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The fifth generation (5G) has developed a lot of interest, and there have been many reported initiatives in both industry and academics. Multiple-input-multiple-output (MIMO) is the most promising wireless access technique for next-generation networks in terms of spectral and energy efficiency (MIMO). In 4G systems, 2-Element MIMO antennas are already used, while 5G mobile terminals for smartphone hand-held devices are projected to use a bigger number of elements. The placement of many antennas in the restricted space of a smartphone PCB is one of the most critical challenges. As a result, for sub-6 GHz 5G applications, a new design technique based on dual-polarised antenna resonators for 6-Element, 8-Element MIMO configuration is proposed. The proposed MIMO design could improve the smartphone antenna system's chan-nel capacity, diversity function, and multiplexing gain, making it appropriate for 5G applica-tions. For distinct prospective bands of the sub-6 GHz spectrum, such as 2.6, 3.6, and 5.8 GHz, different types of novel and compact diversity MIMO antennas using Patch, Slot, and Planar inverted F antenna (PIFA) resonators are examined. Unlike previously reported MIMO antennas, the proposed designs provide full radiation coverage and polarisation diversity, as well as adequate gain and efficiency values to support several mainboard sides. Apart from sub-6 GHz frequencies, 5G devices are projected to support the centimetre/milli-metre wave spectrum's higher bands. To create linear phased arrays, small antennas can be placed at various locations on a smartphone board. For 5G smartphones, we propose novel linear phased arrays with tiny parts like Dipole and Quasi-Yagi resonators. In comparison to previously published designs, the suggested phased arrays have desirable qualities such as compact size, wide beam-steering, broad bandwidth, end-fire radiation, high gain, and efficiency. With a reduced mutual coupling function, the suggested 5G antennas can provide single-band, multi-band, and broad-band characteristics. Both models and measurements are used to an-alyse the fundamental features of 5G antennas, and good agreement is found. Furthermore, in the presence of the user and the smartphone components, good features are seen due to the small size and superior arrangement of elements. Because of these benefits, the sug-gested antennas are well-suited for usage in 5G smartphone applications.

Phased array element RF front ends typically use single pole double throw (SPDT) switches or circulators with high isolation to prevent leakage of transmit energy into the receiver circuits. However, as phased-array designs scale to the millimeter-wave range, with high degrees of integration, the physical size and performance degradations associated with switches and circulators can present challenges in meeting system performance and size/weight/power (SWAP) requirements. This work demonstrates a loss-aware methodology for analysis and design of switchless transmit/receive (T/R) circuits. The methodology provides design insights and a practical, generally applicable approach for solving the multi-variable optimization problem of switchless power amplifier/low-noise amplifier (PALNA) matching networks, which present optimal matching impedances to both the power amplifier (PA) and the low noise amplifier (LNA) while maximizing power transfer efficiency and minimizing dissipative losses in each (transmit or receive) mode of operation. Three PALNA example designs at W-band are presented in this dissertation, each following a distinct design methodology. The first example design in 32SOI CMOS leverages PA and LNA circuits that already include 50 Ω matching networks at both input and output. The second example design in 8XP SiGe develops the PA and LNA circuits and integrates the PA output and LNA input matching networks into the PALNA matching network that connects the PA and the LNA. The third design in 32SOI CMOS leverages the loss-aware PALNA design methodology to develop a PALNA that achieves simulated maximum power added efficiency of 18 % in transmit and noise figure of 7.5 dB in receive at 94 GHz, which is beyond the published state-of-art for T/R circuits. In addition, for comparison purposes, this dissertation also presents an efficient, switch-based T/R circuit design in 32SOI CMOS technology, which achieves a simulated maximum power added efficiency of 15 % in transmit and noise figure of 6.5 dB in receive at 94 GHz, which is also beyond the published state-of-art for T/R circuits. / Doctor of Philosophy / In military and commercial applications, phased arrays are devices primarily used to achieve focusing and steering of transmitted or received electromagnetic energy. Phased arrays consist of many elements, each with an ability to both transmit and receive radio frequency (RF) signals. Each element incorporates a power amplifier (PA) for transmit and a low noise amplifier (LNA) for receive, which are typically connected using a single pole double throw (SPDT) switch or a circulator with high isolation to prevent leakage of transmit energy into the receiver circuits. However, as phased arrays exploit the latest technological advances in circuit integration and their frequencies of operation increase, physical size and performance degradations associated with switches and circulators can present challenges in meeting system performance and size/weight/power (SWAP) requirements. This dissertation provides a loss-aware methodology for analysis and design of switchless transmit/receive (T/R) circuits where the switches and circulators are replaced by carefully designed power amplifier/low-noise amplifier (PALNA) impedance matching networks. In the switchless T/R circuits, the design goals of maximum power efficiency and minimum noise in transmit and receive, respectively, are achieved through impedance matching that is optimal and low-loss in both modes of operation simultaneously. Three distinct PALNA example designs at W-band are presented in this dissertation, each following a distinct design methodology. With each new design, lessons learned are leveraged and design methodologies are enhanced. The first example design leverages already available PA and LNA circuits and connects them using 50 Ω transmission lines whose lengths are designed to guarantee optimum impedance match in receive and transmit mode of operation. The second example design develops new PA and LNA circuits and connects them using 50 Ω transmission lines whose lengths are designed to simultaneously achieve optimum impedance matching for maximum power efficiency in transmit mode of operation and lowest noise in receive mode of operation. The third design leverages a loss-aware PALNA design methodology, a multi-variable optimization procedure, to develop a PALNA that achieves simulated maximum power added efficiency of 18 % in transmit and noise figure of 7.5 dB in receive at 94 GHz, which is beyond the published state-of-art for T/R circuits. In addition, for comparison purposes with the third PALNA design, this dissertation also presents an efficient, switch-based T/R circuit design, which achieves a simulated maximum power added efficiency of 15 % in transmit and noise figure of 6.5 dB in receive at 94 GHz, which is also beyond the published state-of-art for T/R circuits.

