The objective of this research is to understand the design and performance of state-of-the-art silicon-germanium (SiGe) BiCMOS high-frequency circuits for phased- array radar and wireless communication systems operating in extreme environment conditions. This work investigates the performance of RF circuits over a wide- temperature and exposure to a radiation intensive environment. The design and characterization of a fully integrated transmit/receive (T/R) module and integra- tion onto a multi-element antenna array is presented. In addition, individual circuit blocks are characterized in these extreme environments.

With the advancement in wireless communication, there has been a lot of overlap in the frequency spectrum used by different applications in the lower frequency band. Also there is an ever-increasing demand for high-speed wireless data transfer. Due to the aforementioned reasons, a lot of work is being done recently in the unlicensed 60GHz bandwidth due to the high data rates it can support. But it is tough to achieve long-range point-to-point transmission at this frequency due to the limited output power and high path losses. A phased array system is a viable solution at these mmWave frequencies to achieve highly directive long-range point-to-point communication. The objective of this research is the design and implementation of phase shifters, VCO and LNA for mmWave phased array system. In this work, active and passive quadrature generation schemes integrated with a vector modulator have been proposed that can be used to produce arbitrary phase shift with a deterministic resolution at the LO signal. Also, alternate IF and PLL based phase shifting schemes for a mmWave phased array system have been proposed. A complete design procedure from parasitic modeling of devices to verification of the design using EM simulations has been discussed in this work. The simulation results are compared with actual measurement results from the fabricated chip and the performance of the various circuits has been analyzed. Furthermore, the designs of VCO and low noise amplifier to be used in the mmWave phased array system are discussed here.

The work here presents a review of beam forming architectures. As an example, the author presents an 8x8 Butler Matrix passive beam forming network including the schematic, design/modeling, operation, and simulated results. The limiting factor in traditional beam formers has been the large size dictated by transmission line based couplers. By replacing these couplers with transformer-based couplers, the matrix size is reduced substantially allowing for on chip compact integration. In the example presented, the core area, including the antenna crossover, measures 0.82mm×0.39mm (0.48% the size of a branch line coupler at the same frequency). The simulated beam forming achieves a peak PNR of 17.1 dB and 15dB from 57 to 63GHz. At the 60GHz center frequency the average insertion loss is simulated to be 3.26dB. The 8x8 Butler Matrix feeds into an 8-element antenna array to show the array patterns with single beam and adjacent beam isolation.

The focus of this dissertation is on the development and circuit modeling of planar series-fed, linear- and circular-polarized microstrip aperture-coupled antennas and N-element arrays operating in C-band. These arrays were designed to be used as part of airborne or land-based frequency-hopped communication systems. One of the main objectives of this work was to maintain a constant beam angle over the frequency band of operation. In order to achieve constant beam pointing versus frequency, an anti-symmetric series-fed approach using lumped-element circuit models was developed. This series feed architecture also balances the power radiated by each element in the N-element arrays. The proposed series-fed approach was used in the development of four-element series-fed aperture-coupled arrays with 15% 10 dB impedance bandwidth centered at 5 GHz and a gain of 11.5 dB, to construct an omni-directional radiator. Omni-directional radiators with pattern frequency stability are desired in a multitude of applications; from defense in tactical communications, information gathering, and detection of signal of interest to being part of sensors in medical applications. A hexagonal assembly of six series-fed microstrip aperture-coupled four-element arrays was used to achieve the omni-directional radiation with 0.6 dB peak to peak difference across 360˚ broadside pattern and 0.6 dB gain variation at the specific azimuth angle across 15% impedance bandwidth. Given that each of these six arrays can be individually controlled, this configuration allows for individual pattern control and reconfiguration of the omni-directional pattern with increased gain at specific azimuth angles and the ability to form a directional pattern by employing a fewer number of arrays. Incorporating a beam-forming network or power distribution network is also possible. Wide 3 dB circular polarization (CP) bandwidth was achieved without external couplers and via only a single feed with a unique Z-slot aperture-coupled microstrip antenna. A single RHCP Z-slot aperture-coupled antenna has ∼10% CP and 10 dB impedance bandwidth. The series-fed network consisting of lumped elements, open-circuited stubs and transmission lines was subsequently developed to maintain more than 5% CP and 10% 10 dB impedance bandwidth in the series-fed four-element Z-slot aperture-coupled CP array that could also be used for-omni-directional radiation.

Silicon based on-chip optical phased arrays are an enabling technology to achieving agile and compact large angle beam steering. In this work, a single layer array is presented, and approaches to multilayer 3D photonic integration for achieving a 2D array are also discussed. Finally, two dimensional optical beam steering is achieved using both thermo-optic and wavelength tuning. Various structures are considered as an alternative to the conventionally used shallow etched surface gratings to achieve narrow beam widths in the far field along with low switching power. The corrugated waveguide interspersed with 2D photonic crystal for crosstalk suppression is presented as a novel structure for coupling to free space that can provide lithographically defined index contrast in a single fabrication step, along with the smallest beam widths presented to date, at 0.25°. In addition, a polysilicon overlay with an oxide etch stop layer on top of a silicon waveguide is also presented as a grating coupler that achieves narrow far field beam widths. With this structure, two dimensional steering of 20° X 15° is demonstrated with a 16 element optical phased array, with a beam width of 1.2° X 0.4° and maximum power consumption of 20mW per channel. / text

Η διδακτορική διατριβή αναφέρεται στην χρήση των πηνίων λήψης κατά την απεικόνση μαγνητικού συντονισμού. Στα πλαίσια της ερευνητικής εργασίας προσομοιώθηκε ένα σύστημα πηνίων φασικής συνάφειας 4 ορθογωνικών στοιχείων με διαστάσεις μικρότερες των συμβατικών πηνίων για την βελτίωση του σηματοθορυβικού λόγου στις εξετάσεις του ανθρώπινου προστάτη. Το σύστημα αυτό στη συνέχεια σχεδιάστηκε και υλοποιήθηκε χρησιμοποιώντας συγκεκριμένες τεχνικές αποσύζευξης των γειτονικών στοιχείων, συντονισμού στη συχνότητα Larmor, προσαρμογής του φορτίου στα 50 Ohm και ελέγχου διακοπής. Η τελική μορφή του πηνίου εφαρμόστηκε σε κλινικό μαγνητικό τομογράφο 1.5Τ, όπου πραγματοποιήθηκαν μετρήσεις σε ομοιώματα και σε μία μεσαίου μεγέθους ανθρώπινη πυελική περιοχή. Τα αποτελέσματα συγκρίθηκαν με εκείνα των συμβατικων πηνίων (flex 4-channel cardiac coil), ενώ οι in vivo εξετάσεις έδειξαν σημαντική βελτίωση στο τελικό σήμα της εικόνας όταν χρησιμοποιούμε περισσότερο εντοπισμένα παραθύρα απεικόνισης (FOV). / The doctoral thesis refers to the use of receiver coils during MR imaging experiments. We simulated a 4-channel phased array system of orthogonal elements with reduced size compare to the conventional coils in order to improve the signal-to-noise ratio in prostate MR imaging. That system was then designed and developed using particular decoupling, tuning, matching and switching techniques. The final design was tested clinically on a 1.5T MRI system using phantoms at first and then an average sized human pelvic region. The results were compared to those extracted from a conventional flex 4-channel cardiac coil, while the in vivo images showed considerable improvement in contrast when we used more localized field of views.

