U.S. patent application number 10/345776 was filed with the patent office on 2004-07-15 for enhanced emitter location using adaptive combination of time shared interferometer elements.
Invention is credited to Krikorian, Kapriel V., Rosen, Robert A..
Application Number | 20040135724 10/345776 |
Document ID | / |
Family ID | 32594869 |
Filed Date | 2004-07-15 |
United States Patent
Application |
20040135724 |
Kind Code |
A1 |
Krikorian, Kapriel V. ; et
al. |
July 15, 2004 |
ENHANCED EMITTER LOCATION USING ADAPTIVE COMBINATION OF TIME SHARED
INTERFEROMETER ELEMENTS
Abstract
An interferometer array system and method for processing pulse
signals from a target emitter includes an n element interferometer
array of radiator elements for producing radiator signals in
response to the pulse signals from the target emitter. M processing
channels process radiator signal elements, where m<n. A switch
matrix is connected between the array and the processing channels,
switching different combinations of the radiator elements to the
channels within a single pulse to achieve processing of all
radiator signals within a single pulse of said pulse signals from
the target emitter.
Inventors: |
Krikorian, Kapriel V.; (Oak
Park, CA) ; Rosen, Robert A.; (Simi Valley,
CA) |
Correspondence
Address: |
PATENT DOCKET ADMINISTRATION
RAYTHEON SYSTEMS COMPANY
P.O. BOX 902 (E1/E150)
BLDG E1 M S E150
EL SEGUNDO
CA
90245-0902
US
|
Family ID: |
32594869 |
Appl. No.: |
10/345776 |
Filed: |
January 15, 2003 |
Current U.S.
Class: |
342/424 ;
342/437 |
Current CPC
Class: |
G01S 3/48 20130101 |
Class at
Publication: |
342/424 ;
342/437 |
International
Class: |
G01S 005/02 |
Claims
What is claimed is:
1. An interferometer array system for estimating a location of a
target emitter, comprising: an n element interferometer array of
radiator elements for producing radiator element signals in
response to signals from the target emitter; m processing channels
for processing radiator element signals, where m<n; a switch
matrix connected between the array and the m processing channels,
the switch matrix for switching different combinations of said
radiator elements to said channels within a single pulse; angle
estimation means responsive to the m processing channels for
estimating emitter angles; an adaptive switch selector for
adaptively selecting subsets of interferometer array elements to
improve emitter location accuracy.
2. The system of claim 1, wherein the angle estimation means
comprises: processing means for extrapolating phase information;
maximum likelihood angle estimation means for providing a maximum
likelihood estimate of the target emitter location in response to
the phase information.
3. The system of claim 2, wherein the angle estimation means
provides one or more likely target location estimates, and the
adaptive switch selector is responsive to the maximum likelihood
estimate of the target emitter location and the one or more likely
target location estimates, and adaptively determines said subsets
of radiator elements to be adaptively selected for processing
during a subsequent pulse.
4. The system of claim 1, wherein the switch matrix is responsive
to control signals from the adaptive switch selection processor to
select said subsets of radiator elements during a pulse.
5. A method for estimating location of an emitter using an
interferometer array of n radiator elements with m processing
channels, comprising: passing signals from the n radiator elements
through a switch matrix to the m processing channels, where m<n;
during a single pulse, switching different combinations of radiator
elements to respective ones of the m processing channels;
processing the outputs from the m processing channels for the
single pulse to develop likely angle locations of the emitter.
6. The method of claim 5, wherein the different combinations of
radiator elements constitute non-overlapping groups of
elements.
7. The method of claim 6, further comprising: determining the
relative phases between the radiator element signals.
8. The method of claim 6, wherein said determining the relative
phases comprises: performing coherent processing over time by first
frequency channelizing each element, estimating the frequency of
detected emitters, and extrapolating the phase to a common
time.
9. The method of claim 5, wherein the different combinations of
radiator elements constitute overlapping groups of elements.
10. The method of claim 9, further comprising: determining the
relative phases between the radiator element signals.
11. The method of claim 10, wherein said determining the relative
phases comprises: determining relative phases between respective
elements in different groups by adding or subtracting the relative
phases of the respective elements with the phase of a common
element.
Description
BACKGROUND OF THE DISCLOSURE
[0001] Interferometer arrays are used to provide accurate
localization of emitters. Most systems support a limited number of
simultaneous interferometer channels over several antenna elements
resulting in ghosting and degraded localization particularly in
dense emitter environments. Current implementations also depend on
the accurate de-interleaving of pulse trains from different
emitters.
[0002] Prior attempts depended on de-interleaving pulse trains and
could coherently combine only a limited number of interferometer
elements resulting in significantly larger error rates and poorer
precision.
SUMMARY OF THE DISCLOSURE
[0003] An interferometer array system for processing pulse signals
from a target emitter includes an n element interferometer array of
radiator elements for producing radiator signals in response to the
pulse signals from the target emitter. M processing channels
process radiator signal elements, where m<n. A switch matrix is
connected between the array and the processing channels, switching
different combinations of the radiator elements to the channels
within a single pulse to achieve processing of all radiator signals
within a single pulse of said pulse signals from the target
emitter.