<p><br></p><p dir="ltr">Over the past decade, optical frequency combs have spurred significant advancements in both classical ultrafast optics and quantum optics. My research contributes to these two fields, catering to applications in precision metrology and optical networking. In the domain of quantum optics, the study delves into biphoton frequency combs with time-energy entanglement, employing novel electro-optic modulation schemes to enhance sensitivity and enable precise measurements of temporal correlations. Additionally, Bell states, a crucial class of entangled quantum bases, are generated in the frequency domain, showcasing their utility in delay metrology and quantum cryptographic protocols. </p><p dir="ltr">In the realm of classical optical frequency combs, this work explores dynamic steering of pulsed optical beams, holding promise for applications in imaging and remote sensing. The concept of time-efficient dynamic beam steering using a spatial array of optical frequency combs is elucidated and experimentally demonstrated through the utilization of a high-resolution spectral disperser, specifically a virtually imaged phased array (VIPA). Furthermore, integrated photonic designs featuring wavelength-selective switches and spectral dispersers are proposed to enable a versatile on-chip implementation of the beam steering approach. In sum, this research leverages the capabilities of classical and quantum optical frequency combs, with implications for emerging applications such as distributed sensing, quantum networking, and light detection and ranging (LIDAR).</p>

Phased array weather radar antennas with beam steering capabilities are suitable alternatives to weather radars with mechanically scanning reflector antennas. Dual-polarized phased-array weather radar antennas, however, demand careful assessment of the x-polar characteristics. The low x-pol radiation of polarimetric weather radar antennas is of significant importance for the proper classification and qualitative estimation of hydrometeors in illuminate volumes. Unfortunately, array antennas display changing x-pol contributions during the electronical beam steering process. Typically, the x-pol radiation will be substantially increased in the co-polar main beam direction but also in other angular directions. Consequently, it is a vital challenge to design arrays with low x-pol contribution during beam steering. In this dissertation a new phased-array weather radar concept is developed. The phased array system configuration can be used to substitute state-of-the-art weather radars with reflector antennas. Furthermore, a dense network of these phased-array radars can be used to substitute a network of high power weather radars, which are used nowadays. The research focus of this work is the development of a dual-polarized microstrip patch antenna with phased-array capability and very high polarization purity. In this regard, new graphical techniques are developed to investigate the causes and the reduction of the x-pol radiation of isolated (stand-alone) microstrip patch antennas. To further reduce the x-pol contribution of antennas, optimization methods have been investigated, evaluated and developed. For the first time in literature, differential-feed antenna arrays are compared to excitation optimized single-feed antenna arrays in their x-pol contribution in the boresight direction and during beam steering. In particular, two dual-polarized 4x8 antenna arrays have been developed and simulated by CST MWS, produced as multilayer PCB and verified at the compact antenna test range at RWTH Aachen. The results show that the x-pol contributions of arrays are significantly reduced for differentially-feed antenna arrays, even when beam steering is performed. During the azimuth scan of 120_ a record setting x-pol suppression of -45 dB and -36 dB could be measured for the horizontal and vertical polarization channels, respectively. / Wetterradarsysteme mit phasengesteuerten Antennen stellen eine echte Alternative zu Wetterradarsystemen mit mechanisch drehenden Reflektorantennen dar. Dual-polarisierte phasengesteuerte Antennen müssen jedoch sehr genau in ihrem Kreuzpolarisationsverhalten verifiziert werden, um für den Wetterradarbereich von Nutzen zu sein. Die Unterdrückung der kreuzpolaren Anteile von Radarantennen ist von fundamentaler Bedeutung, um Hydrometeore mit Hilfe von polarimetrischen Wetterradarsystemen klassifizieren und qualitativ bestimmen zu können. Die hohe Anforderung an Polarisationsreinheit ist mit aktuell erhältlichen Arraydesigns nur schwierig zu realisieren, da sich die Kreuzpolarisationsunterdrückung während des elektronischen Schwenks der Hauptkeule signifikant verschlechtert. Diese Dissertation stellt ein Wetterradar Systemkonzept mit phasengesteuerter Gruppenantenne vor, welches die aktuell genutzten Wetterradare mit Reflektorantennen ablösen könnte. Der Fokus der Arbeit wurde auf die Entwicklung einer Dual-polarimetrischen, polarisationsreinen und phasengesteuerten Mikrostreifenleiterantennen gelegt. Hierbei wurden neue grafische Verfahren entwickelt, die es ermöglichen, die Generierung der kreuzpolaren Anteile von isolierten Patchantennen (Einzelpatche) zu erklären und zu minimieren. Um die kreuzpolaren Anteile weiter herabzusetzen wurden Optimierungsverfahren für Arrayantennen erforscht, bewertet und neu entwickelt. Zum ersten Mal wurden differentiell gespeiste mit einzeln gespeisten Antennenarrays in ihrem Kreuzpolarisationsverhalten während des elektronischen Schwenks der Hauptkeule verglichen. Zwei Dual- polarimetrische 4x8 Antennenarrays (differentiell gespeist und mit optimierter Phasenansteuerung) wurden zu diesem Zweck mittels CST MWS entworfen, simuliert, als Multilagenplatine gefertigt und an der Antennentestanlage der RWTH Aachen vermessen. Die Resultate zeigen, dass die Kreuzpolarisationsanteile bei differentiell gespeisten Mikrostreifenleiterantennen in Gruppenkonfiguration, selbst beim elektronischen Schwenk der Hauptkeule, signifikant minimiert werden konnten. Für einen azimutalen Scanbereich von 120_ konnte eine exzellente Kreuzpolarisationsunterdrückung zwischen -45 dB und -36 dB messtechnisch für den horizontalen und vertikalen Polarisationskanal nachgewiesen werden.

