The design of the RF over fiber signal transport system for the ALPACA receiver is described, with particular attention to the strict noise requirements as well as dynamic range considerations. Also discussed are analytical tools for analyzing dynamic range in the context of RFI-rich radio astronomy observational settings, including formulas for maximum interference to noise ratios and a simulation framework for predicting distortion levels. Phase and gain stability measurements of the signal transport system are presented, including the effects of the multi-strand armored fiber optic cable. The resulting system meets design requirements, with equivalent noise temperature below 900 K in 90° F ambient air, resulting in less than 1 K contribution to the system noise temperature. Typical gain is 31-37 dB, and gain differences between channels are stable within 0.25 dB in 90° F conditions. Phase drift between channels due to electronics remains below 1° at room temperature, and below 1.3° in a warm environment. The fiber optic cable is predicted to cause phase changes between channels of no more than 1.3° per °C. Typical spurious free dynamic range is 99 dB·Hz^(⅔), and distortion levels for normal RFI conditions at Arecibo are expected to be 28 dB below the system noise floor.

The design of the RF over fiber signal transport system for the ALPACA receiver is described, with particular attention to the strict noise requirements as well as dynamic range considerations. Also discussed are analytical tools for analyzing dynamic range in the context of RFI-rich radio astronomy observational settings, including formulas for maximum interference to noise ratios and a simulation framework for predicting distortion levels. Phase and gain stability measurements of the signal transport system are presented, including the effects of the multi-strand armored fiber optic cable. The resulting system meets design requirements, with equivalent noise temperature below 900 K in 90° F ambient air, resulting in less than 1 K contribution to the system noise temperature. Typical gain is 31-37 dB, and gain differences between channels are stable within 0.25 dB in 90° F conditions. Phase drift between channels due to electronics remains below 1° at room temperature, and below 1.3° in a warm environment. The fiber optic cable is predicted to cause phase changes between channels of no more than 1.3° per °C. Typical spurious free dynamic range is 99 dB·Hz^(⅔), and distortion levels for normal RFI conditions at Arecibo are expected to be 28 dB below the system noise floor.

Recent developments in the field of phased array feeds for radio astronomical reflector antennas, have opened a new frontier for array signal processing for radio astronomy observations. The goal is to replace single horn feeds with a phased array feed, so as to enable astronomers to cover more sky area in less time. The development of digital backend signal processing systems has been a major area of concentration for the development of science-ready phased array feeds for radio astronomers. This thesis focuses on the development of analog down-converter receivers and an FPGA-based digital backend for real-time data processing and analysis support for phased array feeds. Experiments were conducted with new receiver boards and both single-polarization and dual-polarization phased array feeds at the Arecibo Observatory, Puerto Rico and at the 20-meter telescope at Green Bank, WV, and results were analyzed. The experiments were performed as a part of a feasibility study for phased array feeds. The new receiver boards were developed as an upgrade to the earlier connectorized receivers as the number of input channels increased from 19 to 38 and space constraints arose due to the large size of the earlier receivers. Each receiver card has four independent channels on it. The receiver cards were found to have lower cross-coupling between the channels in comparison to the earlier receivers. The development of a FPGA-based real time digital backend focused on a real-time spectrometer, beamformer and a correlator for all the 64-channels using a x64 ADC card and ROACH FPGA boards. The backend can plot results in real time and can stream and store the data on the computers for purpose of post-processing and data analysis. The design process uses libraries and blocks provided by the Center for Astronomy Signal Processing and Electronics Research (CASPER) community.