BRIEF DESCRIPTION OF THE DRAWING
[0004] These and other features and advantages of the present
invention will become more apparent from the following detailed
description of an exemplary embodiment thereof, as illustrated in
the accompanying drawings, in which:
[0005] FIG. 1 is a schematic system block diagram of an embodiment
of an interferometer array in accordance with aspects of the
invention, employing an array of time-shared radiator elements.
[0006] FIG. 2 is a processing block diagram further illustrative of
the system of FIG. 1.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0007] For an interferometer, coherent (complex voltage)
measurements from each element are used to determine the relative
phases and derive the angles of arrival of the emitter. For reduced
costs the number of simultaneous emitter channels can be reduced.
This reduction in the number of simultaneous receive channels can
cause angle ambiguities. A technique is described to overcome this
deficiency.
[0008] Fast intra-pulse switching reduces ghosting from multiple
emitters and achieves accurate two-dimensional (2-D) angle of
arrival on a single pulse basis. Coherent combination can be
employed to achieve the enhanced performance of large
interferometer arrays with a limited number of simultaneous
channels.
[0009] Fast intra-pulse switching among interferometer elements is
provided by currently available switches. Using an adaptive element
switching strategy and coherent combination of elements, very
precise localization of emitters is achieved within a short time
without the de-interleaving of pulse trains.
[0010] An exemplary embodiment of an n element interferometer array
system 50 is illustrated in the schematic system block diagram of
FIG. 1 and the processing block diagram of FIG. 2. As can be seen
in FIG. 1 the system has n radiator elements 52, and m processing
channels 56, where m<n. The system includes a switching matrix
54 between the elements 52 and the processing channels 56. The
switching matrix 54 may restrict the combinations of elements that
can be processed simultaneously. Known switch technology is capable
of achieving switching in less than half a microsecond, which is
significantly shorter than the pulse width of most emitters. A
simple implementation of the switch matrix may include m single
pole double throw switches, with each switch connecting one channel
to two elements. This embodiment of the invention exploits the fast
switching capability to process the contributions of the radiator
elements of the interferometer within a single pulse. This allows
estimation of emitter locations without the need of de-interleaving
emitter pulse trains.
[0011] In an exemplary embodiment, each channel includes an RF
filter, e.g. filter 56A-1, for filtering the radiator signal, a
frequency down-converter, e.g. mixer 56B-1, for mixing the filtered
RF signal with a local oscillator (LO) signal, an I/Q detector,
e.g. detector 56D-1, and an analog-to-digital converter (ADC), e.g.
ADC 56E-1. The digitized signals from each channel is fed to signal
processor 100. Functions performed by an exemplary signal processor
100 are shown in FIG. 2.
[0012] In the simplest application, the elements 52 are grouped in
non-overlapping sets without utilizing the relative phase between
the groups. Improved performance can be achieved by determining the
phase between all the elements.
[0013] In another application, overlapping groups of elements 52
are employed. The relative phase between any two elements in
different groups can be determined by appropriately adding or
subtracting the relative phases with a common element.
[0014] Alternatively, for non-overlapping groups of elements 52,
coherent processing may be performed over time by first frequency
channelizing each element using frequency channelizers 58 (FIG. 2),
i.e., an FFT over the collected time samples, estimating the
frequency of detected emitters using an emitter detector function
60 and frequency centroid and phase estimation function 62, and
extrapolating the phase to a common time by phase extrapolator
function 64. The extrapolated phase is obtained by adding the
estimated phase increment to the measured phase. The estimated
phase increment is given by
.DELTA..PHI.=2.pi.f.sub.est.DELTA.t
[0015] where
[0016] f.sub.est=estimated emitter frequency from the frequent
centroid
[0017] .DELTA.t=time increment to the next processing interval
[0018] The measured phase is given by:
.PHI..sub.meas=atan2(Q,I)
[0019] where I and Q are the real and imaginary parts of the FFT
filter output, atan2(Q, I) is the notation for the arctangent of
the ratio of Q to 1, and the arctangent may be obtained by table
lookup. The frequency estimates are improved by combining the
measurements from all the channels. For wideband coded pulses,
estimates from several FFT filters from each element will be used
to determine the relative phase. The relative phases are then
combined using a maximum likelihood estimator 68 to obtain accurate
emitter locations with low gross error rate. An adaptive switch
function 70 is employed to change the switch selection.
[0020] An exemplary efficient implementation of the maximum
likelihood estimator 68 is a 2-D FFT using the element phasors and
locations. In addition, beside the maximum likelihood estimate, the
other likely locations are also output. Based on these locations, a
best subset of interferometer array elements can be adaptively
selected using the adaptive switch selection function 70. A new set
of measurements is then taken to further improve the emitter
location accuracy and reduce the gross error rate. For example, for
an n=8 element interferometer with m=4 receive channels and channel
i connected to elements 2i and 2i-1 (where i=1, . . . , 4), an
element configuration of 1, 4, 5 and 8 could be commanded based on
earlier measurement made with elements 2, 3, 6 and 8.
[0021] It is understood that the above-described embodiments are
merely illustrative of the possible specific embodiments which may
represent principles of the present invention. Other arrangements
may readily be devised in accordance with these principles by those
skilled in the art without departing from the scope and spirit of
the invention.
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