Patent ID: 6791493
Filing Date: 2004-09-14
Classification: G01S

Abstract:
A method of passively determining agile-frequency-emitter location, comprising the steps of:measuring during a single receiver dwell: phase at a minimum of three different carrier frequencies on a single interferometer baseline; wherein: each frequency measurement occurs with a phase measurement; and each corresponding interferometer baseline position, the position simultaneous to the phase and frequency measurements; processing the measurements measured by the measuring step by: multiplying each baseline by the corresponding frequency; forming a linearly independent set of differences of these baseline-frequency products; and forming the corresponding set of phase differences; determining the measuring step has obtained sufficient phase, frequency and baseline measurements, comprising: based on the linearly independent set of differences of baseline-frequency products produced by the processing step, predicting the accuracy of a direction of arrival unit vector or COS(AOA) to be that will be computed from the corresponding set of phase differences; repeating the measuring step and processing step until the predicted accuracy meets or exceeds a desired specified accuracy; computing an array A of gains based on the set of baseline-frequency product differences, where there is a gain for each difference, and the sum of the differences weighed by each corresponding gain is a null vector; computing the phase difference ambiguity integers for all the phase difference measurements by: processing the phase difference measurements corresponding to the set of baseline-frequency products by: multiplying each phase difference with the corresponding gain, where the gain was previously determined; and summing these products to form a fundamental test metric; forming all possible sequences of permissible ambiguity integers, such that each sequence is an array having the same dimensions as the set of phase differences; testing each integer set thus formed by: weighting each integer in the set with the corresponding gain determined in the computing an array step; summing these weighted values; and choosing the sum closest to the fundamental test metric; and resolving the set of phase differences with the set of integers whose sum has the value closest to that of the fundamental test metric by adding the integer array to the phase array; estimating the emitter DOA unit vector {right arrow over (u)} or COS(AOA) by: computing a second array &Lgr; of gains from the set of baseline-frequency product differences, where the matrix product of the gains and differences is the identity matrix; determining the rank of the set of baseline-frequency product differences; estimating {right arrow over (u)} if the rank is greater than 1, and COS(AOA) otherwise, by forming the matrix product of &Lgr; with the phase differences corresponding to the baseline-frequency differences; predicting the LBI phase differences, the differences occurring between receiver dwells, by: if the rank of the set of baseline-frequency product differences is greater than 1, performing the steps of: projecting the DOA unit vector found in each dwell on a single baseline measured in that dwell; and scaling the projected value by the measured frequency corresponding to the baseline measurement; else if the rank of the set of baseline-frequency product differences is 1, performing the steps of: forming the product of the COS(AOA) and baseline length; scaling the product by the measured frequency corresponding to the measured phase being resolved; resolving the corresponding ambiguous measured phase difference by: differencing the ambiguous phase difference with the predicted phase difference and estimating the resulting integer value; adding the integer value to the ambiguous phase; and associating the resolved phase change with spatial angle change and estimating emitter range from the angle change.