antenna, a first receiving system for right circular or vertical linear polarization and a second receiving system for left circular or horizontal linear polarization diversity reception, thereby to effectively provide the same signal-to-noise ratio for both polarizations that would result from matched polarization.

4. A method as defined in claim 1 for high rate telemetry reception including the steps of setting the signal level of the summed second IF signals in the one receiving system to provide the required level for the telemetry subcarrier spectrum of the one receiving system with respect to the other systems, adjusting the closed loop noise bandwidth of the remaining receiving systems to compensate for low carrier signal-to-noise ratio relative to the one receiving system and including a distribution amplifier in each receiving system to feed the output of the second IF mixer to the tracking loops of each respective receiving system and in at least one system to a separate telemetry subcarrier channel of broad bandwidth.

5. A method as defined in claim 4 for low or high rate telemetry reception including maintaining the low threshold of the array utilizing a filter operating at a fixed narrow-band noise bandwidth in each of said remaining receiving systems for reducing the phase noise in the summing of the second IF signals in all of said remaining receiving systems with the second IF signal in said one receiving system.

6. A method as defined in claim 5 wherein said filter is comprised of an additional second IF mixer in each of said remaining receiving systems and a narrow-band local oscillator tracking loop feeding the second local oscillator signal to said additional second mixer, and summing the output of said second mixer in each of said remaining receiving system with the output of the second mixer of said one receiving system.

7. A method for increasing the sensitivity of a receiving facility for coherent radio frequency reception by arraying a plurality of receiving systems which receive a modulated carrier signal from the same or separate antennas, operating one of the arrayed systems as a master with a carrier tracking loop to provide to a first heterodyne mixer in each of said plurality of receiving systems a first local oscillator frequency used to produce a first IF signal in each system, operating each of said plurality of systems except the first with individual tracking loops at the first IF to provide a second local oscillator frequency to a second heterodyne mixer for producing a second IF signal in each system while the master receiving system is operated with a first fixed reference signal to be mixed with the first IF to produce the second IF, and using a separate adjustable phase shifter for adjustment of the second local oscillator frequency in each of the other systems arrayed to compensate for differences in group delay of the received signal through the receiving antenna and preamplifier coupling into the first mixer, thereby to provide second IF signals that are in phase, and summing the second IF signals of all systems with the second IF signal of the first system.

8. A method as defined in claim 7 wherein said receiving facility is for polarization diversity reception from a single antenna with its associated feed, and only two systems are arrayed, one for polarized reception of one sense or angle, and a second one for polarized reception of another sense or angle, and wherein a selected one of the two systems is operated as the master with a carrier tracking loop, and the other with a tracking loop operating at said first IF.

9. A method as defined in claim 7 for high rate telemetry reception including the step of setting the signal level of the summed IF signals in the master system to provide the required level for the telemetry subcarrier spectrum of the master receiving system with respect to the other systems arrayed, narrowing the closed loop bandwidth of the other systems to compensate for low carrier signal-to-noise ratio relative to the master system, and including a distribution amplifier to feed the second IF signal to the tracking loops of each respective receiving system and to a separate telemetry subcarrier channel of broad bandwidth in each receiving system.

10. A method as defined in claim 9 for low or high rate telemetry reception including maintaining the low threshold of the arrayed receiver systems, and including a local oscillator tracking loop operating at a fixed bandwidth of 0.01 of the threshold noise bandwidth of the master in each of the other receiving systems for reducing the phase noise at the summing junction, thereby preserving the master receiving system threshold as the combined receiving system threshold, said local oscillator tracking loop being effected through a seocnd mixer into the distribution amplifier, while the IF signal produced by the phase tracking loop of the receiver system is passed through a matching group delay amplifier.

11. A radio frequency receiving facility moving a plurality of receiving systems coupled to one or more antennas for coherent frequency reception, each receiving system having a first IF mixer and a second IF mixer, comprising:

means for carrier frequency tracking in one receiving system utilizing a phase-lock loop to control the frequency of a first local oscillator for the first IF mixer thereof,

means for using the output of said first local oscillator as the local oscillator for the first IF mixer of each of the remaining systems,

means for carrier phase tracking in each of said remaining receiving systems relative to said one receiving system at IF frequency using a constant reference frequency for the second IF mixer in said one receiving system, and in each remaining system using a phase-lock loop to control the frequency of a second local oscillator for the second IF mixer thereof, and

means for summing of the second IF signals in all of said remaining receiving systems with the second IF signal in said one receiving system.

