Phased array receivers are a set of antenna elements that are capable of forming multiple simultaneous beams over a field of view. In radio astronomy, the study of deep space radio sources, a phased array feed (PAF) is placed at the focus of a large dish telescope that spatially samples the focal plane. PAFs provide an increase in the field of view as compared to the traditional single pixel horn feed, thereby increasing survey speed while maintaining low sensitivity. Phased arrays are also capable of radio frequency interference (RFI) mitigation which is useful in both radio astronomy and wireless communications when detecting signals in the presence of interferers such as satellites. Digital signal processing algorithms are used to process and analyze data provided by phased array receivers. During the commissioning of the Focal-plane L-band Array feed for the Green Bank telescope (FLAG), sensitivity consistent with an equivalent system temperature below 18 K was measured. To demonstrate the astronomical capability of the receiver, a pulsar (PSR B2011+38) was detected, and an HI source (NGC4258) was mapped with the real-time beamformer and fine channel correlator, respectively. This work also details improvements made to the software of the FLAG digital backend such as the design and implementation of an algorithm to remove scalloping ripple from the spectrum of two cascading polyphase filter banks (PFB). This work will also provide a brief introduction to a model-based beam interpolation algorithm capable of increasing spatial resolution of radio source maps as well as reducing time spent performing calibration. The development of a phased array receiver digital back end for the Office of Naval Research (ONR) is also detailed. This broadband system will be capable of communication in hostile RFI-rich environments with the aid of a real-time RFI mitigation algorithm currently implemented in software. This algorithm will be compatible with other PAF receiver systems and will enable RFI mitigation in other applications such as radio astronomy. This work will provide details on the implementation of this algorithm, the development and modification of other system software as well as full system tests of the 150 MHz bandwidth receiver have been conducted and will be shown in this document.

Phased array receivers are a set of antenna elements that are capable of forming multiple simultaneous beams over a field of view. In radio astronomy, the study of deep space radio sources, a phased array feed (PAF) is placed at the focus of a large dish telescope that spatially samples the focal plane. PAFs provide an increase in the field of view as compared to the traditional single pixel horn feed, thereby increasing survey speed while maintaining low sensitivity. Phased arrays are also capable of radio frequency interference (RFI) mitigation which is useful in both radio astronomy and wireless communications when detecting signals in the presence of interferers such as satellites. Digital signal processing algorithms are used to process and analyze data provided by phased array receivers. During the commissioning of the Focal-plane L-band Array feed for the Green Bank telescope (FLAG), sensitivity consistent with an equivalent system temperature below 18 K was measured. To demonstrate the astronomical capability of the receiver, a pulsar (PSR B2011+38) was detected, and an HI source (NGC4258) was mapped with the real-time beamformer and fine channel correlator, respectively. This work also details improvements made to the software of the FLAG digital backend such as the design and implementation of an algorithm to remove scalloping ripple from the spectrum of two cascading polyphase filter banks (PFB). This work will also provide a brief introduction to a model-based beam interpolation algorithm capable of increasing spatial resolution of radio source maps as well as reducing time spent performing calibration. The development of a phased array receiver digital back end for the Office of Naval Research (ONR) is also detailed. This broadband system will be capable of communication in hostile RFI-rich environments with the aid of a real-time RFI mitigation algorithm currently implemented in software. This algorithm will be compatible with other PAF receiver systems and will enable RFI mitigation in other applications such as radio astronomy. This work will provide details on the implementation of this algorithm, the development and modification of other system software as well as full system tests of the 150 MHz bandwidth receiver have been conducted and will be shown in this document.

