Space diversity receiving system with phase-controlled signal combining at intermediate frequency stage

• US 4,079,318 A
• Filed: 06/22/1976
• Issued: 03/14/1978
• Est. Priority Date: 06/23/1975
• Status: Expired due to Term

• Current Assignee: Nippon Electric Company Limited (NEC Corporation)
• Original Assignee: Nippon Electric Company Limited (NEC Corporation)
• Inventors: Kinoshita, Kyo
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Bookbinder, Marc E.
• Application Number:
  US05/698,639
• Time in Patent Office: 630 Days
• Field of Search: 325/56, 325/301, 325/303-306, 325/366, 325/367, 325/369, 325/476, 343/205
• US Class Current: 455/139
• CPC Class Codes: H04B 7/084 Equal gain combining, only phase adjustments antenna beam scanning or forming by phase or amplitude control H01Q3/26, e.g. phased arrays

Abstract

A space diversity receiving system is described which eliminates the low frequency phase modulation component at the intermediate frequency stage output. Received signals from two antennae are converted to intermediate frequency signals and then combined after one signal has been passed through a variable phase shifter. Branching amplifiers are provided in each intermediate frequency channel so that all phase modulation, phase detection and production of the control signal necessary for controlling the variable phase shifter are achieved outside of all main intermediate frequency channels that are to be combined to obtain an intermediate frequency output.

Claims

1. A diversity receiving system of the type wherein a plurality of received signals are combined in an in-phase relationship at an intermediate frequency, comprising:

(a) at least first and second channels, each of said first and second channels including a first frequency conversion means for converting a respective one of said received signals to an intermediate frequency signal and branching means connected to receive the signal from said first frequency conversion means for providing first and second output signals, said first channel further including phase variation means connected between said first frequency conversion means and said branching means for altering the phase of the output intermediate frequency signal from said first frequency conversion means,

(b) first combining means connected to receive the first output signals of the branching means in each of said at least first and second channels for providing a first combined output signal, and

(c) phase variation control means for controlling said phase variation means in said first channel, said phase variation control means including phase detection means connected to receive the second output signals of the branching means in each of said at least first and second channels for detecting the phase difference between said second output signals, and control signal generator means connected to said phase detection means and responsive to the output of the phase detection means for generating a control signal to said phase variation means to cause the signals at the inputs of said first combining means to be in-phase, wherein said phase detection means comprises;

(i) a phase modulator connected to receive the second output signal from the branching means in either of said at least first and second channels,

(ii) second combining means for combining the remaining second output signals from the branching means in said at least first and second channels with the output of said phase modulator,

(iii) a phase detector for providing an output signal to said control signal generator means, said phase detector being connected to receive the output of said second combining means, and

(iv) an oscillator connected to provide oscillation frequency signals to said phase modulator to modulate its input signal and to said phase detector as a reference frequency to detect the modulating signal in the output of said second combining means.

2. A space diversity receiving system according to claim 1, wherein said second channel further includes delay equalizer means connected to receive the first output signal from said branching means for compensating for the delay time caused by said phase variation means in said first channel.

3. A space diversity receiving system according to claim 1, further comprising at least first and second automatic gain control amplifiers connected to receive the second output signals from the branching means in each of said at least first and second channels, respectively, for maintaining said second output signals at a constant amplitude.

4. A space diversity receiving system of the type wherein a plurality of received signals are combined in an in-phase relationship at an intermediate frequency, comprising:

(a) at least first and second channels, each of said first and second channels including a first frequency conversion means for converting a respective one of said received signals to an intermediate frequency signal and branching means connected to receive the signal from said first frequency conversion means for providing first and second output signals, said first channel further including phase variation means connected between said first frequency conversion means and said branching means for altering the phase of the output intermediate frequency signal from said first frequency conversion means,

(b) first combining means connected to receive the first output signals of the branching means in each of said at least first and second channels for providing a first combined output signal, and

(c) phase variation control means for controlling said phase variation means in said first channel, said phase variation control means including phase detection means connected to receive the second output signals of the branching means in each of said at least first and second channels for detecting the phase difference between said second output signals, and control signal generator means connected to said phase detection means and responsive to the output of the phase detection means for generating a control signal to said phase variation means to cause the signals at the inputs of said first combining means to be in-phase, wherein said phase variation means in said first channel includes;

(i) a second frequency conversion means for converting the first intermediate frequency signal output from said first frequency conversion means to a second intermediate frequency signal,

(ii) first oscillator means for providing a plurality of first oscillation frequency signals,

(iii) a variable phase shifter connected to receive a first oscillation frequency signal from said first oscillator means, said variable phase shifter receiving a control signal from said control signal generator means and providing a frequency conversion signal to said second frequency conversion means, and

(iv) third frequency conversion means, connected to receive the first output signal from said branching means, for converting a second intermediate frequency signal to said first intermediate frequency signal, said third frequency conversion means receiving, as a frequency conversion signal, a first oscillation frequency signal from said first oscillator means.

