International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The U.S. Army Redstone Technical Test Center (RTTC) uses telemetry as a vital part of its data acquisition and analysis for electromagnetic environmental effects developmental testing of U.S. Army weapon systems. Testing in an electromagnetic environment poses several unique challenges. These challenges have resulted in the development of highly customized telemetry and data acquisition systems. This paper discusses the design and integration of past and current telemetry needs to incorporate real-time or near real-time simulations or scene generations into the testing process.

International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California / High explosive radio telemetry (HERT) is a project that is being developed jointly by Los Alamos National Laboratory and AlliedSignal FM&T. The ultimate goal is to develop a small, modular telemetry system capable of high-speed detection of explosive events, with an accuracy on the order of 10 nanoseconds. The reliable telemetry of this data, from a high-speed missile trajectory, is a very challenging opportunity. All captured data must be transmitted in less than 20 microseconds of time duration. This requires a high bits/Hertz microwave telemetry modulation code to insure transmission of the data within the limited time interval available.

Το αντικείμενο της παρούσης διπλωματικής επικεντρώνεται στη σχεδίαση ανάπτυξη και μέτρηση κυκλώματος κάτω μεταλλάκτη (down converter) συχνότητας στην περιοχή 1 έως 6 GHz. Η αρχιτεκτονική περιλαμβάνει ενισχυτή χαμηλού θορύβου (LNA) κατανεμημένης τοπολογίας (distributed amplifier), μίκτη καθώς και ενισχυτές και φίλτρα στην ενδιάμεση συχνότητα. Ο σχεδιασμός συνοδεύεται από μετρήσεις όπου και διαπιστώνεται η σύγκλιση με τα αποτελέσματα εντατικών εξομοιώσεων. Κύρια εργαλεία του σχεδιασμού απετέλεσαν κυκλωματικοί και ηλεκτρομαγνητικοί εξομοιωτές. / The object of this thesis focuses on design development and measurement down converter circuit in the frequency range 1 to 6 GHz. The architecture includes low noise amplifier (LNA) Distributed topology (distributed amplifier), mixer and amplifiers and filters in intermediate frequency. The design is accompanied by measurements and found where the convergence of the results of intensive simulations. Main tools of design were kyklomatikoi and electromagnetic simulators.

This dissertation explores the realm of high-accuracy localization through the utilization of ranging-based techniques, encompassing a spectrum of signals ranging from low-frequency ultrasound acoustic signals to more intricate high-frequency signals like Wireless Fidelity (Wi-Fi) IEEE 802.11az, 5G New Radio (NR), and 6G. Moreover, another contribution is the conception of a novel timing mechanism and synchronization protocol grounded in tunable quantum photonic oscillators. In general, our primary focus is to facilitate precise indoor localization, where conventional GPS signals are notably absent. To showcase the significance of this innovation, we present two vital use cases at the forefront: drone localization and metaverse user positioning. In the context of indoor drone localization, the spectrum of applications ranges from recreational enthusiasts to critical missions requiring pinpoint accuracy. At the hobbyist level, drones can autonomously navigate intricate indoor courses, enriching the recreational experience. As a finer illustration of a hobbyist application, consider the case of ``follow me drones". These specialized drones are tailored for indoor photography and videography, demanding an exceptionally accurate autonomous flight capability. This precision is essential to ensure the drone can consistently track and capture its designated subject, even as it moves within the confined indoor environment. Moving on from hobby use cases, the technology extends its profound impact to more crucial scenarios, such as search and rescue operations within confined spaces. The ability of drones to localize with high precision enhances their autonomy, allowing them to maneuver seamlessly, even in environments where human intervention proves challenging. Furthermore, the technology holds the potential to revolutionize the metaverse. Within the metaverse, where augmented and virtual realities converge, the importance of high-accuracy localization is amplified. Immersive experiences like Augmented/Virtual/Mixed Reality (AR/VR/MR) gaming rely heavily on precise user positioning to create seamless interactions between digital and physical environments. In entertainment, this innovation sparks innovation in narrative design, enhancing user engagement by aligning virtual elements with real-world surroundings. Beyond entertainment, applications extend to areas like telemedicine, enabling remote medical procedures with virtual guidance that matches physical reality. In light of all these examples, the imperative for an advanced high-accuracy localization system has become increasingly pronounced. The core objective of this dissertation is to address this pressing need by engineering systems endowed with exceptional precision in localization. Among the array of potential techniques suitable for GPS-absent scenarios, we have elected to focus on ranging-based methods. Specifically, our methodologies are built upon the fundamental