United States of America As Represented by the Secretary of the Air Force

Other

James B Tsui

Rudy L Shaw

Richard B Sanderson

David L Sharpin

James N Hedge

William S McCormick

David M Lin

John J Schamus

Joseph Caschera

Nicholas A Pequignot

David C Tsui

Robert L Davis

Lihyeh Liou

David B Choate

David H Kaneshiro

Gerd H Schrick

A new approach for applying the multiple signal classification (MUSIC) method for high spectral resolution signal detection is described. The new approach uses a lower order covariance matrix, or, alternately, an autocorrelation matrix, to calculate only the number of eigenvalues and associated eigenvectors actually needed to solve for the number of signals sought.

Low order multiple signal classification (MUSIC) method for high spectral resolution signal detection

A method for determining distance from a target to an observation station using a Global Positioning System satellite as a radiation source and first and second observation station located receivers. The first receiver receives reflected position determinative satellite radio frequency signals and the second receiver receives direct position determinative satellite radio frequency signals. The time difference between satellite radio frequency signals arriving at the first and second receivers is calculated and combined with difference distance data and angular, azimuth and elevational position data and the distance from the target to observation point is determined.

Passive ranging using global positioning system

A broadband gigahertz frequency range radio receiver useful in electronic warfare and other applications for incoming signal detection and identification purposes. The receiver is based on Fourier transform examination of incoming signal characteristics and provides real time accomplishment of these tasks by way of using a simplified one-bit digital representation of the incoming signals and a resulting reduction of the computational load associated with the Fourier transform operation. The receiver precedes the Fourier transform operation with signal processing which may include, for example, a limiting amplifier and two bandpass filters. Two incoming signal accommodation is provided, a characteristic which is particularly improved over the characteristics of popular presently used receivers in this field.

Monobit kernel function electronic warefare receiver for characterizing

The present invention provides a realization of a real-time, high frequency Fourier transformation using a single binary-bit kernel function which reduces the mathematical operation mechanizations needed to generate a Fourier transformation from multiplication and associated dense, complex hardware to simple addition and subtraction associated hardware components. The single binary-bit kernel function Fourier transformation generated produces a constant peak amplitude regardless of the number of bits in the input data and is most useful for applications where input data is composed of 1 and 2 binary bits.

Fourier transform mechanization using one bit kernel function

Two signal monobit electronic warfare receiver

An instantaneous frequency measurement receiver (IFM) is used at each output of a digital channelized receiver. A Fast Frequency Transform (FFT) is used to form an instantaneous frequency measurement (IFM) receiver at every frequency component. These IFM receivers can perform frequency coding and produce fine frequency measurement.

Digital channelized IFM receiver

This system compares the phases from Fast Frequency Transform (FFT) outputs to obtain angle of arrival (AOA) information.

AOA application of digital channelized IFM receiver

Disclosed is a method to extract the periodic properties (or Pulse Repetition Intervals (PRIs)) of radar signals whose time-of-arrival at an airborne platform have been time tagged by an Electronic Warfare (EW) receiver. The PRIs are determined using a modified Discrete Fourier Transform (DFT) written as ##EQU1## where k represents the frequency components, the T.sub.i are the individual Time-Of-Arrival (TOA) data values and N is the last TOA value collected. Disclosed are three possible methods of reducing the number of computations involved with the modification of the Discrete Fourier Transform (DFT) equation to facilitate its use with Radar Time-Of-Arrival (TOA) to extract periodic properties of radar signals. This is particularly applicable to radar pulse trains which are interleaved in time and where each individual pulse train may be staggered or jittered in time so that a time domain deinterleaving scheme must be employed. A spectral estimator can be computed by taking the modulus of the DFT of the time series data and extending the periodogram estimator by making a slight modification of the DFT equation.

Spectral estimation of radar time-of-arrival periodicities

The technique to measure the frequency very accurately for electronic warfare (EW) applications, and is simple in hardware, and which can accomplish this goal with a signal with real data (in contrast to complex data). It uses trigonometric identities to compute the location of the zero, which is very precise, but requires the use of an inverse trigonometric function. From these crossings, one can find the frequency very accurately using only one channel of data. The input signal is down converted and digitized with one A/D converter. The digitized data is used to find the zero crossing. The resolution of the zero crossing is limited by the clock cycle. Three uniformly digitized points around a zero crossing are used to find the time for the crossing. The device according to the invention will calculate the frequency very accurately using only one channel of data. This method can be used to measure the angle of arrival in a two antenna configuration with very precise results where the distance between the two antennas does not exceed half the wavelength of the incoming signal.