Radio astronomy is used to study stars, galaxies, black holes and gas clouds radiation at radio frequencies. Detecting extremely weak signals from deep space radio sources requires high sensitive feed system associated with large dish antennas. The key figure of merit is survey speed, or the time required to map a region of the sky to a given source flux density. Survey speed is proportional to the frequency bandwidth, the field of view or observable region of the sky, and the squared sensitivity, where sensitivity is related to reflector aperture efficiency and system noise temperature. Compared to the traditional single feed, phased array feeds with significantly expanded field of view are considered as the next generation feed for radio telescope. This dissertation outlines the design, analysis and measurement of high sensitivity L-band and mm-wave phased array feeds for the 100-meter Green Bank Telescope. Theoretical works for radio astronomy includes design guideline for high sensitivity phased array feed, fundamental frequency bandwidth limit, array antenna loss influenced by mutual coupling and beamformer coefficients and possibility of superdirectivity for radio telescopes and other antennas. These study are helpful to understand and guide the design of a phased array feed system. In the absence of dish antennas, sparse phased arrays with aperiodic structure have been developed for satellite communications. A compromise between the peak side lobe level, array element density, directivity and design complexity is studied. We have found that the array peak side lobe level can be reduced by enhancing the array element direction at the main lobe direction, increasing the array element density and enlarging the array size. A Poynting streamline approach develops to understand the properties of a receiving antenna and the mutual coupling effects between array elements. This method has been successfully used to generate effective area shape for many types of antennas and guide the design of a superdirective antenna. Motivated by this method, a superdirective antenna is experimental demonstrated.

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.

Research institutions around the globe are developing phased array feed (PAF) systems for wide-field L-band radio astronomical observations. PAFs offer faster survey speeds and larger fields of view than standard single-pixel feeds, which enable rapid sky surveys and significantly increased scientific capability. Because deep space astronomical signals are inherently weak, PAF systems must meet stringent noise and sensitivity requirements. Meeting these requirements requires detailed modeling of the phased array itself as well as the reflector it is mounted on. This thesis details a novel approach to dual-pol PAF design that models the array and reflector as a complete system in order to achieve a more optimal sensitivity and system noise temperature. The design and construction of two arrays designed using this technique is discussed. The implementation of a data acquisition system to receive data from the first of these arrays is also detailed. Polarization state information plays an important role in understanding cosmological processes for many deep space sources. Because of phase and gain imbalances in the LNAs and receiver chains calibration is required for accurate measurement of polarization by phased array feeds. As a result accurate polarimetric calibration techniques are essential for many observations. Existing polarimetric calibration methods are based on assumptions about the form of the system Mueller matrix that limit the generality of the method or require long observations of a polarized source which is time-consuming for multiple PAF beams. This thesis introduces a more efficient method of calibration that uses only three snapshot observations of bright astronomical calibrator sources, one unpolarized and two partially polarized. The design of an engineering array for the Green Bank Telescope is discussed. Measured results from a prototype element are presented along with simulated on-reflector results for the full array. Simulations predict that the array will be the highest sensitivity dual pol feed built by the Radio Astronomy Systems group at Brigham Young University to date.

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.

The Brigham Young University (BYU) Radio Astronomy Systems group, in collaboration with the National Radio Astronomy Observatory (NRAO), the Center for Astrophysics at West Virginia University (WVU), and the Green Bank Observatory (GBO) have developed, and commissioned, a broadband real-time digital back end processing system for a 38-element phased array feed (PAF) with 150 MHz of instantaneous bandwidth. This system is capable of producing coarse and fine channel correlations, and implements a real-time beamformer that forms 7 simultaneous dual-polarized beams. This thesis outlines the hardware and software development for the digital back end and presents on-telescope commissioning results. This system has been measured to provide an unprecedented low Tsys/η noise level of 28 K and can perform maps of galactic hydrogen observations in a fraction of the time of a conventional single horn feed. The National Radio Astronomy Observatory (NRAO) has recently announced the concept and development of the next generation Very Large Array (ngVLA), a large interferometric array consisting of 300 radio telescopes and longest baseline (distance between a pair of antennas) of 300 km. Large interferometric arrays have been shown to attenuate radio frequency interference (RFI) because it is decorrelated as it propagates across long baselines. This is not always sufficient, especially with dense core array geometries and with the ever-increasing amount of strong RFI sources. Conventional RFI projection-based mitigation techniques have performed poorly on large interferometers because of covariance matrix estimation error due to decorrelation when identifying interference subspace parameters. This thesis presents an algorithm that overcomes the challenge of decorrelation by applying subspace projection via subarray processing (SP-SAP). Each subarray is designed to have a set of elements with high mutual correlation in the interferer for better estimation of subspace parameters. In simulation, compared to the former approach of applying subspace projection on the full array, SP-SAP improves mitigation of the RFI on the order of 9 dB. A signal of interest is shown then to be observable through the RFI in a full synthetic image.