principles of time of arrival, time difference of arrival, and time of flight measurements. In essence, each of our devised systems harnesses the capabilities of beacons such as ultrasound acoustic sensors, 5G femtocells, or Wi-Fi access points, which function as the pivotal positioning nodes. Through the application of trilateration techniques, based on the calculated distances between these positioning nodes and the integrated sensors on the drone or metaverse user side, we facilitate robust three-dimensional localization. This strategic approach empowers us to realize our ambition of creating localization systems that not only compensate for the absence of GPS signals but also deliver unparalleled accuracy and reliability in complex and dynamic indoor environments. A significant challenge that we confronted during our research pertained to the disparity in z-axis localization performance compared to that of the x-y plane. This nuanced yet pivotal concern often remains overlooked in much of the prevailing state-of-the-art literature, which predominantly emphasizes two-dimensional localization methodologies. Given the demanding context of our work, where drones and metaverse users navigate dynamically across all three dimensions, the imperative for three-dimensional localization became evident. To address this, we embarked on a comprehensive analysis, encompassing mathematical derivations of error bounds for our proposed localization systems. Our investigations unveiled that localization errors trace their origins to two distinct sources: errors induced by ranging-based factors and errors stemming from geometric considerations. The former category is chiefly influenced by factors encompassing the quality of measurement devices, channel quality in which the signal communication between the sensor on the user and the positioning nodes takes place, environmental noise, multipath interference, and more. In contrast, the latter category, involving geometry-induced errors, arises primarily from the spatial configuration of the positioning nodes relative to the user. Throughout our journey, we dedicated efforts to mitigate both sources of error, ensuring the robustness of our system against diverse error origins. Our approach entails a two-fold strategy for each proposed localization system. Firstly, we introduce innovative techniques such as Frequency-Hopping Spread Spectrum (FHSS) and Frequency-Hopping Code Division Multiple Access (FH-CDMA) and incorporate devices such as Reconfigurable Intelligent Surfaces (RIS) and photonic oscillators to fortify the system against errors stemming from ranging-related factors. Secondly, we devised novel evolutionary-based optimization algorithms, adept at addressing the complex NP-Hard challenge of optimal positioning node placement. This strategic placement mitigates the impact of geometry-induced errors on localization accuracy across the entire environmental space. By meticulously addressing both these sources of error, our localization systems stand as a testament to comprehensive robustness and accuracy. Our methodologies not only extend the frontiers of three-dimensional localization but also equip the systems to navigate the intricacies of indoor environments with precision and reliability, effectively fulfilling the evolving demands of drone navigation and metaverse user interaction. / Doctor of Philosophy / In this dissertation, we first explore some promising substitutes for the Global Positioning System (GPS) for the autonomous navigation of drones and metaverse user positioning in indoor spaces. Then, we will make the scope of research more comprehensive and try to explore substitutes to GPS for autonomous navigation of drones in general, both in indoor environments and outdoors. For the first part, we make our small indoor GPS. Similar to GPS, in our system, a receiver onboard the drone or the metaverse user can receive signals from our small semi-satellites in the room, and with that, it can localize itself. The idea is very similar to how the well-known GPS works, with some modifications. Unlike the GPS, we are using acoustic ultrasound signals or some RF signal based on 5G or Wi-Fi for transmission. Also, we have more freedom compared to GPS because, in GPS, they have to transmit signals from far ahead distances, whereas, in our scenario, it is just a room in which we put all of our semi-satellite transmitters. Moreover, we can put them anywhere we want in the room. This is, in fact important, because the positions of these semi-satellites have a huge effect on the accuracy of our system. Also, we can decide how many of them we need to cover every point in the room and not have any blind spots. We propose our novel techniques for finding the optimal placement to improve localization accuracy. In GPS, they propose a technique that is suitable for the case of those satellites and their distance to the targets. Similarly, we offer our novel techniques to have a robust transmission against noise and other factors and guarantee a localization scheme with high accuracy. All being said, our proposed system for indoor localization of drones and metaverse users in three dimensions has considered all the possible sources of error and proposed solutions to conquer them; hence a robust system with high accuracy in three-dimensional space.