5. A space diversity receiving system according to claim 4, wherein said phase detection means comprises:

(a) fourth frequency conversion means connected to receive the second output signal from the branching means in said first channel, for converting said second output signal to said first intermediate frequency signal,

(b) a phase modulator for supplying a frequency conversion signal to said fourth frequency conversion means, said phase modulator receiving, as its input signal, a first oscillation frequency signal from said first oscillator means,

(c) second combining means connected to receive the output of said fourth frequency conversion means and the second output signal from the branching means in said second channel,

(d) a phase detector for providing an output signal to said control signal generator means, said phase detector being connected to receive the output signal from said second combining means, and

(e) second oscillator means for providing second oscillation frequency signals to said phase modulator to modulate said first oscillation frequency signal and to said phase detector as a reference frequency to detect the modulating signal in the output of said second combining means.

6. A space diversity receiving system according to claim 5, further comprising first and second automatic gain control amplifiers for maintaining the respective inputs to said second combining means at a constant amplitude.

7. A space diversity receiving system according to claim 4, wherein said second channel further includes delay equalizer means connected to receive the first output signal from said branching means for compensating for the delay time caused by said phase variation means in said first channel.

8. A space diversity receiving system of the type wherein a plurality of received signals are combined in an in-phase relationship at an intermediate frequency, comprising:

(a) at least first and second channels, each of said first and second channels including a first frequency conversion means for converting a respective one of said received signals to an intermediate frequency signal and branching means connected to receive the signal from said first frequency conversion means for providing first and second output signals, said first channel further including phase variation means connected between said first frequency conversion means and said branching means for altering the phase of the output intermediate frequency signal from said first frequency conversion means,

(b) first combining means connected to receive the first output signals of the branching means in each of said at least first and second channels for providing a first combined output signal, and

(c) phase variation control means for controlling said phase variation means in said first channel, said phase variation control means including phase detection means connected to receive the second output signals of the branching means in each of said at least first and second channels for detecting the phase difference between said second output signals, and control signal generator means connected to said phase detection means and responsive to the output of the phase detection means for generating a control signal to said phase variation means to cause the signals at the inputs of said first combining means to be in-phase, wherein said phase variation means includes a variable phase shifter comprising;

(i) second branching means for branching the input to said variable phase shifter into first and second input signals,

(ii) first and second phase shifter channels for receiving said first and second input signals, respectively, each of said first and second channels containing a 3-terminal circulator connected to receive a respective input signal at the first terminal thereof, and providing a respective output signal at the third terminal thereof, said second channel further containing a 90°

fixed phase shifter for phase shifting the input to said 3-terminal circulator,

(iii) and second combining means for providing a variable phase shifter output, connected to receive the output signals from each of said circulator means, and

(iv) control signal converter circuits connected to the second terminal of each said 3-terminal circulator, the impedance of said control signal converter circuits being varied in response to signals received from said control signal generator means.

9. A space diversity receiving system according to claim 8, wherein said control signal generator means comprises:

(a) a comparator connected to receive a signal from said phase detection means, said comparator having a variable-polarity direct current signal output, the polarity of said output being dependent upon the signal received from said phase detection means,

(b) a gate circuit,

(c) a clock pulse generator for providing clocking pulses to said gate circuit, said gate circuit emitting output pulses corresponding to each said clocking pulse having a polarity dependent on the polarity of the output of said comparator at the time of each corresponding clocking pulse,

(d) reversible counting means for counting the output pulses from said gate circuit, the direction of counting being dependent on the polarity of said output pulses, the output of said reversible counting means being a saw tooth wave signal having an amplitude dependent upon the total count accumulated by said reversible counting means during each respective period of said saw tooth wave signal,

(e) third branching means for branching out first and second counting signals, connected to receive the output from said reversible counting means, and

(f) first and second wave shifting means for converting said first and second counting signals, respective, into triangular wave control signals, said control signals being 90°

out-of-phase with respect to each other and applied to said control signal converter circuits of said variable phase shifter.