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.

RF receiver improvements in size, weight, power, and sensitivity are constant goals in the wireless communications community. The combination of phased array antenna systems with high speed analog to digital converters helps engineers meet these goals, because many of the analog components and tasks found in a traditional receive chain are moved into the digital domain. Although the hard work of signal reception is moved into digital signal processing, digital receivers rely on a high performance analog front end to properly condition a signal before analog to digital conversion. In this thesis, two RF front ends are developed for direct sampling L-band phased array receiver applications, which comprise the two main chapters of this document. Both RF front ends are developed on low cost, quick turnaround time PCB materials. Results for system gain and noise figure are presented for each front end. First, the development of an L-band analog front end for a direct sampling GPS phased array receiver is described, with particular attention to gain and noise figure in context of the full system link budget. The RF front end for the GPS phased array receiver meets design expectations by achieving a system gain of 65 dB and a system noise figure of 1.5 dB at the GPS L1 frequency. Second, the redesign and improvement of the Advanced L-band Phased Array Camera (ALPACA) RF over fiber transmitter is documented. New mechanical and electrical design requirements were brought on from the change of target observatory from the collapsed Arecibo obervatory in Puerto Rico, to the Greenbank Observatory in Greenbank, West Virginia. The ALPACA RF over fiber signal transport system with the redesigned transmitter reaches the design expectation of a system noise temperature contribution less than 1 K. Average gain of the RF over fiber system is 49 dB, gain differences between channels are less than 2 dB, and isolation between channels is better than 35 dB. Under optimal conditions, the noise figure of the RF over fiber link is 2.4 dB (213.3 K), which allows for up to 11 dB of attenuation to be added to any given transmit channel to level the gain across all 138 ALPACA channels.

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.

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