Direct Data Domain Method Research Articles

Fast Heterogeneous Clutter Suppression Method Based on Improved Sparse Bayesian Learning

In order to deal with the problem space-time adaptive processing (STAP) performance degradation of an airborne phased array system caused by the serious shortage of independent and identical distributed (IID) training samples in the nonhomogeneous clutter environment, an improved direct data domain method based on sparse Bayesian learning is proposed in this paper, which only uses a single snapshot data of a cell under test (CUT) to suppress the clutter and has fast computational speed. Firstly, three hyper-parameters required to obtain the sparse solution are derived. Secondly, the comparative analysis of their iterative formulas is made, and the piecewise iteration of hyper-parameter that has an obvious influence on the computational complexity of obtaining sparse solution is presented. Lastly, with the approximate prior information of the target, the clutter sparse solution is given and its covariance matrix is effectively estimated to calculate the adaptive filter weight and realize the clutter suppression. Simulation results verify that the proposal can dramatically decrease the computational burden while keeping the superior heterogeneous clutter suppression performance.

Nonuniformly Spaced Array with the Direct Data Domain Method for 2D Angle-of-Arrival Measurement in Electronic Support Measures Application from 6 to 18 GHz

This paper introduces a 2D angle-of-arrival (AoA) estimator, which has a 6–18 GHz 7-element nonuniformly spaced array (NSA) and a Direct Data Domain- (D3-) based AoA algorithm for a 2D isotropic-element planar array (IEPA). A 2D calibration and data-transformation method is developed to convert the NSA data to the output of the IEPA, so that the NSA-measured data can be used in the D3 algorithm. Using the steering vector (SV) of the IEPA and the results derived from the D3 method, a new 2D AoA searching method is also developed, which offers frequency-independent performance defined by the probability of AoA estimation, when the required estimation accuracy and signal-to-noise ratio (SNR) are given. For the applications of electronic support measures, this paper also presents the use of precalculated SV and data-transformation matrix databases built on preselected frequency points and a 2D-angle grid that is close to uniformly distributed directions. The simulation results show that with good SNR (≥15 dB), the estimator can have 50% probability of AoA estimation with root mean square error (RMSE) less than or equal to 1° using just a few samples from the NSA. Moreover, the study focuses on the applications with low SNR by using more samples from the NSA. Results show that the estimator has 52% and 80% probabilities of AoA estimation with RMSE ≤1° and 5°, respectively, for phase- or frequency-modulated radar pulses, when the SNR is within [−10, 0] dB. The study also shows that the estimator prefers a circular-shaped planar array with a triangular interelement pattern, since it presents more symmetrical characteristics from different azimuth angles.

Direct data domain based method for ground moving target indication by bistatic airborne radar

Since the clutter received by bistatic airborne radar expresses severe range dependence,the clutter plus noise covariance matrix cannot be estimated accurately by clutter range samples,thus the performance of clutter suppression obtained by Space-Time Adaptive Processing(STAP) degrades greatly.To solve this problem,a method using Direct Data Domain(DDD) was proposed.Because DDD method obtains enough samples by spatial-temporal sliding only from one range gate,this method does not need to compensate for clutter range dependence.The simulation results verify the effectiveness of this method.

STAP for airborne radar with cylindrical phased array antennas

Cylindrical phased array antennas have three merits such as all-orientation space scanning, flexible search and track mode, and favorable antenna pattern etc. relative to common planar phased array antennas. In this paper, airborne radar with cylindrical phased array antennas is analyzed in terms of clutter model, clutter space–time distribution, and clutter suppression method, etc. Firstly, the mathematics model of airborne radar with cylindrical phased array antennas is given, and the properties of cylindrical array antenna pattern are analyzed. Secondly, the clutter spectrum distribution in space–time plane, clutter eigenvalue distribution, and clutter spectrum distribution at range are analyzed, respectively. Finally, three different clutter suppression methods from different points of view are presented, and they are as follows: space angular frequency shifting method (SAFS), HT CMT method, and direct data domain method based on joint target cancellation (DDD J). The simulation results illustrate the performance improvement achieved for airborne radar with cylindrical phased array antennas.

Matrix pencil method for simultaneously estimating azimuth and elevation angles of arrival along with the frequency of the incoming signals

In this paper we describe a method for simultaneously estimating the direction of arrival (DOA) of the signal along with its unknown frequency. In a typical DOA estimation problem it is often assumed that all the signals are arriving at the antenna array at the same frequency which is assumed to be known. The antenna elements in the array are then placed half wavelength apart at the frequency of operation. However, in practice seldom all the signals arrive at the antenna array at a single pre-specified frequency, but at different frequencies. The question then is what to do when there are signals at multiple frequencies, which are unknown. This paper presents an extension of the matrix pencil method to simultaneously estimate the DOA along with the operating frequency of each of the signals. This novel approach involves approximating the voltages that are induced in a three-dimensional antenna array, by a sum of complex exponentials by jointly estimating the direction of arrival (both azimuth and elevation angles) along with the carrier frequencies of multiple far-field sources impinging on the array by using the three-dimensional matrix pencil method. The matrix pencil method is a direct data domain method for approximating a function by a sum of complex exponentials in the presence of noise. The variances of the estimates computed by the matrix pencil method are quite close to the Cramer-Rao bound. Finally, we illustrate how to carry out the broadband DOA estimation procedure using realistic antenna elements located in a conformal array. Some numerical examples are presented to illustrate the applicability of this methodology in the presence of noise. It is shown that the variance decreases as the SNR increases. The Cramer-Rao bound for the estimators are also provided to illustrate the accuracy and the computational efficiency of this new methodology.