Ever growing demands for higher data rate and bandwidth are pushing extremely high data rate wireless applications to millimeter-wave band (30-300GHz), where sufficient bandwidth is available and high data rate wireless can be achieved without using complex modulation schemes. In addition to the communication applications, millimeter-wave band has enabled novel short range and long range radar sensors for automotive as well as high resolution imaging systems for medical and security. Small size, high gain antennas, unlicensed and worldwide availability of released bands for communication and a number of other applications are other advantages of the millimeter-wave band. The major obstacle for the wide deployment of commercial wireless and radar systems in this frequency range is the high cost and bulky nature of existing GaAs- and InP-based solutions. In recent years, with the rapid scaling and development of the silicon-based integrated circuit technologies such as CMOS and SiGe, low cost technologies have shown acceptable millimeter-wave performance, which can enable highly integrated millimeter-wave radio devices and reduce the cost significantly. Furthermore, at this range of frequencies, on-chip antenna becomes feasible and can be considered as an attractive solution that can further reduce the cost and complexity of the radio package. The propagation channel challenges for the realization of low cost and reliable silicon-based communication devices at millimeter-wave band are severe path loss as well as shadowing loss of human body. Silicon technology challenges are low-Q passive components, low breakdown voltage of active devices, and low efficiency of on-chip antennas. The main objective of this thesis is to investigate and to develop antenna and front-end for cost-effective silicon based millimeter-wave phased array radio architectures that can address above challenges for short range, high data rate wireless communication as well as radar applications. Although the proposed concepts and the results obtained in this research are general, as an important example, the application focus in this research is placed on the radio aspects of emerging 60 GHz communication system. For this particular but extremely important case, various aspects of the technology including standard, architecture, antenna options and indoor propagation channel at presence of a human body are studied. On-chip dielectric resonator antenna as a radiation efficiency improvement technique for an on-chip antenna on low resistivity silicon is presented, developed and proved by measurement. Radiation efficiency of about 50% was measured which is a significant improvement in the radiation efficiency of on-chip antennas. Also as a further step, integration of the proposed high efficiency antenna with an amplifier in transmit and receive configurations at 30 GHz is successfully demonstrated. For the implementation of a low cost millimeter-wave array antenna, miniaturized, and efficient antenna structures in a new integrated passive device technology using high resistivity silicon are designed and developed. Front-end circuit blocks such as variable gain LNA, continuous passive and active phase shifters are investigated, designed and developed for a 60GHz phased array radio in CMOS technology. Finally, two-element CMOS phased array front-ends based on passive and active phase shifting architectures are proposed, developed and compared.

Focused ultrasound combined with intravenously injected microbubbles is a promising non-invasive therapy capable of temporarily disrupting the blood-brain barrier for targeted drug delivery. Established in vivo experiments on rodent models combine focused ultrasound treatment with two-photon microscopy imaging to improve understanding of microvasculature response. A phased array, an advanced ultrasound therapy device, was successfully developed to improve pressure transmission in these experiments. An investigation of transducer sensitivity to setup equipment suggested modifications to setup procedures, for example recording objective position, may improve in situ pressure estimates. A ring array composed of 50 lateral mode elements, geometry determined by pressure field simulations, was successfully fabricated. Fibre optic hydrophone pressure field measurements confirmed the device had an appropriate focal size (0.7mm diameter x 4mm axial length) and reached therapeutic pressure levels (>0.5MPa). Ex vivo transcranial measurements demonstrated moderate focal correction and off-axis steering capabilities that may improve experimental throughput and target alignment.

Focused ultrasound combined with intravenously injected microbubbles is a promising non-invasive therapy capable of temporarily disrupting the blood-brain barrier for targeted drug delivery. Established in vivo experiments on rodent models combine focused ultrasound treatment with two-photon microscopy imaging to improve understanding of microvasculature response. A phased array, an advanced ultrasound therapy device, was successfully developed to improve pressure transmission in these experiments. An investigation of transducer sensitivity to setup equipment suggested modifications to setup procedures, for example recording objective position, may improve in situ pressure estimates. A ring array composed of 50 lateral mode elements, geometry determined by pressure field simulations, was successfully fabricated. Fibre optic hydrophone pressure field measurements confirmed the device had an appropriate focal size (0.7mm diameter x 4mm axial length) and reached therapeutic pressure levels (>0.5MPa). Ex vivo transcranial measurements demonstrated moderate focal correction and off-axis steering capabilities that may improve experimental throughput and target alignment.

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