The Boeing Company

The United States of America As Represented by the Administrator of the

Kuang Yung Liu

Jennifer L Vollbrecht

Chialin Wu

Lauriston Chin Wah

David L Crampton

Peter Y Cheung

A method and apparatus for reducing intermodulation distortion is disclosed. In one embodiment, the method comprises the steps of accepting a sampled input signal V(t) wherein the input signal V(t) comprises a plurality of peaks; determining n peaks V,V, . . . Vof the sampled input signal V(t) exceeding a clip value Vat times t, t, . . . t; and modifying the sampled input signal V(t) by weighting the n peaks V,V, . . . ,Vexceeding the clip value Vof the sampled input signal V(t) by a function b(t) wherein b(t) is either a hard limiting function or b(t)=f(a, a, . . . a;t&#x2212;t,t&#x2212;t, . . . t&#x2212;t), wherein a,a, . . . aare weight values corresponding to the n peaks V, V, . . . V, and f(t&#x2212;t,t&#x2212;t, . . . t&#x2212;t) is a smooth shaping function. Intermodulation performance is then selectively improved in selected sub-bands by notch filtering prior to application to the non-linearity.

Method and apparatus for low intermodulation distortion amplification in selected bands

A synthetic aperture radar system (SAR) having a range correlator (10) is provided with a hybrid azimuth correlator (12) for correlation utilizing a block-pipelined Fast Fourier Transform (12a) having a predetermined FFT transform size with delay elements (Z) for so delaying SAR range correlated data as to embed in the Fourier transform operation a corner-turning function as the range correlated SAR data is converted from the time domain to a frequency domain. A transversal filter (12b) connected to receive the SAR data in the frequency domain, and from a generator (14b) a range migration compensation function, D, to a programmable shift register (30) for accurate range migration compensation; weights, W.sub.i, to multipliers (35-38) for interpolation, and an azimuth reference function, .phi..sub.j, in the frequency domain to a multiplier 42 for correlation of the SAR data. Following the transversal filter is a block-pipelined inverse FFT (12c) used to restore azimuth correlated data in the frequency domain to the time domain for imaging. The FFT transform size is selected to accommodate the different SAR azimuth aperture lengths, number of looks and prefiltering requirements.

Pipelined digital SAR azimuth correlator using hybrid FFT/transversal

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Los Angeles, CA, United States of America

Kuang Yung Liu