The Advanced L-Band Phased Array Feed for Astronomy (ALPACA) implements a two-stage “zoom” spectrom-eter to support multiple scientific modes. The first stage coarse spectrometer must be oversampled to avoid spectral degradation near band edges in the second stage fine spectrometer outputs used for HI mode observations. For pulsar studies, however, preliminary results show that using oversampled data may cause a loss of sensitivity in the parameter estimation used by the pulsar search algorithm. To overcome the sensitivity loss, we will implement a resampler following the coarse filterbank to provide critically sampled data when ALPACA is in pulsar search mode.

For wide-field astronomical phased array feeds, accurate beamformer calibration is required. Temperature variations and other environmental factors cause drifts in the phase and amplitude responses of the analog front end and RF- over-fiber signal transport system. To correct for these drifts and eliminate gain reductions and pattern drift in the formed beams, we have developed a distributed noise reference system that allows phase and amplitude recalibration. To validate the system, we use the reference system to correct the phase in a signal transport channel for the Advanced L-band Phased Array Camera for Astronomy (ALPACA) with a length of fiber inserted to mimic phase drifts.

A hardware and software pipeline is created to perform wideband interference cancellation through real-time beamforming.

Wideband beamforming and interference cancellation for phased array antennas requires advances in signal processing algorithms, software, and specialized hardware platforms. A high-throughput array receiver has been developed that enables communication in radio frequency interference-rich environments with field programmable gate array (FPGA)-based frequency channelization and packetization. In this study, a real-time interference mitigation algorithm was implemented on graphics processing units (GPUs) contained in the data pipeline. The key contribution is a hardware and software pipeline for subchannelized wideband array signal processing with 150 MHz instantaneous bandwidth and interference cancellation with a heterogeneous, distributed, and scaleable digital signal processing (DSP) architecture that achieves 30 dB interferer cancellation null depth in real time with a moving interference source.

To optimize the design of a high-sensitivity receiver, it is valuable to be able to assign noise budget contributions to various parts of the system. The system noise and aperture efficiency can be characterized using the antenna Y-factor method, which has been added recently to the IEEE Recommended Practice for Antenna Measurements, Std 149-2021. We extend the antenna Y-factor method by showing that it can be used to measure the noise figure of an active antenna and receiver system. With an additional measurement of the receiver noise, the antenna radiation efficiency can be determined. We demonstrate the extended antenna Y-factor method experimentally at X-band for antennas under test, including a horn with near 100% efficiency, microstrip patch antenna with efficiency near 80%, and a patch antenna array with 40% nominal efficiency.

The Advanced L-band Phased Array Camera for Astronomy (ALPACA) [2] is a cryogenic astronomical imaging phased array in development at Cornell University, Brigham Young University, for the Green Bank

The Advanced L-band Phased Array Camera for Astronomy (ALPACA) is a 69-element, fully cryogenic, phased array feed operating from 1.3-1.7 GHz proposed to be deployed at the prime focus of the 100-m Green Bank Telescope. Here we report on the progress towards assembling the front-end including a large RF-transparent vacuum window, the receiving elements, and several solutions we have deployed to significantly reduce the complexity of scaling the number of elements in an array. All the cryogenic low-noise amplifiers (LNAs) have been thermally cycled and rigorously tested. LNA bias and readout is shared on multi-channel flexible striplines that route from outside the cryostat through a vacuum interface and terminate at the cold stage where the antenna elements are deployed. ALPACA will act as a ‘Radio Camera’ by digitally forming 40 simultaneous dual polarization beams enabling large surveys for various radio astronomical applications.

After the catastrophic failure of the Arecibo Tele-scope on Dec. 1, 2020, the intended host telescope for the 69-element wide-field phased array feed ALPACA instrument was lost. Design of the RF -over-fiber (RFoF) signal transport link to the FPGA/GPU digital beamformer back end was revisited to accommodate the physical and operating requirements of a new host telescope. The equivalent noise temperature of the link must be below 850 K in order for signal transport to contribute no more than 1 K to the target system noise temperature performance of 27 K for the instrument. We present progress of the new design and report on its performance.

The Advanced L band Phased Array Camera for Arecibo (ALPACA) will rely on RF-over-fiber signal transport and hybrid FPGA/GPU signal processing hardware for calibration, beamforming, and imaging. We report on signal transport system development, phase and gain stability requirements, and array signal processing algorithm development.

For wideband phased array beamforming, multiport high throughput data acquisition and real time processing systems are required. This paper provides an overview of the development of a phased array receiver system for naval communications. This broadband heterogeneous system enables communication in hostile radio frequency interference (RFI)-rich environments with the aid of a real-time RFI mitigation algorithm currently implemented on graphics processing units (GPUs). The algorithm will be compatible with other phased array and phased array feed (PAF) receiver systems and will enable RFI mitigation in other applications such as radio astronomy. The system will be capable of receiving data from multiple transmitters and employs FPGAs and HPCs with integrated GPUs and FPGAs to process 150 MHz instantaneous bandwidth. This is the first system that we are aware of to demonstrate wideband, real-time RFI cancellation with a heterogeneous, distributed DSP architecture.

