Three-dimensional electromagnetic surveillance system and method

• US 4,701,762 A
• Filed: 10/17/1985
• Issued: 10/20/1987
• Est. Priority Date: 10/17/1985
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Sanders Associates, INC. (BAE Systems Plc)
• Inventors: Apostolos, John T.
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): Issing, Gregory C.
• Application Number:
  US06/788,291
• Time in Patent Office: 733 Days
• Field of Search: 343/417, 343/368, 343/451, 343/5 SA, 343/5 FT, 364/485, 364/726, 364/827, 342/417, 342/368, 342/451, 342/446, 342/195, 342/196, 342/192
• US Class Current: 342/417
• 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 surveillance system for simultaneously identifying the directions and frequencies of a plurality of electromagnetic-radiation sources includes an irregular array (10) of antenna elements and employs a two-dimensional compressive receiver (14) that receives at its input ports (18) the individual element signals. Each output of the two-dimensional compressive receiver (14) is modulated in an associated modulator (20) by one signal of a composite ensemble of signals. The composite ensemble is the sum of a plurality of individual ensembles, each of which is an ensemble of signals of a frequency uniquely associated with that individual ensemble and individually modulated to favor a direction associated with that individual ensemble. The results are added together in summation circuit 22 and applied to a Bragg cell (24), which segregates the results of modulation by the individual ensembles. When a pulse occurs at one of the output ports (28) of the Bragg cell (24), the time of occurrence of that pulse within the output sweep of the two-dimensional compressive receiver (14) indicates the temporal frequency of the antenna signal that gave rise to it, while the output port on which the pulse occurs is an indication of the direction of the source.

Claims

1. For use with an array of antenna elements that generate element signals in the presence of radio waves, a system for determining direction and frequency of the radio waves, comprising:

A. a Fourier-transformation device, including an input port associated with each antenna element and adapted for reception of the element signal therefrom, for performing a temporal Fourier transformation on the element signals to generate a plurality of transform signals in which the time at which a transform-signal component occurs indicates the temporal frequency of the element-signal component that gives rise to it;

B. a plurality of oscillators generating a like plurality of oscillator outputs, respectively;

C. means for storing modulation data to respectively modulate each transform signal, the modulation data, for each transform signal, being associated with each of a plurality of predetermined directions, each direction being associated with a respective oscillator and termporal frequency, the result of modulating each transform signal with the modulation data being to effect a coherent summation for each external source;

D. a modulator-translator circuit associated with each transform signal, each modulator-translator circuit being connected to receive the transform signal associated therewith and including;

i. a plurality of preliminary modulators, associated with respective ones of the oscillators and connected to receive the outputs of their associated oscillators, for fetching from the waveform-storage circuit the modulation data associated with the directions associated with the associated oscillators and with the temporal frequency of the element-signal components giving rise to the currently occurring transform-signal components, and for modulating the oscillator outputs in accordance with the fetched modulation data associated with the directions associated therewith to generate, for each of the directions, a preliminary-modulator signal associated with the associated transform signal;

ii. a preliminary summation circuit, connected to receive all of the preliminary-modulator signals generated from the associated transform signal, for adding them together to generate a preliminary summation signal associated with the associated transform signal; and

iii. a main modulator, connected to receive the associated transform signal and the preliminary summation signal associated therewith, for modulating the associated transform signal with the preliminary summation signal to generate a main-modulator signal associated with that transform signal;

E. a main summation circuit, connected to receive the main-modulator signals associated with all of the transform signals, for adding them together to produce a main summation signal; and

F. a frequency-segregation circuit connected to receive the main summation signal and generate therefrom a segregated output in which the segregated-output components generated from different oscillators are separated from each other to indicated the directions of the sources of the element signals that give rise to the segregated output.

2. A system as defined in claim 1 wherein the Fourier transformation device comprises a device for generating the transform signals by performing a two-dimensional temporal-spatial Fourier transformation on the element signals.

3. A system as defined in claim 2 wherein the device for performing the two-dimensional Fourier transformation comprises a two-dimensional compressive-receiver.

4. A method for determining the functions of phase shift and attenuation versus azimuth, elevation angle, and temporal frequency for use with an array of antenna elements that generate element signals, together with a Fourier-transformation device having an input port associated with and operably connected to each antenna element for performing a temporal Fourier-transformation on the antenna element signals, the Fourier-transformation device also having a plurality of output ports, comprising the steps of:

A. for each of a plurality of discrete combinations of azimuth, elevation angle, and temporal frequency, causing a source to radiate at a given temporal frequency and azimuth and elevation angle;

B. adjusting the phase shift and attenuation at a plurality of output ports of the compressive receiver until a maximum value is reached in the sum of the compressive-receiver output ports, thereby obtaining a phase shift value and an attenuation value; and

C. storing in a data storage device the phase shift value and attenuation value associated with each discrete combination of azimuth, elevation angle and temporal frequency.