Highly accurate zero crossings for frequency determination

This invention is directed to an expendable which includes an electronic circuit for introducing a simulated Doppler frequency shift. When dropped from an aircraft, the expendable is used to confuse hostile radar operations. In the past, the approach has been to use a high frequency electronic switch (PIN diode) and drive oscillator to change the impedance of the expendable antenna. This invention involves a simplification which combines the electronic switch and its drive oscillator into a single semiconductor component. By connecting a feedback circuit from the collector to the base of a high frequency transistor as well as to the two arms of the antenna, the antenna impedance is changed at the transistor oscillating frequency.

Self-mixing expendable

The circuit may be used to encode the channel outputs of a Bragg cell receiver, or other type of channelized receiver. Bragg cell receivers use acousto-optic delay lines to analyze signals such as radar pulses present in the Electronic Warfare (EW) environment. These receivers require high probability of intercept with low false alarm rates. The present design in determining frequency from a Bragg receiver is by comparing the amplitude from adjacent outputs. If the output of a certain channel is higher than its neighboring ones and the signal crosses threshold, the frequency of the input signal is determined by that channel. There is one major deficiency from this approach, that is, the design generates false alarms. A frequency encoding circuit is proposed which uses five adjacent channels to make a decision on whether a given output is a true signal, or a false alarm. With this approach, two guard channels will be needed at both ends of the channels.

Frequency encoding circuit in Bragg cell receiver

This is an arrangement to find two folding frequencies that fold into one frequency bin, which will save hardware. The input frequency in down converted into I and Q channels. Each channel requires one pair (two) of A/D converters. A total of three pairs of A/D converters are required. All three pairs of A/D converters have the SAME sampling frequency f.sub.s. There is a time delay of .tau. before the second pair of A/D converters, and 2.tau. before the third pair. At the outputs of the A/D converters FFT units followed by a signal processor are used to find the input frequencies by solving non-linear simultaneous equations.

Frequency measurement receiver with means to resolve two folding

The technique allows precise angle-of-arrival (AOA) and radio frequency measurements on non-cooperative radar signals, by exploiting precise phase measurement capabilities of frequency measurement receivers. It is assumed that the intercept receivers with this capability are on board an aircraft and there are at least two antennas available. By utilizing the phase measurements, the incident frequency and incident phase angle are calculated using formulae derived under the disclosed technique. By taking multiple samples and averaging, angle measurement errors can be reduced.

Doppler frequency angle measurement technique

In multiple frequency estimation, the bandwidth and resolution of Fast Fourier Transform (FFT) based frequency estimators are limited by A/D converter sampling rate constraints and also by real-time computational requirements. The disclosed configuration uses a Modified Chinese Remainder Theorem of a paper entitled, 'A Noise Insensitive Solution to an Ambiguity Problem in Spectra Estimation' by McCormick et al and a subsampling approach of U.S. Pat. No. 5,099,194 entitled, 'Digital Frequency Measurement Receiver With Bandwidth Improvement Through Multiple Sampling of Real Signals' to resolve the frequency ambiguity problem. The configuration extends these ideas to the multiple frequency case. It significantly extends system bandwidth by operating I FFT units in parallel at specific sampling rates chosen to maximize system bandwidth for a fixed level of noise protection. Each FFT unit output is processed by a 'peak detecting' algorithm that detects the M remainders of the M frequencies for the sampling frequency, F.sub.i, of that particular FFT unit. Using a multiple frequency ambiguity resolution algorithm, the M frequencies are estimated from the I sets of M remainders. The configuration essentially resolves the 2.pi. or aliasing ambiguity problem for multiple frequencies in a parallel, highly efficient manner. In its current configuration, the system is designed for complex signal inputs.

Frequency measurement receiver with means to resolve an ambiguity in

An IFM (Instantaneous Frequency Measurement) receiver is disclosed that can process two simultaneous signals for electronic warfare application. Three IFM receivers are employed (cooperating in the 2 to 4 GHZ range) and have three filters in front of them. Filter 1 is a 2-4 GHz band pass receiver in front of the first receiver. In front of the second receiver is a low pass filter with a band edge at 2 GHz. In front of the third receiver is a high pass filter with the band edge at 4 GHz. In filters 2 and 3, the skirts of the filters are used rather than their pass bands. Details on the signal conditions, calculations for the frequencies, and the equations are disclosed.

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Dayton, OH, United States of America

James B Tsui