Exploring RF models for an integrated power electronics module (IPEM) is crucial to analyzing and predicting its EMI performance. This thesis deals with the parasitics extraction approach for an active IPEM in a frequency range of 1MHz through 30MHz. Based on the classic electromagnetic field theory, the calculating equations of DC and AC parameters for a 3D conducting structure are derived. The influence of skin effect and proximity effect on AC resistances and inductances is also investigated at high frequencies. To investigate RF models and EMI performance of the IPEM, a 1kW 1MHz series resonant DC-DC converter (SRC) is designed and fabricated in this work. For extracting the stray parameters of the built IPEM, two main software simulation tools ¡ª Maxwell Quick 3D Parameter Extractor (Maxwell Q3D) and Maxwell 3D Field Simulator (Maxwell 3D), prevailing electromagnetic simulation products from Ansoft Corporation, are introduced in this study. By trading off between the numerical accuracy and computational economy (CPU time and consumption of memory size), Maxwell Q3D is chosen in this work to extract the parameters for the full bridge IPEM structure. The step-by-step procedure of using Maxwell Q3D is presented from pre-processing the 3D IPEM structure to post-processing the solutions, and exporting equivalent circuit for PSpice simulations as well. RF modeling of power MOSFETs is briefly introduced. In order to verify extracted parameters, in-circuit impedance measurements for the IPEM using Agilent 4294A Impedance Analyzer together with Agilent 42941A probe are then followed. Measured results basically verify the extracted data, while the discrepancy between measured results and simulated results is also analyzed. / Master of Science

Due to the demand for low-cost, small-form factor and large-scale integration of system-on-chip wireless transceivers, the image-reject, zero-IF and low-IF receiver architectures have become the main topologies used in mainstream wireless communication systems. Consequently, signal sources with quadrature phase outputs [quadrature oscillators (QOs)] are therefore essential, and their phase noise, driving capability, tuning range, oscillation frequency, and power consumption have a major impact on the overall receiver performance. Additionally, it is required that the QO synthesize precise I/Q waveforms across the signal bandwidth over process, voltage, and temperature variations for adequate image-rejection and signal modulation/demodulation. While the use of symmetrical layout and large inter-digitated devices minimize both systematic and random mismatches, this solution alone may not succeed in achieving the stringent performance requirements dictated by modern wireless standards particularly as the technology scales into the sub-100nm regime, necessitating both phase and gain calibration of the mismatched I/Q channels post-fabrication. Given the necessity for precise RF quadrature signal synthesis, the goal of this work is to investigate low-power low-phase-noise quadrature oscillator (QVCO) topologies with an integrated phase calibration feature. The first part of this work focuses on the analysis and modeling of cross-coupled LC QVCOs. The analysis focuses on understanding the oscillator basic performance characteristics, design trade-offs, phase-noise performance, effect of including phase shift in the coupling paths, and on examining the quadrature accuracy in presence of process variations. New design parameters and circuit insight are developed and a generalized first order linear model and a one-port model are proposed. Particularly, we introduce the concept of an effective core and coupling transconductances to explain various oscillator properties. Additionally, a new incremental circuit element — the quadrature resistance — is introduced to evaluate the effect of coupling on the open-loop quality factor and hence on the oscillator phase noise performance. Mechanisms affecting the mode selectivity are identified and modeled. A qualitative and quantitative study of the effect of mismatch on the phase imbalance and amplitude error is presented. Particularly, closed-form intuitive expressions of the phase imbalance and amplitude error are derived and verified via circuit simulation. Based on our understanding of the various mechanisms affecting the quadrature accuracy, the second part of this work introduces a very efficient quadrature phase calibration technique based on the disconnected-source parallel-coupled LC QVCO topology. The phase-tunable LC QVCO (PT-QVCO) achieves an ultra-wide I/Q phase tuning range without affecting the relative amplitude error or consuming additional power or chip area. Additionally, in restoring the phase balance, it is observed that the proposed method restores the phase noise performance to its optimal value which presents a potential advantage over classical calibration techniques. Time domain measurements performed on a 5 GHz prototype show that I/Q signals with phase error up to ~±30°, beyond which the VCO cores are unlocked, can be driven to perfect quadrature phase. The PT-QVCO can be tuned from 3.87-4.45 GHz at the negative mode and 4.4-5.4 GHz at the positive mode, a total of ~1.5 GHz. The fabricated circuit including pad structures occupies an area of 1.1x0.7 mm² and drains 18mW (excluding buffer circuits) from a 1.8 V supply voltage. The third part of this work introduces a new low-power, low-phase-noise super harmonic injection-coupled LC QVCO (IC-QVCO) topology. Analysis of the waveform accuracy reveals an inverse dependence of the quadrature error on the tank quality factor thus allowing circuit optimization for both low phase noise and precise quadrature synthesis. Additionally, a tunable tail filter (TTF) is incorporated to calibrate the residual quadrature imbalance in presence of a 3-σ variation in the device parameters. An X-band IC-QVCO prototype with a TTF implemented in a 0.18μm RF CMOS