The Brigham Young University (BYU) Radio Astronomy group, in collaboration with Cornell University, the University of Massachusetts, and the National Radio Astronomy Observatory (NRAO), have in recent years developed and deployed PAF systems that demonstrated the advantages of PAFs for astronomy. However, these systems lacked the necessary bandwidth and acquisition times to be scientifically viable. This thesis outlines the development of a 20-MHz bandwidth system that can acquire for much longer periods of time and across much larger bandwidths than previous BYU systems. A report of the deployment of this system on the 305-meter reflector at the Arecibo Observatory in Puerto Rico is also summarized.The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is currently constructing a PAF-equipped synthesis imaging array named the Australian Square Kilometre Array Pathfinder (ASKAP) that offers great promise for widening FOVs and enhancing RFI mitigation techniques. Previous work in RFI mitigation has demonstrated effective cancellation for synthesis imaging arrays under the assumption that the processing bandwidth is narrowband and correlator dump times are short. However, these assumptions do not necessarily reflect real-world instrument limitations. This thesis explores simulated adaptive array cancellation algorithm effectiveness as applied on the ASKAP instrument given realistic bandwidths and correlator dump times. The results demonstrate that active RFI mitigation performed across long baselines is largely ineffectual.

Phased array feeds (PAFs) are a promising new technology for astronomical radio telescopes. While PAFs have been used in other fields, the demanding sensitivity and calibration requirements in astronomy present unique new challenges. This dissertation presents some of the first astronomical PAF results demonstrating the lowest noise temperature and highest sensitivity at the time (66 Kelvin and 3.3 m^2/K, respectively), obtained using a narrowband (425 kHz bandwidth) prototype array of 19 linear co-polarized L-band dipoles mounted at the focus of the Green Bank 20 Meter Telescope at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia. Results include spectral line detection of hydroxyl (OH) sources W49N and W3OH, and some of the first radio camera images made using a PAF, including an image of the Cygnus X region. A novel array Y-factor technique for measuring the isotropic noise response of the array is shown along with experimental measurements for this PAF. Statistically optimal beamformers (Maximum SNR and MVDR) are used throughout the work. Radio-frequency interference (RFI) mitigation is demonstrated experimentally using spatial cancelation with the PAF. Improved RFI mitigation is achieved in the challenging cases of low interference-to-noise ratio (INR) and moving interference by combining subspace projection (SP) beamforming with a polynomial model to track a rank 1 subspace. Limiting factors in SP are investigated including sample estimation error, subspace smearing, noise bias, and spectral scooping; each of these factors is overcome with the polynomial model and prewhitening. Numerical optimization leads to the polynomial subspace projection (PSP) method, and least-squares fitting to the series of dominant eigenvectors over a series of short term integrations (STIs) leads to the eigenvector polynomial subspace projection (EPSP) method. Expressions for the gradient, Hessian, and Jacobian are given for use in numerical optimization. Results are given for simulated and experimental data, demonstrating deeper beampattern nulls by 6 to 30dB. To increase the system bandwidth toward the hundreds of MHz bandwidth required by astronomers for a fully science-ready instrument, an FPGA digital backend is introduced using a 64-input analog-to-digital converter running at 50 Msamp/sec and the ROACH processing board developed at the University of California, Berkeley. International efforts to develop digital back ends for large antenna arrays are considered, and a road map is proposed for development of a hardware correlator/beamformer at BYU using three ROACH boards communicating over 10 gigabit Ethernet.