Brigham Young University (BYU), in collaboration with Cornell University, is developing the Advanced Cryogenic L-band Phased Array Camera for Arecibo (ALPACA) as a user provided facility instrument on the Arecibo 305 m radio telescope. This instrument will consist of a fully cryogenic 69-element phased array feed (PAF) and real-time digital beamformer back end capable of producing 40 simultaneous dual polarized beams with approximately 305 MHz of instantaneous bandwidth at 1.4 GHz. The target design goal is to operate with a system noise temperature of 25 K. We report on simulation results and a preliminary overview of the design and progress of the instrument's development.

Radio frequency interference (RFI) is rapidly becoming a major issue for many applications. It is especially problematic for radio astronomy, where signal-to-noise ratios (SNRs) are less than unity. Antenna array systems such as phased array feeds (PAFs) and interferometric imaging arrays are able to cancel RFI through adaptive projection-based spatial notch filtering techniques. Current methods for formulating these projection operators suffer from an unfortunate trade-off. They must sacrifice integration time when calculating the sample spatial correlation matrix in order to track RFI motion, but this consequently increases sample estimation error and reduces null depth. In this work, we propose a new way to process spatial correlation matrices to form a broad null that reliably cancels moving RFI without increasing sample estimation error due to insufficient integration. Additionally, when assisted by an RFI-tracking auxiliary antenna, this approach also reduces the total data rate coming out of a spatial correlator, thus making broad-null-based RFI cancelation more computationally efficient and practical for real-time active array-based RFI mitigation systems.

The White Paper describes Arecibo Observatory's plan for the next generation of upgrades to the Arecibo telescope in order to keep this national facility in the forefront of research in radio astronomy while maintaining its dominance in radar studies of near-Earth asteroids, planets and satellites.

ACKNOWLEDGMENTS I wish,to express,my gratitude,to Dr. Donald,Gustafson,for,his assistance,in the,statement,and,solution,of the,problems,presented,in this,thesis,and,his,guidance,in the,preparation,of the,manuscript. I wish,to thank,the,Learning,Center,of Texas,Instruments,Incorporated for,having,initiated,the,Master,Degree,program,under,which,I pursued the,graduate,studies,at Texas,Tech,University. 11 CONTENTS

Discover a modern approach to the analysis, modeling and design of high sensitivity phased arrays. Network theory, numerical methods and computational electromagnetic simulation techniques are uniquely combined to enable full system analysis and design optimization. Beamforming and array signal processing theory are integrated into the treatment from the start. Digital signal processing methods such as polyphase filtering and RFI mitigation are described, along with technologies for real-time hardware implementation. Key concepts from interferometric imaging used in radio telescopes are also considered. A basic development of theory and modeling techniques is accompanied by problem sets that guide readers in developing modeling codes that retain the simplicity of the classical array factor method while incorporating mutual coupling effects and interactions between elements. Combining current research trends with pedagogical material suitable for a first-year graduate course, this is an invaluable resource for students, teachers, researchers, and practicing RF/microwave and antenna design engineers.

A new 1.4 GHz, 19-element, dual-polarization, cryogenic phased-array feed (PAF) radio astronomy receiver has been developed for the Robert C. Byrd Green Bank Telescope (GBT) as part of the Focal L-band Array for the GBT (FLAG) project. Commissioning observations of calibrator radio sources show that this receiver has the lowest reported beam-formed system temperature (T-sys) normalized by aperture efficiency (eta) of any phased-array receiver to date. The measured T-sys/eta is 25.4 +/- 2.5. K near 1350 MHz for the boresight beam, which is comparable to the performance of the current 1.4 GHz cryogenic single-feed receiver on the GBT. The degradation in T-sys/eta at similar to 4'. (required for Nyquist sampling) and similar to 8' offsets from the boresight is, respectively, similar to 1% and similar to 20% of the boresight value. The survey speed of the PAF with seven formed beams is larger by a factor between 2.1 and 7 compared to a single-beam system, depending on the observing application. The measured performance, both in frequency and offset from the boresight, qualitatively agrees with predictions from a rigorous electromagnetic model of the PAF. The astronomical utility of the receiver is demonstrated by observations of the pulsar B0329+54 and an extended H II region, the Rosette Nebula. The enhanced survey speed with the new PAF receiver will enable the GBT to carry out exciting new science, such as more efficient observations of diffuse, extended neutral hydrogen emission from galactic inflows and searches for fast radio bursts.