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Compensation of direction finding estimates for polarimetric errors
| Details |
Inventors: Owens, Mark A.;
Assignee: Raytheon Company (Lexington, MA)
Primary Examiner: Gregory; Bernarr E.
Assistant Examiner:
Attorney, Agent or Firm: Collins; David W., Lenzen, Jr.; Glenn H.
An algorithmic technique which allows antenna arrays that are used for interferometric direction finding to have elements with arbitrary orientation. This technique allows the phase errors associated with non-identical element orientation to be estimated, without explicit knowledge of either the polarimetrics of the array elements or the polarimetrics of the source. It relies upon the fact that there exists a single number which describes the polarimetric interaction, and that this number can be estimated and then utilized to remove the phase component due to polarimetric interaction. This technique makes it feasible to incorporate direction finding arrays into articles that could benefit from such arrays, but because of size or shape constraints, were previously not able to do so. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Consider the simple case of a two element interferometer, where each element is aligned with the baseline, and with a source lying directly ahead of the two elements on a line normal to the baseline.
In this case, the electrical phase at each element would be equal, and the measured direction of arrival (solid angle from baseline) would be 90 degrees.
Now let one of the two elements be rotated by a known angle of .
alpha.
degrees with respect to the other first element, as shown in FIG.
1A.
Here, the baseline axis is denoted as "x," and the array 10 includes elements 12 and 14, with element 14 rotated by angle .
alpha.
with respect to the axis x and the orientation of the element 12.
The output ports 12A and 14A of the elements 12 and 14 are connected to respective mixer circuits 16A and 16B for mixing with a local oscillator (LO) signal to downconvert the signals received at the array elements, and then amplified by respective amplifiers 18A, 18B to provide respective complex voltages V.
sub.
1 and V.
sub.
2.
These output voltages are provided to a receiver/processor 20, which computes the estimated angle of arrival of the signal from the source, in accordance with the invention.
FIG.
1B illustrates an exemplary detection technique for detecting the received signals, in this example only at array element 12A.
The signal from the array element 12A is amplified by an RF amplifier 13A before downconversion to IF by the LO mixer 16A.
The downconverted signal is then detected by a quadrature detector 15A which outputs two voltages, i.
e.
the in-phase (I) and the quadrature (Q) voltages.
The I and Q voltages provide two channels which are digitized by analog-to-digital convertors 17A and 19A.
The digitized I and Q signals form a pair of number (I, Q) that can be treated as one complex number, i.
e.
z=I+jQ.
The processor 20A can be a general purpose embedded processor, a digital signal processor, or a PC for a rack mounted system.
It will be appreciated that similar two channel quadrature detectors will be employed for each array element forming the detection system 10
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Radio 
