With conventional pulse-echo ranging approaches it is diffcult to obtain un accurate range measurement needed by a proximity ultrasonic sensor system owing to the limited bandwidth of the transducer. A continuous-wave multifreouencv ranging method is presented to accurately measure the proximity distance for an ultrasonic distance sensor system A novel time delay estimator is derived based on a nonlinear least-squares-fitting criterion for the case where the received signal amplitude is non-negative owing to the acoustically hard reflection To minimise the highly oscillatory cost function an effcient two-stage estimation algorithm is proposed Numerical results show that the estimation algorithm can approach the Cram6r-Rao bound as the signal-to-noise ratio increases.

A computationally efficient algorithm, referred to as DS-WRELAX, is proposed for the delay and Doppler scale estimation of multiple moving targets. DS-WRELAX can approach the corresponding Cramer-Rao bounds and exhibits much better convergence properties than existing algorithms.

A new automatic target recognition (ATR) scheme based on oncdimensioaal high range resolution profiles is presented, which features joint range alignment and classification This meThod CKI also be used to form mean-or eigen-templates to fianher improve the ATR performance Experimental results are provided to demonstcate the performance of the new algorithm.

In modern radar, sonar and wireless communication systems digital beamforming technology based on sensor arrays is widely used to suppress unwanted interfering signals and detect interested target signals．Beam pattern synthesis for arbitrary arrays and robust beamforming for imperfect arrays are two crucial technical issues associated with digital beamforming．In a complex volumetric underwater acoustic transducer array, due tostructural shadowing and scattering. the practical beam pattern significantly deviates from its designed pattern, which would greatly degrade the detection and direction. finding performance of the sonar system. An efficient method is proposed to design beam patterns for arbitrary arrays and is applied to robust beamforming for this sonar system. Sea experimental results show that the proposed robust beamforming method achieves a much lower sidelobe level and a much higher direction. finding accuracy than the conventional beamforming technique.

Space-time adaptive processing (STAP) for airborne early warning radar has been a very active area of research since the late 1980's. An airborne rectangular planar array antenna is usually configured into subarrays and then partial adaptive processing is applied to the outputs of these subarrays. In practice, three kinds of errors are often encountered, i.e., the array gain and phase errors existing in each element, the channel gain and hase errors, and the clutter covariance matrix estimation errors due to insufficient secondary data samples. These errors not only degrade the clutter suppression performance, but also cause the adapted array patterns to suffer much distortion (high sidelobes and distorted mainbeams), which may result in the rise of falsealarm probability and make the adaptive monopulse tracking and sidelobe blankering more difficult. In this paper, the causes of the above three kinds of errors to array pattern distortion are discussed and a novel quadratic soft constraint factored approach is proposed to precisely control the peak sidelobe level of adapted patterns. The soft constraint factor can be determined explicitly according to the peak sidelobe level desired and the known or desired tolerant error standard deviations. Numerical results obtained by using high-fidelity simulated airborne radar clutter data are provided to illustrate the performance of the proposed approach. Although the method is presented for STAP, it can be directly applied to the conventional adaptive beamforming for rectangular planar arrays used to suppress jammers.