process, achieves a measured phase noise figure-of-merit ranging from 177.3 to 182.6 dBc/Hz along the 9.0 to 9.6 GHz frequency tuning range while dissipating only 9mW from the 1.8V supply. The TTF reduces both the 1/f² and 1/f³ phase noise and calibrates the residual phase error within ±11° post-fabrication without affecting the relative amplitude error or the phase noise performance. The circuit performance compares favorably with recently published work. In the fourth part of this work, we explore the implementation of LC QVCOs as potential I/Q sources at millimeter-wave (MMW) frequencies. Among the several design challenges that emerge as the oscillator frequency is scaled into the MMW band, precise quadrature synthesis and adequate frequency tuning range are among the hardest to achieve. After describing the limitation of using an MOS varactor and a digitally controlled switch capacitor array for frequency tuning, we propose an alternative frequency tuning technique based on the fundamental operation of LC QVCOs. The off-resonance operation, which is defined by the coupling network, suggests varying the coupling current to achieve frequency tuning. In essence, by modifying the bias current of the coupling transistors (G_Mc-tuning), a wide and linear frequency tuning range can be achieved. Extensive simulation results of a 60 GHz prototype, implemented in a 90 nm commercial RF CMOS process, demonstrates a 5 GHz of frequency tuning range (57.5 GHz → 62.5 GHz), a tuning sensitivity of 1GHz/mA, and a 4dB improvement in the phase noise compared to a varactor solution. Finally, the Appendix includes recent research work on the analysis and design of g<sbu>m</sub>-boosted common-gate low-noise amplifiers (CG-LNAs). While this topic seems to diverge from the main theme of the dissertation, we believe that the comprehensive analysis and the originality of the circuit design introduced in this work are worth acknowledging. / Ph.D. / While resting in bed due to illness, the Dutch scientist Christiaan Huygens keenly observed that the pendulums of two clocks hanging on the wall moved synchronously when the clocks were hung close to each other. He concluded that these two oscillatory systems were forced to move in unison by virtue of mechanical coupling through the wall. In essence, each pendulum injected mechanical vibrations into the wall that was strong enough to lock the adjacent pendulum into synchronous motion. Injection locking of oscillatory systems plays a critical role in communication systems ranging from frequency division, to generating clocks (oscillators) with finer phase separation, to the synthesis of orthogonal (quadrature) clocks. All communication systems have the same basic form. Firstly, there will some type of an information or data source which can be a keyboard or a microphone in a smartphone. The source is connected to a receiver by some sort of a channel. In wireless systems, the channel is the air medium. Moreover, to comply with the FCC and 3GPP requirements, data can only be transmitted wirelessly within a predefined set of frequencies and with stringent emission requirements to avoid interference with other wireless systems. These frequencies are generated by high fidelity clock sources, also known as oscillators. Consider a group of people sharing the same room and hence the same channel want to share information. Without regulating the “loudness” of each communicating ensemble, the quality of communication can be severely impaired. Moreover, it is to be expected that information can be shared more efficiently if each pair is allocated non-overlapping timeslots – speak when others are quiet. Called time orthogonality, all wireless systems require precise orthogonal (quadrature) clock sources to improve the communication efficiency. The precision of quadrature clocks is determined by the amplitude and phase accuracy. This dissertation takes a deep dive into the analysis and implementation of high accuracy quadrature (I/Q) clock sources using the concept of injection locking. These I/Q clocks or oscillators, also known as quadrature voltage controlled oscillators (QVCOs), have gained enormous popularity in the last decade. The first part of this work focuses on the analysis and modeling of QVCOs. The analysis focuses on understanding the oscillator basic performance characteristics, and on examining the quadrature accuracy in presence of process variations. New design parameters and circuit insight are developed and a generalized first order linear model and a one-port model are proposed. A qualitative and quantitative study of the effect of mismatch on the phase imbalance and amplitude error is presented. Particularly, closed-form intuitive expressions of the phase imbalance and amplitude error are derived and verified via circuit simulation. Based on our understanding of the various mechanisms affecting the quadrature accuracy, the second part of this work introduces a very efficient quadrature phase calibration technique based The phase-tunable QVCO (PT-QVCO) achieves an ultra-wide I/Q phase tuning range without affecting the oscillator other performance metrics. The proposed topology was successfully verified in silicon using a 5GHz prototype. The third part of this work introduces a new low-power, low-phase-noise injection coupled QVCO (IC-QVCO) topology. An X-band IC-QVCO prototype was successfully verified in a 0.18m RF CMOS process. In the fourth part of this work, we explore the implementation of QVCOs as potential I/Q sources at millimeter-wave (MMW) frequencies. Among the several design challenges that emerge as the oscillator frequency is scaled into the MMW band, precise quadrature synthesis and adequate frequency tuning range are among the hardest to achieve. After describing the limitation of using an conventional frequency tuning techniques, we propose an alternative approach based on the fundamental operation of QVCOs that outperforms existing solutions.

