Leo Hochi Hui

US Patent:

6750809, Jun 15, 2004

Filed:

Apr 15, 2003

Appl. No.:

10/414322

Inventors:

Kwang M. Cho - Rancho Palos Verdes CA
Leo H. Hui - Alhambra CA

Assignee:

Raytheon Company - Waltham MA

International Classification:

G01S 1338

US Classification:

342129, 342201, 342204, 342132

Abstract:

A radar system has improved range resolution from linear frequency modulated (LFM) first sub-pulse and second sub-pulse, both having linear frequency modulation about different center frequencies. The first transmitted sub-pulse and the second transmitted sub-pulse have chirp slope. Sample shifting and phase adjusting is performed for the first radar returns with respect to second radar returns to form a line of frequency modulated chirp slope with respect to time, the line connecting the center frequencies of the center frequencies. The first sub-pulse and second-sub pulse can have equal time duration, where the first and second center frequency are equidistant from a reference frequency. The returns are reflected by a target located at a location near a reference point s. The radar computes the reference frequency f centered with respect to the first center frequency f and the second center frequency f , a reference time a time delay to said reference point s with respect to time t for m= a time delay to said reference point s with respect to said reference time t , where The first sub-pulse returns received from the first sub-pulse are shifted by an amount Typically, the radar de-chirps returns prior to sample shifting and phase adjusting.

US Patent:

6965341, Nov 15, 2005

Filed:

Dec 15, 2003

Appl. No.:

10/734956

Inventors:

Kwang Myung Cho - Rancho Palos Verdes CA, US
Leo H. Hui - Alhambra CA, US

Assignee:

The United States of America as represented by the Secretary of the Air Force - Washington DC

International Classification:

G01S013/90
G01S013/38

US Classification:

342 25A, 342 25 R, 342 25 F, 342128, 342129, 342130, 342131, 342132, 342175, 342195, 342200, 342201, 342202, 342205

Abstract:

A stepped-frequency chirped waveform improves SAR groundmapping for the following reasons. Range resolution in SAR image is inversely proportional to the transmitted signal bandwidth in nominal SAR systems. Since there is a limit in the transmitted bandwidth that can be supported by the radar hardware, there is a limit in range resolution that can be achieved by processing SAR data in conventional manner. However, if the frequency band of the transmitted signal is skipped within a group of sub-pulses and received signal is properly combined, the composite signal has effectively increased bandwidth and hence improvement in range resolution can be achieved. The proposed new and practical approach can effectively extend the limit in range resolution beyond the level that is set by the radar hardware units when conventional method is used.

US Patent:

7006031, Feb 28, 2006

Filed:

Oct 19, 2004

Appl. No.:

10/968780

Inventors:

Theagenis J. Abatzoglou - Huntington Beach CA, US
Leo H. Hui - Alhambra CA, US
Kwang M. Cho - Rancho Palos Verdes CA, US

Assignee:

Raytheon Company - Waltham MA

International Classification:

G01S 13/90

US Classification:

342 25A, 342195, 342159, 342 25 F, 342 25 D, 342196

Abstract:

SAR images are improved by a method for acquiring a synthetic aperture image from a sequence of periodic pulse returns where the sequence of periodic pulse returns is interspersed with interrupts, i. e. missing pulses. The interrupts mark the start and end of one or more segments, where the segments contain the periodic pulse returns form the SAR image. The method comprises the steps of:The computation for extrapolating the missing pulse returns is introduced after the Stolt interpolator in RMA processing. In computing the model order, eigenvalues are found and compared to a threshold. Roots of a linear prediction polynomial are computed, then stabilized to obtain stabilized roots. Linear prediction coefficients are reconstituted using the stabilized roots. Sub-bands are used to decrease computing time for the missing pulse returns.

US Patent:

7145496, Dec 5, 2006

Filed:

Nov 23, 2004

Appl. No.:

10/996246

Inventors:

Kwang M. Cho - Rancho Palos Verdes CA, US
Leo H. Hui - Alhambra CA, US

Assignee:

Raytheon Company - Waltham MA

International Classification:

G01S 13/90

US Classification:

342 25R, 342 25 D, 342 25 F, 342161, 342196

Abstract:

A radar on a moving platform generates an initial synthetic aperture (SAR) image of a scene from a sequence of periodic pulse returns approximately motion compensated. The SAR image is formed from pixel intensities z(x,y) within a x,y extent of the initial synthetic aperture image. Targets are selected from the initial synthetic aperture image using a sliding window, computing a first entropy for the selected targets, and sorting the targets using the first entropy to obtain a target list having target elements, then concatenating the target elements to form a data matrix compatible in the azimuth dimension with a Fast Fourier Transform. A phase correction for autofocus is iteratively computed and applied to the initial synthetic aperture image using an inner loop, a mid loop and an outer loop. The phase correction is expressed using an orthogonal polynomial having a plurality n consecutive terms a, adenoting a quadratic term, and adenoting a last order term. The outer loop, using an L index, calculates an outer loop E(a) entropy for the quadratic term and an outer loop E(a) entropy for the last order term.