12. A radio frequency receiving facility as defined in claim 11 including means for making a separate and fixed phase shift adjustment in the carrier phase tracking loop of each remaining receiving system to cancal differential RF carrier phase due to group delay in its antenna coupling.

13. A radio frequency receiving facility as defined in claim 11 wherein said receiving systems are two in number coupled to one antenna, a first receiving system for right circular or vertical linear polarization and a second receiving system for left circular or horizontal linear polarization diversity reception, thereby to effectively provide the same signal-to-noise ratio for both polarizations that would result from matched polarization.

14. A radio frequency receiving facility as defined in claim 11 for high rate telemetry reception including

means for setting the signal level of the summed second IF signals in the one receiving system to provide the required level for the telemetry subcarrier spectrum of the first receiving system with respect to the other systems,

means for adjusting the closed loop noise bandwidth of the remaining receiving systems to compensate for low carrier signal-to-noise ratio relative to the one receiving system, and

a distribution amplifier in each receiving system to feed the output of the second IF mixer to the tracking loops of each respective receiving system and to a separate telemetry subcarrier channel of broad bandwidth in each receiving system.

15. A radio frequency receiving facility as defined in claim 14 for low or high rate telemetry reception including means for maintaining the low threshold of the array utilizing a filter operating at a fixed narrow-band noise bandwidth in each of said remaining receiving systems for reducing the phase noise in the summing of the second IF signals in all of said remaining receiving systems with the second IF signal in said one receiving system.

16. A radio frequency receiving facility as defined in claim 15 wherein said filter is comprised of an additional second IF mixer in each of said remaining receiving systems and a narrow band local oscillator tracking loop feeding the second local oscillator signal to said additional second mixer, and means for summing the output of said second mixer in each of said remaining receiving system with the output of the second mixer of said one receiving system.

17. In a facility for coherent radio frequency reception, a plurality of receiving systems which receive a modulated carrier signal from the same or separate antennas, apparatus for combining said receiving systems to increase the sensitivity of said facility for coherent radio frequency reception, comprising

a carrier frequency tracking loop in one of said receiving systems to provide to a first heterodyne mixer in each of said plurality of receiving systems a first local oscillator frequency used to produce a first IF signal in each receiving systems,

a separate carrier phase tracking loop in each of said one to provide a second local oscillator frequency signal to a second heterodyne mixer for producing a second IF signal in each receiving system in phase with a second IF signal in said one receiving system produced in a second heterodyne mixer thereof by beating with a fixed reference frequency signal,

means for separately adjusting the phase of said second local oscillator frequency in each of said receiving systems except said one system to compensate for difference in group delay of the received signal relative to the group delay of the received signal in said one receiving system, and

means for summing the second IF signals of all of said receiving systems with the second IF signal in said one receiving system.

18. Apparatus as defined in claim 17 wherein said receiving facility is for polarization diversity reception from a single antenna with its associated feed, and only two systems are arrayed, one for polarized reception of one sense or angle, and a second one for polarized reception of another sense or angle, and wherein a selected one of the two systems is operated as the one with a carrier frequency tracking loop, and the other with a carrier phase tracking loop operating at said first IF.

19. Apparatus as defined in claim 17 for high rate telemetry reception including

means for setting the signal level of the summed IF signals in the one receiving system to provide the required level for the telemetry subcarrier spectrum of said one receiving system with respect to the other receiving systems arrayed,

means for narrowing the closed loop bandwidth of the other systems to compensate for low carrier signal-to-noise ratio relative to the master system, and

a distribution amplifier to feed the second IF signal to the tracking loops of each respective receiving system and to a separate telemetry subcarrier channel of broad bandwidth in each receiving system.

20. A apparatus as defined in claim 19 for low or high rate telemetry reception including means for maintaining the low threshold of the arrayed receiver systems, and including a local oscillator tracking loop operating at a fixed bandwidth of 0.01 of the threshold noise bandwidth of said one receiving system in each of the other receiving systems for reducing the phase noise at the summing means, thereby preserving threshold of one receiving system as the combined receiving system threshold, said local oscillator tracking loop being effected through a second mixer into said distribution amplifier, while the IF signal produced by the phase tracking loop of the receiver system is passed through a matching group delay amplifier.