Ambiguity resolving algorithm for interferometers of arbitray topologies

• US 5,742,252 A
• Filed: 08/26/1996
• Issued: 04/21/1998
• Est. Priority Date: 08/26/1996
• Status: Expired due to Term

• Current Assignee: Raytheon Company (Rtx Corporation)
• Original Assignee: Raytheon Company (Rtx Corporation)
• Inventors: Bui, Loan Taree, Nguyen, Trung T.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US08/703,310
• Time in Patent Office: 603 Days
• Field of Search: 342/156, 342/424, 342/147
• US Class Current: 342/156
• CPC Class Codes: G01S 3/46 using antennas spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems

Abstract

An apparatus for reducing the computational requirements for resolving ambiguity in interferometer measurements where the interferometer elements are arranged arbitrarily. Each of a plurality of interferometer elements each measures the phase of the incoming electromagnetic signal. The interferometer elements are each separated by lengths defined as baselines, which are sorted and processed in ascending order. Following initialization, for each baseline (92, 108), the phase measurements of the next baseline (92, 108) to be processed are estimated. If the measured phases (94-100, 110-118) of the next baseline (92, 108) falls within a predetermined range (104, 106) of the estimated phases, the phase is retained for estimating the phases of the next baseline. After a sufficient number of baselines have been processed, the angle of the incoming electromagnetic signal may be determined in accordance with the retained phases.

Claims

1. A system for determining an angle of incidence for an incoming electromagnetic signal, the system comprising:

a plurality of interferometers for detecting the incoming electromagnetic signal, each interferometer measuring a phase based upon the incoming electromagnetic signal in accordance with the position of the interferometer relative the incoming electromagnetic energy, where each interferometer is separated by a distance defined as a linear baseline between the two; and

a signal processor for computing the angle of the electromagnetic signal in accordance with the phases measured by the interferometers, the processor performing the steps of;

(a) determining an initial phase estimate in accordance with two selected baselines in order to predict a phase measured for another of the plurality of baselines,

(b) for the other baselines, predicting a phase for a next baseline in accordance with the phases measured for a previously selected baseline and measuring the phase of the next baseline to determine if the measured phase is within a predetermined range of the predicted phase, and

(c) determining the angle of the incoming electromagnetic signal in accordance with the phases of the last baseline falling within the predetermined ranges of the predicted phases;

wherein the phase measurements φ

_i for an ith baseline may be defined as follows;

##EQU7## d_xⁱ,d_yⁱ are the x and y components, respectively, of baseline i;

n_i is the phase noise with zero mean and variance σ

_n² ;

Az and El are the azimuth and elevation, respectively, defined with respect to the normal of the antenna plane; and

λ

is the wavelength of the incoming electromagnetic signal.

2. The system of claim 1 wherein the estimated phase φ

_k/k is defined as follows;

##EQU8## where φ

_k/k is the phase estimate at baseline k for a given k value.

3. The system of claim 2 wherein an ordered pair exists as defined below:

##EQU9##

4. The system of claim 3 wherein the predicted phase φ

_k+1/k has a variance Var (φ

_k+1/k) defined in accordance with ##EQU10##

5. The system of claim 4 wherein the predetermined range gate k+1 is defined as ##EQU11## where nsigma is the number of desired standard deviations.