Master of Science, University of Akron, 2017, Electrical Engineering

Radio frequency (RF) antenna array beamforming based on electronically steerable wideband phased-array apertures find applications in communications, radar, imaging and radio astronomy. High-bandwidth requirements for wideband RF applications necessitate hundreds of MHz or GHz frame-rates for the digital array processor. Systolic array architectures are often employed in multi-dimensional (MD) signal processing for linear and rectangular antenna arrays. Thus, this research used a FPGA hardware platform, the ROACH-2, which is equipped with a Xilinx Virtex-6 SX475T FPGA chip, and which is widely used in the field of radio astronomy. The research concentrated on the prospects of implementation of systolic array based MD beamformers on the ROACH-2, and on methods of extending the operating frequency to GHz range by using polyphase structures. The proposed systolic array architectures employ a differential form 2-D IIR frequency planar beam filter structure which is low in hardware utilization. The study highlights techniques that can be used to overcome the limitations of the ROACH-2 signal processing platform to achieve high operating frequencies.

Committee: Arjuna Madanayake (Advisor); Subramaniya Hariharan (Committee Member); Joan Carletta (Committee Member) Subjects: Communication; Electrical Engineering; Engineering

Master of Science, University of Akron, 2015, Electrical Engineering

Linear and rectangular aperture arrays combined with multidimensional (MD) signal processing techniques enable directional enhancement of plane waves by creating highly directional radio frequency (RF) beams. Applications of such space-time filtering (beamforming) techniques can be found in areas such as radar, mobile communication, cognitive radio and radio astronomy. Main challenges in existing beamforming systems include high computational and hardware complexity, low operational bandwidth, and limited spatial selectivity. In this thesis, we employ the network resonant infinite impulse response (IIR) digital beam filter towards the performance enhancement of the existing beamforming systems and its related applications in terms of hardware complexity, spatial selectivity and operational bandwidth. Inherent properties of IIR beam filters, such as \emph{low complexity, higher operational bandwidth, multiple input multiple output (MIMO) nature, recursive structure and electronically steerablity} lead to improve directivity properties of the conventional beamformers and enable less complex directional enhancement for wideband applications. Low complexity directional spectrum sensing and feature extraction approach is proposed by combining network resonant beam filters with cyclostationary feature detectors. Spatial selectivity of the conventional beamformer is significantly enhanced by employing a MD MIMO beam filter as a pre-filter to the existing system. Furthermore, an electronically steerable transmit-beamformer based on space-time network resonant IIR discrete systems is proposed for wideband directed energy applications.

Committee: Arjuna Madanayake (Advisor); Kye-Shin Lee (Committee Member); Igor Tsukerman (Committee Member) Subjects: Engineering

Doctor of Philosophy (PhD), Ohio University, 1987, Electrical Engineering & Computer Science (Engineering and Technology)

Adaptive array and spread-spectrum techniques are widely used for the suppression of interference in many communications applications. In this dissertation, an improved adaptive filtering algorithm is investigated to synthetically overcome some of the problems associated with the conventional least-mean-square (LMS) algorithm, which requires generating a reference signal, and is not effective in coherent interference rejection. The results for the modified LMS algorithm, which we call the ZMS algorithm in this work, shows several advantages over the conventional LMS algorithm including:(1) reference signal generation is not required,(2) input interference signals are not required to be uncorrelated with the desired target signal, (3) convergence range is independent of the desired signal power, and (4) it converges rapidly and achieves small mean-square error. The primary characteristics of the ZMS algorithm are the elimination of the reference signal in the weight control loop and the decorrelation of the interference signal from the array input signal, by separating them using spatial or frequency filtering prior to adaptive minimization procedure. Two types of ZMS beamformers were investigated and simulated: the FIR notch filtered ZMS beamformer (FIR-ZMS) and the spatial notch filtered ZMS beamformer (SP-ZMS). Simulation results confirm the theoretical predictions of the ZMS algorithm for the rejection of coherent and/or non-coherent interference. It is shown that the ZMS algorithm achieves rapid convergence and small mean-square error in comparison with the LMS algorithm. Even in worst case situations where the desired signal information is not available and the interference is at the same frequency as the target signal, the SP-ZMS beamformer effectively rejects the coherent interference and reproduces the desired target signal. The FIR-ZMS beamformer is not effective in a worst case coherent jammer scenario. Signal leakage out of the input notch filter in the Z (open full item for complete abstract)

Committee: Joseph Essman (Advisor) Subjects: