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 development of phased array antenna systems requires considerable resources and time. Due to this constraint, the Naval Air Command (NAVAIR) needs a phased array that can be physically reconfigured to meet the demands of multiple missions without added development time or cost. This work develops and demonstrates a solution to this problem by implementing an adaptive calibration approach to the development of electronically steerable antennas (ESAs). In contrast to previous analog adaptive beamformer systems, this system allows for an arbitrary antenna configuration with a variable number of antenna elements and locations. A simulation model of arbitrary phased array configurations was developed to test the beamformer calibration algorithm and was used to show practical tile locations. To demonstrate this approach, four 4x4 ULA phased array antenna tiles were built and tested together in various configurations to show the viability of developing a physically reconfigurable phased array system.

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An aeroacoustic study was conducted on a 26%-scale Boeing 777 main landing gear in the Virginia Tech (VT) Anechoic Stability Wind Tunnel. The VT Anechoic Stability Wind Tunnel allowed noise measurements to be carried out using both a 63-elements microphone phased array and a linear array of 15 microphones. The noise sources were identified from the flyover view under various flow speeds and the phased array positioned in both the near and far-field. The directivity pattern of the landing gear was determined using the linear array of microphones. The effectiveness of 4 passive noise control devices was evaluated. The 26%-scale model tested was a faithful reproduction of the full-scale landing gear and included most of the full-scale details with accuracy down to 3 mm. The same landing gear model was previously tested in the original hard-walled configuration of the VT tunnel with the same phased array mounted on the wall of the test section, i.e. near-field position. Thus, the new anechoic configuration of the VT wind tunnel offered a unique opportunity to directly compare, using the same gear model and phased array instrumentation, data collected in hard-walled and semi-anechoic test sections. The main objectives of the present work were (i) to evaluate the validity of conducting aeroacoustic studies in non-acoustically treated, hard-walled wind tunnels, (ii) to test the effectiveness of various streamlining devices (passive noise control) at different flyover locations, and (iii) to assess if phased array measurements can be used to estimate noise reduction. As expected, the results from this work show that a reduction of the background noise (e.g. anechoic configuration) leads to significantly cleaner beamforming maps and allows one to locate noise sources that would not be identified otherwise. By using the integrated spectra for the baseline landing gear, it was found that in the hard-walled test section the levels of the landing gear noise were overestimated. Phased array measurements in the near and far-field positions were also compared in the anechoic configuration. The results showed that straight under the gear, near-field measurements located only the lower-truck noise sources, i.e. noise components located behind the truck were shielded. It was thus demonstrated that near-field, phased-array measurements of the landing gear noise straight under the gear are not suitable. The array was also placed in the far-field, on the rear-arc of the landing gear. From this position, other noise sources such as the strut could be identified. This result demonstrated that noise from the landing gear on the flyover path cannot be characterized by only taking phased array measurement right under the gear. The noise reduction potential of various streamlining devices was estimated from phased array measurements (by integrating the beamforming maps) and using the linear array of individually calibrated microphones. Comparison of the two approaches showed that the reductions estimated from the phased array and a single microphone were in good agreement in the far-field. However, it was found that in the near-field, straight under the gear, phased array measurements greatly overestimate the attenuation. / Master of Science

Modern radio astronomy’s demand for high sensitivity and wide fields of view is met through innovations that reduce receiver system noise temperatures and integrate technology supporting parallel processing and larger instantaneous bandwidths. The advanced L-band phased array camera for astronomy (ALPACA) is a fully cryogenic 69 dual-polarized dipole PAF and digital beamformer back end for the Green Bank Telescope. This instrument will form 40 dual-polarized beams yielding a 0.35 sq. deg field of view on the sky with a 305.2 MHz processing bandwidth. The target system noise temperature is 27 K. A structured technique to map critically sampled and oversampled polyphase filter banks (PFBs) onto a systolic array for implementation on a field programmable gate array (FPGA) is shown. This method provides unique insights into the operation of these algorithms. A case study for an oversampled PFB operating at 666.67 Msps shows that these designs effectively utilize FPGA resources, maintain high-throughput, and are flexible solutions for varied application requirements. A new class of FPGA, the Radio Frequency System-on-Chip (RFSoC), is integrated as a full-functioning software-defined hardware platform in an open-source signal processing toolchain. This provides astronomers with essential hardware for contemporary scientific research. The demonstration for an experimental technique for measuring antenna radiation efficiency using the antenna Y factor method is presented. The noise contribution of the ALPACA dipole when operating at cryogenic temperatures is estimated. Our findings show that the antenna is expected to contribute less than 1 K to the instrument’s overall system noise temperature. Research contributions of this work are: the integration of new high-performance digital hardware in radio astronomical PAF digital back ends, an open-source RFSoC signal processing development toolchain, an oversampled PFB using an FPAG-based systolic array design, and estimating the cryogenic noise temperature of an ALPACA dipole from its radiation efficiency.

The complexity of vehicular communication and radar sensing becomes increasingly complex with the growing demand for advanced driver-assistant systems in the automotive industry. Researchers are currently looking into combining communication and sensing by utilizing traditional communication waveforms in the mmWave radar bands to mitigate congestion and inter-radar interference. This thesis investigates a local-oscillator (LO) phase-shifting architecture to simplify the implementation of D-band (110–170 GHz) phased arrays for such applications. The constructed signal chain includes four 8–12-GHz voltage-controlled analog phase shifters, each mounted on the LO feed of a quadrature subharmonic upconverter, and a four-channel slot antenna. Through careful calibration of the analog control voltages, the 100-MHz baseband feed, and the LO distribution, antenna measurements in an anechoic chamber resulted in a beambook with antenna diagrams at seven angles from −30° to +30°. The gain was between 10.78 dB and 12.80 dB relative to the gain of one element, and the sidelobe levels were less than 8.9 dB. / Fordononsindustrins ökade efterfrågan på avancerade assistansystem gör framtidens kommunikation och radaravkänning allt mer komplex. Forskare undersöker just nu möjligheten att integrera kommunikation och radar genom att använda traditionella vågformer på millimetervågsfrekvenser för att förhindra nätverksträngsel och interferens mellan närliggande sensorer. Detta examensarbete undersöker möjligheten att fasstyra en radarantenn genom att skifta fasen på sändarens lokaloscillator (LO) och på så sätt förenkla konstruktionen av fasade gruppantenner på D-bandet (110–170 GHz). Signalkedjan bestod av fyra spänningsstyrda 8–12 GHz-fasskiftare, var och en monterade på LO-matningen till en subharmonisk mixer, samt en fyrkanals slitsantenn. Genom noggrann kalibrering av kontrollspänningar, 100 MHz-basbandsmatning och LO-distribution kunde antennmätningar i en ekofri kammare påvisa de önskade antenndiagramen för sju vinklar mellan −30° och +30°. Förstärkningen i förhållande till ett antennelement var mellan 10.78 dB och 12.80 dB och sidlobsnivåerna var lägre än 8.9 dB.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / This paper describes the Flexible Telemetry Transceiver (FNT)-a modular, scalable, standards-based, software configurable, microwave wireless telemetry network transceiver. The FNT enables flexible, high-rate, long-range, duplex, network services across multipoint to multipoint wireless channel.

The delivery of tunable millimetre-wave components at 60GHz is of research and development interests with the advent of 5G era. Among applications such as high-data-rate wireless communications, high-precision automotive radars and hand-gesture sensing, variable phase shifters are vital components for antenna arrays to steer an electromagnetic beam without mechanical movement. However, present microwave technology has limited scope in meeting more and more stringent requirements in wavefront phase control and device performance for those cutting-edge applications in the millimetre-wavelength range. Although some existing microwave switchable techniques (such as RF MEMS and solid-state p-i-n diodes) can offer ultra-fast speed for phase modulation, their binary beam-steering nature is resolution-limited and thereby degrades the beam-scanning performance. In response to this, continuously-tunable phase shifting can be realised by using tunable dielectric materials such as ferroelectric BST and liquid crystals (LCs). BST thin films can offer relatively fast switching and modest tunability. However, the increased dielectric loss beyond 10GHz impedes their implementation for higher frequency applications. By comparison, liquid crystals (LCs) have drawn attention in recent years because of their continuous tunability as well as low losses especially at millimetre-wavebands. The principle of shifting the phase continuously is based on the shape anisotropy of LC molecules for variable polarizabilities and hence tunable dielectric constants, which allows wave speed to be controlled with ease by a low-frequency field of only up to 10V. However, LC-based tunable delay lines are not well established in the frequency regime of 60GHz-90GHz because of the limited status of LC microwave technology in which most of the LC based devices have been designed for below 40GHz. It is the aim of this PhD research to bridge the gap and address future societal needs based on our group's focus and experience in developing cutting-edge LC-based agile microwave components. In this work, a liquid crystal (LC) based 0-180˚continuously-variable phase shifter is developed with insertion loss less than -4.4dB and return loss below -15dB across a wide spectrum from 54GHz to 67GHz. The device is driven by a 0-10V AC bias and structured in a novel enclosed coplanar waveguide (ECPW) including an enclosed ground plate in the design, which significantly reduces the instability due to floating effects of the transmission line. This structure screens out interference and stray modes, allowing resonance-free quasi-TEM wave propagation up to 90GHz. The tunable ECPW is optimised by competing spatial volume distribution of the millimetre-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics and minimising the total of dielectric volumetric loss and metal surface loss for a fixed phase-tuning range. A variety of influences affecting the actual device performance are studied, experimented and optimised. Fabricated prototypes exhibit wideband low-loss performance and 0-π continuous tuning with low power consumptions and high linearity compared with the state-of-the-arts. Potentially, the ECPW-fed phased antenna array will be incorporated with advanced beam-forming algorithms to develop compact beam-steering systems of improved performances and targeted for ultra-high-data-rate wireless communications, inter-satellite communications, current road safety improvement, futuristic autonomous driving, and other smart devices such as the hand-gesture recognition.

Le projet Iseult-Inumac mené au sein d’un consortium franco-allemand vise à développer les techniques associées à l’imagerie par résonance magnétique à ultra haut champ, notamment à travers la construction d’un imageur à 11,7 teslas. La résolution accrue du nouvel imageur devrait apporter une meilleure compréhension du système nerveux et de ses dysfonctionnements pour aboutir à un dépistage plus précoce des pathologies telles que la maladie d’Alzheimer, les accidents vasculaires cérébraux ou les tumeurs.La principale difficulté technique du projet, en dehors de la construction de l’aimant statique, réside dans la capacité d’émettre une onde électromagnétique d’amplitude uniforme dans tout le cerveau du patient : problème de l’inhomogénéité de B1 (ou radiofréquence). Une solution proposée consiste à utiliser une antenne réseau à transmission parallèle et des séquences d’excitation IRM spécifiques dites de compensation.Cette thèse se concentre sur la conception des antennes réseaux à transmission parallèle pour l’IRM à 7 et 11,7 T. Un prototype à 8 canaux indépendants utilisant une technologie innovante de résonateurs linéaires est présentée pour l’IRM 7 T. Il a été conçu par la simulation numérique. Un protocole de validation a été développé pour la caractérisation et l’analyse des performances des antennes réseaux. Le succès de cette validation a permis de développer par la simulation une nouvelle antenne à 12 canaux et une stratégie de pilotage innovante permettant de n’utiliser que 8 chaînes de pilotage au lieu de 12. Enfin, la même méthodologie a été appliquée pour concevoir et prédire les performances d’une antenne réseau à 11,7 T. / The Iseult-Inumac project led by a franco-german consortium aims at developing the ultra-high field MRI technologies, especially with the building of an 11.7 tesla scanner. The high resolution of this new scanner may improve the understanding of human nervous system and its dysfunctions in order to detect pathologies like the Alzheimer disease, strokes or tumors earlier.The biggest technical difficulty, besides the building of the static magnet itself, lies in the emission of a uniform electromagnetic wave in the entire brain of the patient. It is usually referred as to B1 (or RF) inhomogeneity issues. A solution consists in using a phased array RF coil and specific MRI sequences for shimming in a parallel transmit approach.This thesis deals with the study of parallel transmit phased arrays RF coils for 7 T and 11.7 T MRI. An eight independent channels prototype-coil that uses a new planar strip array technology is described for 7 T MRI. It was designed based on numerical simulation. A validation methodology has been developed for characterization and performance analysis of transmit phased arrays. After a successful validation of this first prototype, a more efficient 12-channel coil and a new driving strategy that only requires 8 driving channels instead of 12 were designed. Finally, the same methodology was applied to a phased array RF coil for 11.7 T MRI.

Modern radar technology relies heavily on digital signal processing. As radar technology pushes the boundaries of miniaturization, computational systems must be developed to support the processing demand. One particular application for small radar technology is in modern drone systems. Many drone applications are currently inhibited by safety concerns of autonomous vehicles navigating shared airspace. Research in radar based Detect and Avoid (DAA) attempts to address these concerns by using radar to detect nearby aircraft and choosing an alternative flight path. Implementation of radar on small Unmanned Air Vehicles (UAV), however, requires a lightweight and power efficient design. Likewise, the radar processing system must also be small and efficient.This thesis presents the design of the processing system for a small Frequency Modulated Continuous Wave (FMCW) phased array radar. The radar and processing is designed to be light-weight and low-power in order to fly onboard a UAV less than 25 kg in weight. The radar algorithms for this design include a parallelized Fast Fourier Transform (FFT), cross correlation, and beamforming. Target detection algorithms are also implemented. All of the computation is performed in real-time on a Xilinx Zynq 7010 System on Chip (SoC) processor utilizing both FPGA and CPU resources.The radar system (excluding antennas) has dimensions of 2.25 x 4 x 1.5 in3, weighs 120 g, and consumes 8 W of power of which the processing system occupies 2.6 W. The processing system performs over 652 million arithmetic operations per second and is capable of performing the full processing in real-time. The radar has also been tested in several scenarios both airborne on small UAVs as well as on the ground. Small UAVs have been detected to ranges of 350 m and larger aircraft up to 800 m. This thesis will describe the radar design architecture, the custom designed radar hardware, the FPGA based processing implementations, and conclude with an evaluation of the system's effectiveness and performance.