The goal of the research reported in this thesis is to establish the feasibility of a novel optical architecture for an optical route & select circuit switch suitable for implementation as a photonic integrated circuit. The proposed architecture combines Optical Phased Array (OPA) switch elements implemented as multimode interference coupler based Generalised Mach-Zehnder Interferometers (GMZI) with a planar Lüneburg lens-based optical transpose interconnection network implemented using graded metamaterial waveguide slabs. The proposed switch is transparent to signal format and, in principle, can have zero excess insertion loss and scale to large port counts. These switches will enable the low-energy consumption high capacity communications network infrastructure needed to provide environmentally-friendly broadband access to all. The thesis first explains the importance of switch structures in optical communications networks and the difficulties of scaling to a large number of switch ports. The thesis then introduces the Talbot effect, i.e. the self-imaging of periodic field distributions in free space. It elaborates on a new approach to finding the phase relations between pairs of Talbot image planes at carefully selected positions. The free space Talbot effect is mapped to the waveguide Talbot effect which is fundamental to the operation of multimode interference couplers (MMI). Knowledge of the phase relation between the MMI ports is necessary to achieve correct operation of the GMZI OPA switch elements. An outline of the design procedures is given that can be applied to optimise the performance of MMI couplers and, as a consequence, the GMZI OPA switch elements. The Lüneburg Optical Transpose Interconnection System (LOTIS) is introduced as a potential solution to the problem of excessive insertion loss and cross-talk caused by the large number of crossovers in a switch fabric. Finally, the thesis explains how a Lüneburg lens may be implemented in a graded ‘metamaterial’, i.e. a composite material consisting of ‘atoms’ arranged on a regular lattice suspended in a host by nano-structuring of silicon waveguide slabs using a single etch-step. Furthermore, the propagation of light in graded almost-periodic structures is discussed. Detailed consideration is given to the calibration of the local homogenised effective index; in terms of the local parameters of the metamaterial microstructure in the plane and the corrections necessary to accommodate slab waveguide confinement in the normal to the plane. The concept and designs were verified by FDTD simulation. A 4×4 LOTIS structure showed correct routing of light with a low insertion loss of -0.25 dB and crosstalk of -24.12 dB. An -0.45 dB excess loss for 2D analysis and an -0.83 dB insertion excess loss for 3D analysis of two side by side metamaterial Lüneburg lenses with diameter of 15 μm was measured, which suggests that the metamaterial implementation produces minimal additional impairments to the switch.

For a linear array, the excitation coefficients of each element and its geometry play an important role, because they will determine the radiation pattern of the given array. Side Lobe Level (SLL) is one of the key parameters to evaluate the radiation pattern of the array. Generally speaking, we desire SLL to be as low as possible. For the linear array with uniform spacing, there are some classic methods to calculate the excitation coefficients to make the radiation pattern satisfy the given requirements. For the linear array with non-uniform spacing, linear programming and particle swarm optimization are proposed to calculate the excitation coefficients to make the array get minimum SLL in this thesis. They are demonstrated for symmetric and asymmetric array in the first part of this thesis. In the second part of this thesis, a simple method is proposed for correcting excitation coefficients of a linear phased array. This proposed method corrects the coefficients through using the Normalized Least Means Squares(NLMS) algorithm, dither signal and a near-field sensor being used for sensing the field emitted by the array. The advantage of this proposed method is that it avoids the problem of estimating the largest eigenvalue of the coefficient matrix to get optimal step size. Its robustness in different environments is demonstrated as well as the effect of noise with various Signal-to-Noise Ratio (SNR), and mutual coupling. In addition, the effect of using discrete dither signal to the array is considered, because the continuous dither signal cannot be generated in practice.

Radio astronomy, the survey and study of naturally occurring astronomical radio signals, is a challenging field in terms of engineering requirements. The typical astronomical signal of interest is incredibly faint, resulting in very low signal-to-noise ratios (SNRs) on the order of -30 dB or lower. To detect such signals, one must have an uncommonly low and stable receiver noise temperature, high gain through large aperture reflectors, and state-of-the-art signal processing algorithms. One must also be able to mitigate the effects of interference, the presence of which, even if extremely weak, can completely mask the faint astronomical signals of interest. To this end, this work presents the development of and results from a new broadband phased array feed (PAF) named the Focal L-Band Array for the Green Bank Telescope (FLAG). This instrument is able to form multiple simultaneous beams to survey a large patch of sky instantaneously, and has a minimum system noise temperature (Tsys) of 16.83 K. This PAF also has the potential to use spatial filtering techniques to place pattern nulls in the direction of interfering signals through the use of an orthogonal projection. This work will also present an improved method for computing an orthogonal projection operator, which is able to place a spatially broad null in the direction of a moving RFI source. A formal derivation of some detection and estimation theory properties for astronomical radio transients is also presented, which formalization is lacking within the astronomical community. This includes maximum-likelihood detectors and estimators and a Cramér Rao bound (CRB) analysis of astronomical transient parameters.