The increasing number of mobile devices challenges the current radio frequency (RF) networks. The conventional RF spectrum for wireless communications is saturating, motivating to develop other unexplored frequency bands. Light Fidelity (LiFi) which uses more than 300 THz of the visible light spectrum for high-speed wireless communications, is considered a promising complementary technology to its RF counterpart. LiFi enables daily lighting infrastructures, i.e. light emitting diode (LED) lamps to realise data transmission, and maintains the lighting functionality at the same time. Since LiFi mainly relies on line-of-sight (LoS) transmission, users in indoor environments may experience blockages which significantly affects users' quality of service (QoS). Therefore, hybrid LiFi and RF networks (HLRNs) where LiFi supports high data rate transmission and RF offers reliable connectivity, can provide a potential solution to future indoor wireless communications. In HLRNs, efficient load balancing (LB) schemes are critical in improving the traffic performance and network utilisation. In this thesis, the optimisation-based scheme (OBS) and the evolutionary game theory (EGT) based scheme (EGTBS) are proposed for load balancing in HLRNs. Specifically, in OBS, two algorithms, the joint optimisation algorithm (JOA) and the separate optimisation algorithm (SOA) are proposed. Analysis and simulation results show that JOA can achieve the optimal performance in terms of user data rate while requiring high computational complexity. SOA reduces the computational complexity but achieves low user data rates. EGTBS is able to achieve a better performance/complexity trade-off than OBS and other conventional load balancing schemes. In addition, the effects of handover, blockages, orientation of LiFi receivers, and user data rate requirement on the throughput of HLRNs are investigated. Moreover, the packet latency in HLRNs is also studied in this thesis. The notion of LiFi service ratio is introduced, defined as the proportion of users served by LiFi in HLRNs. The optimal LiFi service ratio to minimise system delay is mathematically derived and a low-complexity packet flow assignment scheme based on this optimum ratio is proposed. Simulation results show that the theoretical optimum of the LiFi service ratio is very close to the practical solution. Also, the proposed packet flow assignment scheme can reduce at most 90% of packet delay compared to the conventional load balancing schemes at reduced computational complexity.

The investigation of liquid crystal polymer (LCP) technology to function as a low-cost next-generation organic platform for designs up to millimeter-wave frequencies has been performed. Prior to this research, the electrical performance of LCP had been characterized only with the implementation of standard transmission lines and resonators. In this research, a wide variety of passive functions have been developed on LCP technology and characterized for the first time. Specifically, we present the development of patch antenna arrays for remote sensing applications, the performance of compact low-pass and band-pass filters up to millimeter-wave frequencies, and the integration of passive elements for X-band and V-band transceiver systems. First, dual-frequency/dual-polarization antenna arrays have been developed on multilayer LCP technology and have been integrated with micro-electro-mechanical-system (MEMS) switches to achieve real-time polarization reconfigurability. These arrays are conformal, efficient and have all the features desirable for applications that require space deployment. Second, a wide variety of filters with different physical and functional characteristics have been implemented on both single and multilayer LCP technology. These filters can be classified based on the filter type (low-pass/band-pass), the resonators used (single-mode/dual-mode), the response characteristics (symmetric/asymmetric), and the structure of the filter (modular/non-modular). Last, examples of integrated modules for use in transceiver systems are presented. This part of the research involves the development of duplexers, radiating elements, as well as their integration. The duplexers themselves are realized by integrating a set of band-pass filters and matching networks. The characterization of the individual components, and of the integrated system are included. This research has resulted in a thorough understanding of LCP's electrical performance and its multilayer lamination capabilities pertaining to its functioning as a material platform for integrated microwave systems. Novel passive prototypes that can take advantage of such multilayer capabilities have been developed.

