Two-dimensional angular parameter estimation for noncircular incoherently distributed sources based on an L-shaped array

In this paper, a two-stage reduced-rank estimator is proposed for two-dimensional (2D) direction estimation of incoherently distributed (ID) noncircular sources, including their center directions of arrival (DOAs) and angular spreads, based on an L-shaped array. Firstly, based on the first-order Taylor series approximation, a noncircularity-based extended generalized array manifold (GAM) model is established. Then, the 2D center DOAs of incident ID signals are obtained separately with the noncircularity-based generalized shift-invariance property of the array manifold and the reduced-rank principle. The pairing of the two center DOAs is completed by searching for the minimum value of a cost function. Secondly, the 2D angular spreads can be obtained in closed-form solution from the central moments of the angular distribution. The proposed estimator achieves higher accuracy in angle estimation that manages more sources and shows promising results in the general scenario, where different sources possess different angular distributions. Furthermore, the approximate noncircular stochastic Cramer-Rao bound (CRB) of the concerned problem is derived as a benchmark. Numerical analysis proves that the proposed algorithm achieves better estimation performance in both 2D center DOAs and 2D angular spreads than an existing estimator

Anti-Jam GPS Controlled Reception Pattern Antennas for Man-Portable Applications

Military GPS receivers provide crucial information to soldiers in the field, however, the performance of these devices is degraded by in band RF interference, making GPS susceptible to jamming. Anti-jam techniques for aircraft and vehicular platforms have been developed, but at present there is no system for dismounted soldiers. There is a need for an anti-jam system which meets the demands of a dismounted soldier and conforms to the size, weight, and power requirements of a portable device. A controlled reception pattern antenna, or CRPA, is a potential solution for jammer mitigation. These devices work by steering reception pattern nulls toward the jammer direction, reducing the jammer power which reaches the GPS receiver. Prior CRPA realizations have been designed for use on vehicular and aircraft applications, however, these platforms do not suffer from the same limitations as a man-portable CRPA. Three considerations which are more pertinent for man-portable designs than prior work are (i) distributed antenna element positions and orientations dynamically change during use changing the reception pattern characteristics, (ii) the user is lower to the ground and moves through the environment meaning that multipath propagation can have a greater effect on CRPA performance, and (iii) the size weight and power constraints for a portable system limit the number of antenna elements reducing the degrees of freedom that can be used for cancellation. To address these challenges, a framework for man-portable CRPA modeling is presented. This includes development of efficient modeling methods which enable investigations into element perturbations to address the dynamic orientation problem. These and other methods are presented in Chapter 3, along with a discussion of the relative strengths and weaknesses of each. Additionally, a mixed scattering channel model is applied to the CRPA reception patterns, combining diffuse and specular reflection in Chapter 4. Discussion of this model centers around the eigenvalues of the signal covariance matrix and the effect of coherence between multipath components. Following this, Chapter 5 examines the performance of polarimetric CRPAs and space-time adaptive processing for man-portable CRPAs with limited degrees of freedom