Bae Systems Information and Electronic Systems Integration Inc.

Callahan Cellular LLC

Keith A Struckman

Robert T Martel

Richard E Clymer

Allan M Kabel

Gideon Litoff

Gerald J Pellegrini

A method for improving direction finding and geolocation error estimation in direction finding and geolocation systems is disclosed. The corresponding phases of the received signals are determined. After an initial target estimation point of the received signals has been identified, the initial target estimation point is projected onto the earth's surface. A search grid having multiple grid points is then overlaid on the projected initial target estimation point, surrounding the projected initial target estimation point. The phase of signals emitting from a theoretical emitter located at each of the grid points of the search grid is estimated. Correlation coefficients between the estimated phases of the emitting signals and the determined phases of the received signals are determined. An error ellipse can be generated around one of the grid points having the highest correlation coefficient, and a source emitter is likely to be located within the error ellipse.

Method for improving direction finding and geolocation error estimation in a direction finding system

A concentric ring, log-periodic slot antenna used for direction finding is disclosed. There are a number of continuous, circular slots nested inside of each other. A cover over the slots cavities has excitation plates and conductors thereon. There are four excitation plates spaced ninety degrees apart over each circular slot, and the excitation plates of all slots in each ninety degree sector are electrically interconnected. A conductor from the interconnected excitation plates in each of the four sectors conducts received signals to a Butler matrix which processes the signals and provides Mode 0, Mode +1, Mode &#x2212;1, and Mode &#x394; outputs. These Mode outputs are used to provide direction finding information for DF signal sorting, and they may be used to provide radio frequency voltages to other equipment to provide accurate DF (CIDF) and CIGL transmitter geo-location information.

Concentric ring log-periodic slot direction finding antenna

A method is disclosed for processing all types of received, interfering radio frequency signals corrupted by noise to extract the individual signals without having any a priori knowledge about them. Received signals are converted for eigenspace processing and are subjected to repeated non-linear time domain and fast Fourier transform frequency domain processing that calculates eigenstream beam forming weights U. By performing calculations in eigenspace, the number of independent weights U that must be calculated is generally reduced, minimizing calculating time. Once the weights U have been calculated in eigenspace they are transformed into antenna beam forming weights W that are used to extract the individual signals and to determine the angle of arrival of each of the individual signals. Further time is saved because the weights W do not have to be updated for every time slice of the received signals.

Method for separating interfering signals and computing arrival angles

A radio geolocation system is described in which a plurality of moving platforms such as aircraft concurrently receive a signal from a remote transmitter and the geolocation of the transmitter is determined. At each platform every thirty seconds a plurality of samples of the received signal are taken over a one second period. The samples are digitized and a time and GPS location stamp are added to each sample. The digitized samples with time and location stamps from all platforms are transmitted to a central location and stored in covariance matrices, one matrix per one second sample period. The signal samples in each matrix are processed utilizing a unique algorithm to generate a data set which defines a correlation surface. The data from a plurality of data sets are summed together on a point by point basis and normalized to yield a summation data set which defines a summation correlation surface. The summation correlation surface has a well defined peak that defines the geolocation of the remote transmitter.

Multiplatform TDOA correlation interferometer geolocation

Apparatus and a method utilizing correlation interferometer direction finding for determining the azimuth and elevation to an aircraft at long range and flying at low altitudes above water with a transmitting radar while resolving multipath signals. The signals from the radar are received both directly and reflected from the surface of the water using horizontally polarized and vertically polarized antenna arrays, are digitized and are stored in separate covariant matrices. Eigenvalues for the eigenvectors of the matrices processed on signal samples recorded on horizontally polarized X arrays are compared to the eigenvalues for the eigenvectors of the covariance matrices processed on signal samples recorded on vertically polarized X arrays. Incident field polarization is associated with the antenna array measurements that yield the strongest eigenvalue. The eigenvector and eigenvalues for the strongest signal are selected and used for subsequent signal processing. An initial global search assuming mirror sea-state reflection conditions using the signal eigenvector having the strongest eigenvalue is performed to yield an approximate elevation &#x3b1; and azimuth &#x3b2; to the aircraft. The approximate values are then used as the starting point for a subsequent conjugate gradient search to determine accurate elevation &#x3b1; and azimuth &#x3b2; to the aircraft.

Multipath resolving correlation interferometer direction finding

A Moving Transmitter Correlation Interferometer Geo-Location (MT-CIGL) system is disclosed that permits locating both moving and stationary transmitters from moving DF equipment. A conjugate gradient based search routine is utilized which solves for the location of moving and stationary transmitters at the start of each measurement sequence and then solves for the velocity and direction of motion of the moving transmitter. This information is used to track the moving transmitter. Received signals are sampled, digitized and stored in covariance matrices. They are then summed and normalized using an equation that has velocity terms that are set to zero to minimize extraneous correlation peaks, and a maximum correlation peak is developed. A conjugate gradient search routine is used to find the correlation peak of the summed data. The value of the peak is then analyzed to see if it is above or below a predetermined value. If the peak value is above the predetermined value the transmitter is stationary and the located correlation peak is the location of the transmitter. If the peak value is below the predetermined value the transmitter is moving and the peak does not indicate the correct location of the transmitter. Another conjugate gradient search routine is performed using the previous erroneous peak as the starting point for the search to identify the actual location of the moving transmitter at the beginning of a search sequence. That location is then processed through the same equation, but without the velocity terms set to zero, to calculate the velocity and direction of motion of the transmitter. This information can then be used to plot a track for the moving transmitter.

Moving transmitter correlation interferometer geolocation

Correlation Interferometer Geo Location (CIGL) uses DF antenna array movement on an aircraft while taking a Plurality of sets of transmitted signal Measurements. Each measurement set is stored as data in a covariance matrix, and the matrices are each decomposed to yield measured array vectors. Using an array manifold table developed during calibration of the CIGI. system, and containing testing array vectors, the measured array vectors are each correlated to testing array vectors to develop a correlation Surface that includes compensation for perturbations Such as aircraft induced electromagnetic scattering, All the correlation surfaces are summed and normalized, with the resultant summation undergoing conjugate gradient processing to more accurately geo-locate the transmitter. Improved accuracy with fewer antennas and polarization independence are also achieved.

Correlation interferometer geolocation

A technique is disclosed for calculating the phase and amplitude weighting factors for use with a specific compact antenna range that synthesize an in phase, constant amplitude planar wave front that appears to have been transmitted from the far field. The weighting factors are used to weight RF signals after they are received by a full size or scaled radio direction finding array mounted on a platform during testing of the antenna array on the compact antenna range. The weighted received signals accurately replicate the antenna array response in the far field, including electromagnetic glint caused by the platform on which the antennas are mounted, and are stored in complex voltage form as a calibration table for the array.

Near field to far field DF antenna array calibration technique

A microwave imaging excavator for the detection, imaging and excavation of objects on or buried beneath the surface of the ground, such as metallic and dielectric land mines. A continuous wave stepped frequency ground penetrating radar signal is transmitted into the ground from a waveguide antenna mounted in one spade of a double spade auger. Direct breakthrough energy, signals reflected from the surface and the buried objects are received by an identical waveguide antenna mounted in the opposite spade. The spectra reflected from different buried objects become more distinct when the spectrum radiated spans the natural electromagnetic resonance of those objects. These signals are recorded as the twin-spaded auger is mechanically scanned over the ground in two mechanical rotational states of polarization. When the auger spades are on either side of a buried mine they are closed to grasp the mine which is then removed from the ground.

Growing community of inventors

Grand Junction, CO, United States of America

Keith A Struckman