Direction finding and frequency identification method and apparatus

• US 4,443,801 A
• Filed: 06/15/1981
• Issued: 04/17/1984
• Est. Priority Date: 06/15/1981
• Status: Expired due to Term

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Klose, Dirk R., Skudera William J. Jr.
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US06/273,806
• Time in Patent Office: 1,037 Days
• Field of Search: 343/113 R, 343/117 A, 343/119, 343/100 CL
• US Class Current: 342/442
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 3/74 Multi-channel systems specially adapted for direction-finding, i.e. having a single antenna system capable of giving simultaneous indications of the directions of different signals systems in which the directions of different signals are determined sequentially and displayed simultaneously G01S3/04, G01S3/14

Abstract

A surface acoustic wave interferometer direction finding and frequency idification method and apparatus is disclosed. The invention utilizes a plurality of dispersive delay lines in order to represent a multiplicity of signals, having different frequencies and angles of arrival at a plurality of antennae, by a train of pulses which retain phase information. Analysis of the interpulse spacing among the pulses in this pulse train, which represents the difference in frequency among the multiplicity of signals arriving at the antennae of the invention, and a pulse comparison of the signals at each of the antennas, allows selective correlation of signal with angle of arrival.

Claims

1. A method for determining the frequency and angle of a plurality of radio frequency signals of differing transmission frequency arriving essentially simultaneously at each of N spatially separated antennae of a radio frequency receiver, where N≧

2, comprising;

a first processing step wherein the received radio frequency signals arriving at each antenna are processed in such a manner as to obtain N composite signals, each representative of the plurality of radio frequency signals arriving at one of the antennae, all retaining the phase relationship of those radio frequency signals resulting from the spatial separation of the antennae, each having a frequency component representative of each of those radio frequency signals arriving at the antenna with which it is associated, and each being of suitable amplitude and frequency for further processing in a dispersive delay line;

introducing all of the N composite signals into dispersive delay lines, while retaining the phase relationship among those signals, so as to separate, in the time domain, components of each composite signal differing in frequency while retaining the phase relationship of those components representative of the spatial separation of the antennae;

a second processing step wherein the components of each of the composite signals are processed so as to determine the frequency of the radio frequency signal which they represent based on the position of each of the components in the time domain after their separation in the dispersive delay line while retaining the phase relationship of those components representative of the spatial separation of the antennae;

detecting the electrical phase relationship among components of the same frequency of different of the composite signals thereby determining electrical phase information about those signals;

converting the electrical phase information to angle of arrival information;

correlating the angle of arrival information for each component of each composite signal with the frequency information relative to that component; and

outputing the correlated information.

2. The method of claim 1 wherein said first processing step includes heterodyning the radio frequency signals to obtain intermediate frequency signals and further includes mixing these intermediate frequency signals with a frequency modulated sweeping signal.

3. The metod of claim 2 wherein said first processing step still further includes amplifying the mixed intermediate frequency signals prior to their introduction into the dispersive delay lines.

4. The method of claim 3 wherein said second processing step includes time gating the components of the composite signals so as to enable determination of the frequency of the radio frequency signals they represent.

5. The method of claim 3 wherein said second processing step further includes reducing the frequency of the components of the composite signal prior to their detection so as to enable the use of detectors operating in a lower frequency band.

6. A method for determining the frequency and angle of arrival of a plurality of radio frequency signals of differing transmission frequency arriving simultaneously at each of a pair of spatially separated antennae of a radio frequency receiver comprising:

processing the received signals arriving at each of the antennae so as to obtain two composite intermediate frequency signals, the first representative of the plurality of radio frequency signals arriving at one of the antennae and the second representative of the plurality of radio frequency signals arriving at the other antenna and both retaining the phase relationship of those radio frequency signals resulting from the spatial separation of the antennae and a frequency component representative of each of those radio frequency signals;