Radio frequency interference is an ever growing problem in the wireless community. This dissertation presents methods to reduce interference for vehicular multi-antenna devices. This document is organized into two parts: the main chapters and the appendices. The main chapters present research conducted primarily by the author. These deserve the reader's primary attention. The appendices showcase contributions made by the author serving in a supporting role to projects led by others and/or do not fit the vehicular theme. These should receive secondary attention. The main chapter contributions are summarized as follows. A device was created that provides over 105 dB of transmit to receive isolation in a full duplex printed circuit board radio. This technology can improve the effective range of vehicular radar systems and increase the bandwidth of full duplex communication schemes for vehicles. The technologies involved are compatible with existing circuit board topologies and are mindful of the size and weight requirements for vehicular use. This isolation performance pushes the state of the art for printed circuit board designs and provides greater capability for these kinds of devices. Recent system on chip computing architectures are opening new pathways for integrating phased array technologies into a single chip. The computer engineering required to configure these devices is beyond the capabilities of many vehicle systems engineers, inviting the author to use one to implement a 16 antenna adaptive beamformer for GPS. The adaptive beamformer can combat multipath bounces and malicious spoofing from ground sources. The high rate analog conversion architecture eliminates the local oscillator distribution to simplify the analog front end to an active antenna. This allows vehicular phased arrays to use smaller footprints and suggests that multi-antenna beamforming devices may be easier to deploy on small to midsized vehicles. Bench tests of the beamformer indicate it can adapt to the environment and increase the received signal strength suggesting it can improve GPS quality for active deployments. The bank of subspace projection beamformers is a popular choice for mitigating interference in digital phased array receivers. A method was discovered that maps that matrix operator into a circuit topology that is simple to implement in an analog circuit and cancels across the entire bandwidth simultaneously. This can offload computational interference mitigation from the signal processor while still allowing secondary multi-pixel digital beamforming downstream. This beamformer was analytically connected to the body of phased array literature and studied to estimate practical error bounds and design methods of calibration.

Weather monitoring and forecasting systems have witnessed rapid advancement in recent years. However, one of the main challenges faced by these systems is poor coverage in lower atmospheric regions due to earth's curvature. The Engineering Research Center for the Collaborative Adaptive Sensing of the Atmosphere (CASA) has developed a dense network of small low-power radars to improve the coverage of weather sensing systems. Traditional, mechanically-scanned antennas used in these radars are now being replaced with high-performance electronically-scanned phased-arrays. Phased-Array radars, however, require large number of active microwave components to scan electronically in both the azimuth and elevation planes, thus significantly increasing the cost of the entire radar system. To address this issue, CASA has designed a "Phase-Tilt" radar, that scans electronically in azimuth and mechanically in elevation. One of the core components of this system is the Phased-Array controller or the Array Formatter. The Array Formatter is a Field Programmable Gate Array (FPGA)-based master controller that translates user commands from a computer to control and timing signals for the radar system. The objective of this thesis is to design and test an FPGA-based Array Formatter for CASA's Phase-Tilt radar system.

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In recent years, the Brigham Young University (BYU) Radio Astronomy Systems group has developed phased-array feeds and the data acquisition processing systems necessary to perform radio astronomy observations. This thesis describes the development and testing of a real-time digital beamforming system that reduces both the time required to process phased-array feed data and the disk space used to record this data compared to post-processing beamforming systems. A real-data experiment is also discussed in this thesis, which focuses on some of the data post-processing required for one of BYU's data acquisition systems.Radio-frequency interference mitigation techniques for phased-array feed radio astronomy have been studied for several years, but the effect that these techniques have on weak-signal detection is not well understood. This thesis provides analysis of a simulated weak-source observation for the Green Bank 20-meter telescope and BYU 19 element phasedarray feed with radio-frequency interference present. Interference mitigation techniques are shown to reduce the detectability of weak sources compared with the no interference case, but it is also shown that a weak source can be detected that would otherwise be masked by interference.

One of the many challenges in radio astronomy is the ability to make accurate measurements quickly. In recent years engineers and astronomers have begun implementing phased array feeds (PAFs) as a way to negate the long observation times required by single antenna feeds. Unfortunately, large mutual coupling and other loss terms result in low sensitivity, restricting PAF usefulness in on dish observation. This thesis addresses several ways to reduce mutual coupling and maximize sensitivity for PAFs in radio astronomy. Antenna design of this magnitude requires accurate modeling capabilities. To this end, electromagnetic software models and low loss component designs are verified and validated with measured data. This process required the construction of a 50 Ω matched dipole and measurements on a network analyzer at Brigham Young University. The design and optimization of several single and dual polarization hexagonal grid arrays of 19 and 38 elements respectively are also described. Model figures of merit are compared with measurements taken on the 20-Meter dish at the National Radio Astronomy Observatory (NRAO) in Green Bank, WV and the 300 meter dish at the Arecibo Observatory in Arecibo, PR. Although some unexplained discrepancies exist between measured and model datasets, the dual pol cryocooled kite array described boasts the highest PAF sensitivity ever measured.