US Patent:

7145498, Dec 5, 2006

Filed:

Aug 10, 2005

Appl. No.:

11/200836

Inventors:

Kwang M. Cho - Los Angeles CA, US
Leo H. Hui - Alhambra CA, US

Assignee:

Raytheon Company - Waltham MA

International Classification:

G01S 13/90

US Classification:

342 25R, 342 25 F, 342 25 D, 342161, 342162, 342196

Abstract:

A moving radar generates a search mode synthetic aperture image of a patch from periodic pulse returns reflected from the patch. The patch is imaged from radar returns derived from two or more overlapping arrays. A strong scatterer is located within each array, then the data from each array is motion compensated with respect to the motion of the radar and the strong scatterer. The motion compensated results for each array are autofocused to derive a phase error for each array. Using the phase error for each array, a connected phase error estimate is computed, added to the phase error of each array to minimize the differences between phases in the overlap between arrays insuring that there is no or minimal phase discontinuity in the overlap region between arrays. Avoiding phase discontinuity yields a clear SAR image of the combination of arrays rendering the patch.

US Patent:

7277042, Oct 2, 2007

Filed:

May 12, 2006

Appl. No.:

11/433707

Inventors:

Kwang M. Cho - Los Angeles CA, US
Leo H. Hui - Alhambra CA, US

Assignee:

Raytheon Company - Waltham MA

International Classification:

G01S 13/90
G01S 13/00

US Classification:

342 25F, 342 25 R, 342 25 A, 342 25 D, 342165, 342173, 342174, 342175, 342195, 342196

Abstract:

A radar acquires a formed SAR image of radar scatterers in an area around a central reference point (CRP). Target(s) are within the area illuminated by the radar. The area covers terrain having a plurality of elevations. The radar is on a moving platform, where the moving platform is moving along an actual path. The actual path is displaced from an ideal SAR image acquisition path. The radar has a computer that divides the digital returns descriptive of the formed SAR image into multiple blocks, such as a first strip and an adjacent strip. The first strip is conveniently chosen, likely to generally align with a part of the area, at a first elevation. An adjacent strip covers a second part of the area at a second elevation. The first strip is overlapping the adjacent strip over an overlap portion. The first and second elevation are extracted from a terrain elevation database (DTED).

US Patent:

7301495, Nov 27, 2007

Filed:

Jan 11, 2006

Appl. No.:

11/329764

Inventors:

Theagenis John Abatzoglou - Huntington Beach CA, US
Leo H. Hui - Alhambra CA, US
Kwang M. Cho - Los Angeles CA, US

Assignee:

Raytheon Company - Waltham MA

International Classification:

G01S 13/90
G01S 13/89
G01S 13/00

US Classification:

342 25F, 342 25 R, 342 25 A, 342 89, 342 90, 342175, 342176, 342179, 342192, 342195, 342196

Abstract:

A moving radar () generates a synthetic aperture image from an incomplete sequence of periodic pulse returns. The incomplete sequence of periodic pulse returns has one or more missing pulses. The radar converts the incomplete sequence of pulse returns into a digital stream. A computer () processes the digital stream by computing an along track Fourier transform (), a range compression (), an azimuth deskew () and an image restoration and auto focus (). The image restoration and autofocus () utilizes a low order autofocus (), a gap interpolation using a Burg algorithm (), and a high order autofocus () for generating an interpolated sequence. The interpolated sequence contains a complete sequence of periodic pulse returns with uniform spacing for generating the synthetic aperture image. The image restoration and autofocus () computes a linear prediction coefficients estimate using the Burg Algorithm (). The linear prediction coefficients estimate () is used to compute a weighted forward-backward interpolation to generate the complete sequence of periodic pulse returns ().

US Patent:

7532150, May 12, 2009

Filed:

Mar 20, 2008

Appl. No.:

12/077669

Inventors:

Theagenis J. Abatzoglou - Huntington Beach CA, US
Leo H. Hui - Alhambra CA, US

Assignee:

Raytheon Company - Waltham MA

International Classification:

G01S 13/90

US Classification:

342 25F, 342 25 A, 342 25 R

Abstract:

A moving radar generates a search mode synthetic aperture image of a patch having a principal scatterer. The boundaries of the patch are from Rto Rslant range and θto θazimuth angle. A computer motion compensates digital samples to obtain a motion compensated digital array. The motion compensated digital array is converted to a frequency array in the frequency domain K, KThe frequency array has a rectangular aperture extending ΔKand ΔK. Available samples from the frequency array are computed using a Range Migration Algorithm including a Stolt interpolation. Usable samples are identified from the available samples using one or more criteria. Usable samples are removed from available samples to obtain incomplete samples. Features related to the patch having a principal scatterer are extracted from the usable samples. The features are used to extrapolate extrapolated samples from the usable samples.