separately mixing and maintaining in individual channels the intermediate frequency signals representing the signals received at each antennae with a frequency modulated sweeping signal so as to further reduce the frequency and provide a plurality of frequency modulated sweeping signals representative of the plurality of the received signals at each antenna while retaining the phase relationship of the representative signals;

equally amplifying the resultant plurality of signals present in each channel while maintaining the phase relationship between them;

introducing the plurality signals in each channel into a dispersive delay line so as to separate signals of different frequency in the time domain so as to form a series of pulses in each channel while retaining the phase relationship between the corresponding signals in each channel;

amplifying the resultant signals to restore them for further processing while maintaining the phase relationship between the corresponding signals in each channel;

time gating and mixing the series of pulses in each channel so as to determine the transmission frequency each pulse represents and prepare the corresponding pulses in each channel for electrical phase detection;

detecting the electrical phase relationship of each pair of corresponding pulses in each channel;

computing the angle of arrival of the radio frequency signals at the antennae of the radio frequency receiver by utilizing the electrical phase relationship of each pair of radio frequency signals and the spatial separation of the antennae; and

correlating and displaying the angle of arrival and frequency of the received signals.

7. The method of claim 6 wherein phase ambiguities are eliminated by comparing the relative electrical phases of corresponding radio frequency signals as they are received at three or more antennae.

8. An apparatus for determining the frequency and angle of arrival of a plurality of radio frequency signals of differing transmission frequency arriving essentially simultaneously at each of N spatially separated antennae of a radio frequency receiver where N 2 comprising a first processing means wherein the received radio frequency signals arriving at each antenna are processed in such a manner as to obtain N composite signals, each representative of the plurality of radio frequency signals arriving at one of the antennae, all retaining the phase relationship of those radio frequency signals resulting from the spatial separation of the antennae, each having a frequency component representative of each of those radio frequency signals arriving at the antenna with which it is associated, and each being of suitable amplitude and frequency for further processing in a dispersive delay line;

dispersive delay means, electrically connected to said first processing means and operating so as to separate, in the time domain, components of each composite signal differing in frequency while retaining the phase relationship of those components representative of the spatial separation of the antennae;

a second processing means electrically coupled to said dispersive delay means, wherein the components of each of the composite signals are processed so as to determine the frequency of the radio frequency signal which they represent based on the position of each of the components in the time domain after their separation in the dispersive delay line while retaining the phase relationship of those components representative of the spatial separation of the antennae;

phase detection means, electrically coupled to said second processing means, for detecting the electrical phase relationship among components of like frequency of different of the composite signals thereby determining electrical phase information about those signals;

conversion means, electrically coupled to said phase detection means, for converting the electrical phases information to angle of arrival information;

correlating means, electrically coupled to said conversion means, for correlating the angle of arrival information for each component of each composite signal with the frequency information relative to that component; and

output means, electrically coupled to said correlating means for outputing the correlated information.

9. The apparatus of claim 8 wherein said first processing means includes means for heterodyning the radio frequency signals to obtain intermediate frequency signals and further includes means for mixing these intermediate frequency signals with a frequency modulated sweeping signal.

10. The apparatus of claim 9 wherein said first processing means still further includes means for amplifying the mixed intermediate frequency signals prior to their introduction into the dispersive delay lines.

11. The apparatus of claim 10 wherein said second processing means includes means for time gating the components of the composite signals so as to enable determination of the frequency of the radio frequency signals they represent.

12. The apparatus of claim 11 wherein said second processing means further includes means for reducing the frequency of the components of the composite signal prior to their detection so as to enable the use of detectors operating in a lower frequency band.