A phased array feed (PAF) provides a contiguous, electronically synthesized wide field of view for large-dish astronomical observatories. Significant progress has been made in recent years in improving the sensitivity of PAF receivers though optimizing the design of the antenna array, cryogenic cooling of the front end, and implementation of real-time correlation and beamforming in digital signal processing. FLAG is a 19 dual-polarized element phased array with cryogenic LNAs, direct digitization of RF signals at the front end, digital signal transport over fiber, and a real time signal processing back end with up to 150 MHz bandwidth. The digital back end includes multiple processing modes, including real-time beamforming, real-time correlation, and a separate real-time beamformer for commensal radio transient searches. Following a polyphase filterbank operation performed in field programmable gate arrays (FPGAs), beamforming, correlation, and integration are implemented on graphical processing units (GPUs) that perform parallelized operations. Parallelization greatly increases processing speed and allows for real-time signal processing. During a recent test/commissioning of FLAG, Tsys/efficiency of approximately 28 K was measured across the PAF field of view and operating bandwidth, corresponding to a system temperature below 20 K. To demonstrate the astronomical capability of the receiver, a pulsar (PSR B1937+21) was detected with the real-time beamformer. This thesis provides details on the development of the FLAG digital back end, the real-time beamformer, and reports on the commissioning tests of the FLAG PAF receiver developed by the National Radio Astronomy Observatory (NRAO), Green Bank Observatory (GBO), West Virginia University (WVU), and Brigham Young University for the Green Bank Telescope (GBT).

Astronomy large-scale surveys require instrumentation to minimize the time required to complete observations of large sections of the sky. Optimizing receiver systems has been achieved through reducing the system temperature primarily by advances in low-noise amplifier technology to a point that the internally generated noise is now fast approaching the quantum limit. Instead, reflector-coupled focal plane arrays are now used to increase the field of view (FoV) by employing either multi-element horn feeds or phased array feeds. Widely spaced (2-3 wavelengths diameter) horn feeds inefficiently sample the available focal plane radiation, thus requiring multiple imaging passes. Alternatively, a more efficient method is to use a narrow element (0.5 wavelengths diameter) phased array feed with a beamformer to produce overlapping beams on the sky, fully Nyquist sampling the focal plane with a single pass. The FoV can be further increased with additional phased array feed (PAF) antenna-receiver modules adding to the contiguous fully sampled region. A 5 x 5 K-band (18 - 26 GHz) single polarization modular PAF incorporating an antenna array of planar axially symmetric elements is designed, simulated, manufactured and tested. Each narrow width tapered slot antenna element has an independent receiver chain consisting of a cryogenic packaged monolithic microwave integrated circuit (MMIC) GaAs amplifier and a packaged MMIC down converting mixer. Synthesized beams and beamformer characteristics are presented. The PAF imaging system performance is evaluated by survey speed and compared to the industry standard, the single pixel feed (SPF). Scientifically, K-band is attractive because it contains numerous molecular transitions, in particular the rotation-inversion lines of ammonia. These transitions are excited in dense gas, and can be used to directly measure kinetic temperatures and velocities of protostars throughout the Galaxy. Depending on the line detected, gas of different temperatures can be probed. It is concluded that even with a higher system temperature, a PAF with sufficient number of synthesized beams can outperform a SPF in imaging speed by more than an order of magnitude. / Graduate

Creating accurate software based models of phased array feeds (PAFs) is one of many steps to successfully integrating PAFs with current and future radio telescopes, which is a goal of many groups around the globe. This thesis characterizes the latest models of a 19 element hexagonal PAF of dipoles used by the BYU radio astronomy research group and presents comparisons of these models with experimental data obtained using a prototype array. Experiments were performed at the NRAO site in Green Bank, West Virginia, and utilized the outdoor antenna test range and 20 meter radio telescope. Accurate modeling of the PAF requires modeling the signal and noise characteristics of the array, which is a computationally large problem. It also requires accurate modeling of the noise contribution of the receivers connected to the coupled array, which is something that has only recently been understood. The modeled and measured element receive patterns, array impedance matrix, signal and noise correlation matrices, and efficiencies and sensitivities of the PAF are compared and promising levels of agreement are shown. Modeled sensitivity is 30 to 46% larger than measured.

Presented herein is the design and construction process in the expansion of BYU's seven-element experimental platform to a nineteen-element platform for phased array feed experiments. The nineteen-element system was deployed at the National Radio Astronomy Observatory (NRAO) in Green Bank West Virginia for use on the Green Bank 20-Meter Telescope. Numerical simulations were performed to determine how sensitivity was affected by electronic beam steering and offset of the phased array feed (PAF) relative to the focal plane of the reflector. These simulated results were then compared to experimental data.

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.

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.

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