Complex Fourier coefficient extractor
AssigneeThe United States of America as represented by the Secretary of the Navy
InventorsEdward Alexander, Anthony Spezio, Hal Levitt, Brian Krantz
Life of this patent
Estimating the term…
Abstract
A system for extracting the complex Fourier coefficients from an unknown RF signal to classify the RF signal is disclosed. The extraction system utilizes optical signal processing in combination with the generation of electronic timing and control signals. The system employs an optical processor comprising a Bragg cell to yield the Fourier coefficients including the amplitude, phase and frequency parameters thereof. The system further includes a parallel arrangement that provide for parallel processing to reduce the computational time needed to determine the complex Fourier coefficients including the amplitude, phase and frequency parameters thereof.
Claims11
An apparatus for extracting complex Fourier coefficients from an RF signal of interest so as to characterize said RF signal, said RF signal having a leading edge and modulation, said extracting apparatus comprising:
- (a) receiving means for receiving said RF signal and generating first and second timing signals in response to said leading edge of said RF signal, said receiving means downconverting and demodulating said RF signal to a baseband so as to remove a carrier frequency but leaving a modulation voltage, said downconverted, demodulated RF signal serving as an output of said receiving means;
- (b) means for generating a signal of interest and a reference signal for a two acoustic column Bragg cell device, said signal of interest and reference signal generating means receiving said downconverted, demodulated RF signal and said first timing signal, said signal of interest and reference signal generating means including a local oscillator;
- (c) an optical processor comprising said Bragg cell, a laser, a Fourier lens, and an array of spatially positioned means each responsive to intercepted optical signals to correspondingly produce n electrical signals that represent a pattern of said intercepted optical signals, said Bragg cell having first and second acoustic columns respectively connected to said signal of interest and reference signal of said signal of interest and reference signal generating means;
- and
- (d) means for receiving said pattern of said intercepted optical signals and extracting therefrom said complex Fourier coefficients.
An apparatus for extracting complex Fourier coefficients from an RF signal of interest so as to characterize said RF signal, said RF signal having a leading edge and modulation, said extracting apparatus comprising:
- (a) receiving means for receiving said RF signal and generating first and second timing signals in response to said leading edge of said RF signal, said receiving means downconverting and demodulating said RF signal to a baseband so as to remove a carrier frequency but leaving a modulation voltage, said downconverted, demodulated RF signal serving as an output of said receiving means;
- (b) means for generating a signal of interest and a reference signal for a two acoustic column Bragg cell device, said signal of interest and reference signal generating means receiving said downconverted, demodulated RF signal and said first timing signal;
- (c) an optical processor comprising said Bragg cell, a laser, a Fourier lens, and an array of spatially positioned means each responsive to intercepted optical signals to correspondingly produce n electrical signals that represent a pattern of said intercepted optical signals, said Bragg cell having first and second acoustic columns respectively connected to said signal of interest and reference signal of said signal of interest and reference signal generating means;
- and
- (d) means for receiving said pattern of said intercepted optical signals and extracting therefrom said complex Fourier coefficients;
- wherein said means for generating said signal of interest and said reference signal comprises first, second and third branches which, in turn, respectively comprise:
- (i) said first branch comprising means for receiving said downconverted, demodulated RF signal, means for delaying said received downconverted, demodulated RF signal by a predetermined amount, a mixer having first and second inputs and an output with the first input receiving said delayed downconverted, demodulated RF signal and with said output providing said signal of interest of said Bragg cell device;
- (ii) said second branch comprising an oscillator with an output and pseudorandom noise (PRN) generator with an output, said oscillator and said pseudorandom noise (PRN) generator both being activated in response to said first timing signal and with said output of said oscillator being applied to said pseudorandom noise (PRN) generator which is responsive thereto, said second branch further comprising a mixer having first and second inputs and an output with the first input receiving said output of said pseudorandom noise (PRN) generator and said output of said mixer providing said reference signal of said Bragg cell device;
- and
- (iii) said third branch comprising a local oscillator having first and second outputs with said first output connected to said second input of said mixer of said first branch and said second output connected to said second input of said mixer of said second branch.
Dependencies are inferred from the claim text.