The growing demand for wireless communication systems is driving the integration of radio frequency (RF) front-ends on the same chip with multi-band functionality and higher spectral efficiency. Microelectromechanical systems (MEMS) have an overarching applicability to RF communications and are critical components in facilitating this integration process. Among a variety of RF MEMS devices, piezoelectric MEMS resonators have sparked significant research and commercial interest for use in oscillators, filters, and duplexers. Compared to their bulky quartz crystal and surface acoustic wave (SAW) counterparts, MEMS resonators exhibit impressive advantages of compact size, lower production cost, lower power consumption, and higher level of integration with CMOS fabrication processes. One of the promising piezoelectric MEMS resonator technologies is the aluminum nitride (AlN) contour mode resonator (CMR). On one hand, AlN is chemically stable and offers superior acoustic properties such as large stiffness and low loss. Furthermore, CMRs offer low motional resistance over a broad range of frequencies (few MHZ to GHz), which are lithographically-definable on the same silicon substrates. To date, RF MEMS resonators (include CMRs) have been extensively studied; however, one aspect that was not thoroughly investigated is how to modulate/tune their equivalent parameters to enhance their performance in oscillators and duplexers. The goal of this thesis is to investigate various modulation methods to improve the thermal stability of the resonator, its “effective” quality factor when used in an oscillator, and build completely novel non-reciprocal components. Broadly defined, modulation refers to the exertion of a modifying or controlling influence on something, herein specifically, the resonator admittance. In this thesis, three categories of modulation methods are investigated: thermal modulation, force modulation, and external electronic modulation. Firstly, the AlN CMR’s center frequency can be tunned by the applied thermal power to the resonator body. The resonator temperature is kept constant (for example, 90 °C) via a temperature sensor and feedback control such that the center frequency is stable over the whole operation temperature range of interest (e.g. –35 to 85 °C). The maximum power consumption to sustain the maximum temperature difference (120 ºC in this thesis) between resonator and ambient is reduced to a value as low as 353 μW – the lowest ever reported for any MEMS device. These results were attained while simultaneously maintaining a high quality factor (up to 4450 at 220 MHz device). The feedback control was implemented by either analog circuits or via a microprocessor. The analog feedback control, which innovatively utilized a dummy resistor to compensate for temperature gradients, resulted in a total power consumption of 3.8 mW and a frequency stability of 100 ppm over 120 ºC. As for the digital compensation, artificial neural network algorithm was employed to facilitate faster calibration of look-up tables for multiple frequencies. This method attained a frequency stability of 14 ppm over 120 ºC. The second modulation method explored in this thesis is based on the use of an effective external force to enhance the 3-dB quality factor of AlN CMRs and improve the phase noise performance of resonator-based oscillators. The force modulation method was embodied in a two-port device, where one of the two ports is used as a one-port resonator and the other is driven by an external signal to effectively apply an external force to the first port. Through this technique, the quality factor of the resonator was boosted by 140 times (up to 150,000) and the phase noise of the corresponding oscillator realized using the resonator was reduced by 10 dBc/Hz. Lastly, a novel magnetic-free electrical circulator topology that facilitates the development of in-band full duplexers (IBFD) for simultaneous transmit and receive (STAR) is proposed and modeled. Fundamentally, a linear time-invariant (LTI) filter network parametrically modulated via a switching matrix is used to break the reciprocity of the filter. The developed model accurately predicts the circulator behavior and shows very good agreement with the experimental results for a 21.4 MHz circulators built with MiniCircuit filter and switch components. Furthermore, a high frequency (1.1 GHz) circulator was synthesized based on AlN MEMS bandpass filters and CMOS RF switches, hence showing a compact approach that can be used in handheld devices. The modulation frequency and duty cycle are optimized so that the circulator can provide up to 15 dB of isolation over the filter bandwidth while good power transfer between the other two ports is maintained. The demonstrated device is expected to intrinsically offer low noise and high linearity. The combination of the first two modulation methods facilitates the implementation of monolithic, temperature-stable, ultra-low noise, multi-frequency oscillator banks. The third modulation technique that was investigated sets the path for the development of CMOS-compatible in-band full duplexers for simultaneous transmit and receive and thus facilitates the efficient utilization of the electromagnetic spectrum. With the aid of all these three modulation approaches, the author believes that a fully integrated, multi-frequency, spectrum-efficient transceiver is enabled for next-generation wireless communications.

