(A) study of beamforming methods for BDMA and radar systems employing analog beamformer

Abstract

Many of modern radar systems and BDMA systems employ antenna arrays with thousands ofanetnnas. These antennas are usually grouped into a few subarrays or beams through the process ofbeamspace transformation, to estimate the angle of a target. The angle estimation accuracy is depend on the array antenna structure and beamforming method. In this dissertation, we propose various beamforming methods for beam division multiple access (BDMA) systems and radar systems employing analog beamformer. In the first part, a new method is presented to provide an effective means for measuring the angles of signals in a subarray architecture where only one receiver is employed. This is analogous to the combination of the subarray and switched array where a receiver is installed at one subarray. However, it is different in that it use all the signals in each array element and time.Unlike traditional phased array system where the phase of the signal is controlled to a fixed value by a phase shifter at each array element for a specified direction, the phase of signals is controlled by a function of time in the proposed approach. To do this, we first formed antenna beams by the use of the control of phase shifters in the temporal domain based on the developed method. As a result, the signal on each beam reveals frequency dependent characteristic. Then the DOAs of the multiple signals can be estimated using a proper filter bank and conventional angle estimation algorithm. Although we concentrate our concern to angle estimation, it will also be utilized in an adaptive beamforming to cancel some interferences. In the second part,we consider a simple but pragmatic beamspace transformation that only allows beam steering, and present a technique of finding optimal steering angles that minimize the Cramer-Rao bound (CRB) for angle estimation. The CRB and mean squared error (MSE) of the angle estimate using the resulting optimal steering angles are compared with those using the widely used DFT-based beam steering. And The CRBs and mean squared errors (MSE) of two commonly used array antenna geometries, uniform linear array (ULA) and uniform arc array (UA), are compared to determinewhich one is better to cover wide sector.