Phased arrays are electromagnetic antenna systems comprised of many radiating elements and processing electronics. Radiating elements are typically positioned in an orderly grid within the antenna aperture. In the receive mode of operation, radiating elements capture some of the signal energy from incoming radiation and guide these signals to processing electronics. Signals are filtered and amplified to maintain the desired sensitivity and complexly weighted using circuits with reconfigurable amplification gain and phase delay. Finally, all signals are combined. The summation of these complexly weighted spatial samples forms a spatial filter in the same way complexly weighted temporal samples establish a temporal filter in a finite impulse response discrete-time filter. Therefore, a phased array behaves like a spatial filter that strongly favors signals arriving from a specific direction. This favored direction represents the look angle of its beam, and the shape of the beam directly relates to the complex weights applied to the signals in the array. Analogous to the flexibility offered by digital filters, phased arrays enable agile beam steering, sidelobe control, and multiple independent beams. These capabilities have revolutionized radar, radioastronomy, and communication systems. Phased arrays have increasingly employed printed circuit board (PCB) fabrication techniques and processes to maximize array channel density, achieve lower profile, and minimize component integration cost. A few applications which leverage these qualities include low-cost radar, mobile satellite communication (SATCOM), and intelligence, surveillance, and reconnaissance (ISR). Further, PCB-based arrays readily accommodate advancements in highly integrated beamforming radio frequency integrated circuits (RFICs), multi-chip modules, and RF micro-electro-mechanical system (MEMS) device technologies. On a prior effort, an integrated unit cell design was developed for a PCB-based SATCOM array application. However, the design failed to meet the requirements. The primary objective of this work is to demonstrate an improved design using systematic microwave design techniques and modern analysis tools to meet the requirements for the same application. The proposed design must improve gain, bandwidth, size, and manufacturability over the prior design. Additionally, the design must be generally extensible to phased array implementations across the SHF band (3-30 GHz). This work discusses the advantages of phased arrays over continuous apertures (e.g. reflectors), reviews phased array theory, and proposes an improved unit cell design. The proposed design is 35% smaller than a dime and consists of an orthogonally-fed, slot-coupled stacked patch antenna and dual-stage branchline coupler implemented in a multilayer PCB. Within the operating band from 10.7 to 14.5 GHz, the design achieves an average return loss of 15 dB, a uniform radiation pattern with peak realized gain of 4.8 to 7.0 dBic, cross-polarization level below -17 dB, and stable performance in a closely-spaced array. When configured in an array, the design supports X/Ku-band SATCOM in full-duplex operation, electronically rotatable polarization, and a 47.5˚ grating lobe free conical scan range. Further, a Monte Carlo analysis proves the design accommodates tolerances of material properties and manufacturing processes, overcoming a major challenge in PCB-based high frequency antenna design.

The Advanced L-band Phased Array Camera (ALPACA) is a wide-field astronomical receiver that will be housed on the Green Bank Telescope (GBT). This instrument features a fully cryogenic 69-element phased array feed (PAF) front end and digital beamformer back end. It will provide a wide and continuous field of view at L-band and high sensitivity with a system noise temperature below 27 K. Transport of the received astronomical signals on 138 individual channels from prime focus of the GBT to the digital back end -- over a distance of 3 km -- will be provided by a custom RF-over-fiber (RFoF) system. The development and experimental verification of the custom RFoF link are presented. A 16-channel fiber receiver board custom-tailored for attachment to the Xilinx ZCU216 RF system-on-chip (RFSoC) provides minimum isolation of 36 dB between channels, a gain repeatability within 3 dB between channels, and less than 2 dBpp gain ripple. Full link tests on the RFoF system, including fiber transmitter and receiver, indicate less than .89 K contribution to ALPACA's overall system noise temperature while providing 25 to 46 dB of linear dynamic range and 30 to 38 dB of spurious-free dynamic range across 1300-1720 MHz. These results meet specified design requirements and affirm that the RFoF system will allow ALPACA to achieve high sensitivity and operate as a wide-field astronomical receiver on the GBT. Measurements and models of the ALPACA cross-dipole element and low noise amplifier are also given. The dipole model is resilient to changes to cryostat structure and the measurements and models of the as-built dipole are in agreement. The cryogenic low noise amplifiers perform as expected under room temperature operation in terms of gain, noise, and linearity. These results validate that the front-end technology is on track to meet specifications and will allow ALPACA to achieve instrument objectives.