13. In an R.F. signal receiving system of the type having two antennas and a first and second independent processing channel each associated with one of the antennas, said processing channels having as their function as a minimum the detection of the R.F. signal received and the reduction of the range of frequency of the R.F. signal received to an intermediate frequency range while preserving the relative phase information of the signals received at each of said antennae, an improvement permitting the determination of both angle of arrival of one or a plurality of R.F. signals received at the antennae of the system and the transmission frequency of each of those R.F. signals comprising:

a first local oscillator means having an output terminal and producing a frequency modulated sweeping local oscillator signal at said output terminal;

a first coupling means having a first and second output terminal and an input terminal, electrically connected to the first local oscillator means for dividing the frequency modulated sweeping local oscillator signal into first and second substantially identical signals;

a first mixing means having a first and second input terminal and an output terminal and electrically connected at the first input terminal to the first output terminal of said first coupling means and electrically coupled at the second input terminal to the first processing channel of said receiving system, for mixing the first of the two substantially identical divided, frequency modulated, sweeping local oscillator signals with the intermediate frequency signal from the first processing channel of said receiving system;

a second mixing means having a first and second input terminal and an output terminal and electrically connected at the first input terminal to the second output terminal of said first coupling means and electrically coupled at the second input terminal to the second processing channel of said receiving system, for mixing the second of the two substantially identical divided, frequency modulated, sweeping local oscillator signals with the intermediate frequency signal from the second processing channel of said receiving system;

a first dispersive delay line having an input and output terminal, the input terminal of which is electrically connected to the output terminal of said first mixer means, for separating in the time domain, at its output terminal, signals of differing frequency introduced simultaneously at its input terminal;

a second dispersive delay line having an input and output terminal, the input terminal of which is electrically connected to the output terminal of said second mixer means, for separating in the time domain, at its output terminal, signal of differing frequency introduced simultaneously at its input terminal;

a second local oscillator means having an input and output terminal, electrically coupled to said first local oscillator means for signal synchronization purposes, having as its output a series of pulses for gating the outputs of said first and second dispersive delay lines;

a second coupler means, having one input and a first and second output terminal and having its input terminal electrically connected to the output of said second local oscillator means, for equally dividing the output signal from said second local oscillator means;

a third mixer means for mixing down and gating the signal from said first dispersive delay line, having a first and second input terminal and an output terminal, the first input terminal of which is electrically connected to the output terminal of said first dispersive delay line and the second input terminal of which is electrically connected to the first output terminal of said second coupler means;

a fourth mixing means for mixing down and gating the signal from said second dispersive delay line, having a first and second input terminal and an output terminal, the first input terminal of which is electrically connected to the output terminal of said second dispersive delay line and the second input terminal of which is electrically connected to the second output terminal of said second coupler means;

a third coupler means having one input and first and second output terminals for dividing the signal from said third mixer means and wherein said input terminal is electrically connected to the output terminal of said third mixer means;

a fourth coupler means having one input and first and second output terminals for dividing the signal from said fourth mixer means and wherein said input terminal is electrically connected to the output terminal of said fourth mixer and said second output is not utilized;

an electrical phase detector means for resolving into a first and second component the electrical phase difference of its input signals having first and second input terminals wherein said first input terminal is electrically connected to said first output terminal of said third coupler means and said second input terminal is electrically connected to said first output of said fourth coupler means, and further having first and second output terminals said first output terminal having a signal on it representative of the first component of the electrical phase difference of the signals from said third and fourth coupler means and said second output terminal having a signal on it representative of the second component of the electrical phase difference of the signals from said third and fourth coupler means;

calculator means, having a first and second input terminal and an output terminal, said first input terminal being electrically connected to the first output terminal of said electrical phase detector means and said second input terminal being electrically connected to said second output terminal of said electrical phase detector means, for calculating the angle of arrival of the received R.F. signal; and

a correlator and display means, having three input terminals and one output terminal, the first input terminal being electrically connected to the output terminal of said calculator means, the second input terminal being electrically connected to the second output terminal of said third coupler means, and the third input terminal being electrically responsive to said first local oscillator means for timing purposes, and providing a display of the correlation of angle of arrival and signal frequency at its output terminal.

14. The invention of claim 13 wherein amplifier means are introduced in series between the first mixing means and the first dispersive delay line, between the first dispersive delay line and the third mixing means, between the second mixing means and the second dispersive delay line and between the second dispersive delay line and the fourth mixing means in order to restore the signal for further processing.