Microelectromechanical systems (MEMS) devices have been increasing in popularity for radio frequency (RF) and microwave communication systems due to the ability of MEMS devices to improve the performance of these circuits and systems. This interdisciplinary field combines the aspects of lithographic fabrication, mechanics, materials science, and RF/microwave circuit technology to produce moving structures with feature dimensions on the micron scale (micro-structures). MEMS technology has been used to improve switches, varactors, and inductors to name a few specific examples. Most MEMS devices have been fabricated using planar micro fabrication techniques that are similar to current integrated circuit (IC) fabrication techniques. These techniques limit the thickness of individual layers to a few microns, and restrict the structures to have planar and not vertical features. One micro fabrication technology that has not seen much application to microwave MEMS devices is LIGA, a German acronym for X-ray lithography, electroforming, and moulding. LIGA uses X-ray lithography to produce very tall structures (hundreds of microns) with excellent structural quality, and with lateral feature sizes smaller than a micron. These unique properties have led to an increased interest in LIGA for the development of high performance microwave devices, particularly as operating frequencies increase and physical device size decreases. Existing work using LIGA for microwave devices has concentrated on statically operating structures such as transmission lines, filters, couplers, and antennas. This research uses these unique fabrication capabilities to develop dynamically operating microwave devices with high frequency performance. This thesis documents the design, fabrication and testing of LIGA-MEMS variable capacitors that exploit the vertical dimension. Also included are methods to improve both the reliable fabrication and operation of these devices as well as material property characterization. Variable capacitors can be found in systems such as voltage-controlled oscillators, filters, impedance matching networks and phase shifters. Important figures-of-merit for these devices include the quality factor (Q), tuning range and tuning voltage. Two different types of variable capacitors are presented, a pull-away design and a design based on the principle of leveraged bending. The pull-away style variable capacitors were found to have high Q-factors, especially the devices fabricated using a thick gold device layer. As an example, the small gold half capacitance electrode design features a Q-factor of 95 at an operating frequency of 5.6 GHz and a tuning ratio of 1.36:1 with a tuning voltage range of 0 to 7.8 V. The design based on leveraged bending significantly improves the tuning ratio to a value of 1.9:1 while still maintaining a high Q-factor similar to those found in the pull-away style designs. A further increase in tuning ratio to a value of approximately 2.7:1 would be possible, based on simulated results, by simply changing the angle of the capacitance electrode in the layout. To improve device performance and fabrication reliability, modifications were made to both the fabrication process and the device layout. In the fabrication process the exposure step, electroplating step, and the etching process were modified to improve the quality of the resulting devices. In the layout, anti-stiction measures were introduced that reduce the contact area during collapse. To improve device characterization as well as the feedback link between simulation and fabrication, a set of test structures called VM-TEST was developed to accurately determine the important mechanical material properties of thick electroplated layers. These structures utilize the measurement of the pull-in voltage in cantilever and fixed-fixed beams, along with measured structure dimensions, to accurately extract the mechanical properties. Both nickel and gold test structures were analyzed with extracted Young’s modulus values of 186.2 and 60.8 GPa respectively. Also presented is a study of the gap shape in cantilever and fixed-fixed beams that significantly reduces the pull-in voltage while still maintaining a required maximum actuator displacement. It was shown that in the case of cantilever beam actuators, an approximately 40% reduction in pull-in voltage is possible, and in the case of fixed-fixed beam actuators, an approximately 30% reduction is possible by simply varying the shape of the gap between the beam and actuator electrode. These results can be used to significantly reduce the pull-in voltage of future designs. These promising results show that the LIGA fabrication process is capable of producing high performance dynamically operating RF MEMS devices, by exploiting the vertical dimension, not typically performed in most existing RF MEMS designs.