Monitoring the mechanical integrity of critical structures is extremely important, as mechanical defects can potentially have adverse impacts on their safe operability throughout their service life. Structural defects can be detected by using active structural health monitoring (SHM) approaches, in which a given structure is excited with harmonic mechanical waves generated by actuators. The response of the structure is then collected using sensor(s) and is analyzed for possible defects, with various active SHM approaches available for analyzing the response of a structure to single- or multi-frequency harmonic excitations. In order to identify the appropriate excitation frequency, however, the majority of such methods require a priori knowledge of the characteristics of the defects under consideration. This makes the whole enterprise of detecting structural defects logically circular, as there is usually limited a priori information about the characteristics and the locations of defects that are yet to be detected. Furthermore, the majority of SHM techniques rely on sensors for response collection, with the very same sensors also prone to structural damage. The Surface Response to Excitation (SuRE) method is a broadband frequency method that has high sensitivity to different types of defects, but it requires a baseline. In this study, initially, theoretical justification was provided for the validity of the SuRE method and it was implemented for detection of internal and external defects in pipes. Then, the Comprehensive Heterodyne Effect Based Inspection (CHEBI) method was developed based on the SuRE method to eliminate the need for any baseline. Unlike traditional approaches, the CHEBI method requires no a priori knowledge of defect characteristics for the selection of the excitation frequency. In addition, the proposed heterodyne effect-based approach constitutes the very first sensor-less smart monitoring technique, in which the emergence of mechanical defect(s) triggers an audible alarm in the structure with the defect. Finally, a novel compact phased array (CPA) method was developed for locating defects using only three transducers. The CPA approach provides an image of most probable defected areas in the structure in three steps. The techniques developed in this study were used to detect and/or locate different types of mechanical damages in structures with various geometries.

Abnormal electromagnetic wave propagation characterized by negative group velocity and consequently negative group delay (NGD) has been observed in certain materials as well as in artificially built structures. Within finite frequency intervals where an NGD phenomenon is observed, higher frequency components of the applied waveform are propagated with phase advancement, not delay, relative to the lower frequency components. These media have found use in many applications that require positive delay compensation and an engineered phase characteristic, such as eliminating phase variation with frequency in phase shifters, beam-squint minimization in phased array antenna systems, size reduction of feed-forward amplifiers and others. The three principal questions this thesis addresses are: can a generic formulation for artificial NGD structures based on electric circuit resonators be developed; is it possible to derive a quantitative functional relationship (asymptotic limit) between the maximum achievable NGD and the identified trade-off quantity (out-of-band gain); and, can a microwave circuit exhibiting a fully loss-compensated NGD propagation in both directions be designed and implemented? A generic frequency-domain formulation of artificial NGD structures based on electric circuit resonators is developed and characterized by three parameters, namely center frequency, bandwidth and the out-of-band gain. The developed formulation is validated through several topologies reported in the literature. The trade-off relationship between the achievable NGD on one hand, and the out-of-band gain on the other, is identified. The out-of-band gain is shown to be proportional to transient amplitudes when waveforms with defined “turn on/off” times are propagated through an NGD medium. An asymptotic limit for achievable NGD as a function of the out-of-band gain is derived for multi-stage resonator-based NGD circuits as well as for an optimally engineered linear causal NGD medium. Passive NGD media exhibit loss which can be compensated for via active elements. However, active elements are unilateral in nature and therefore do not allow propagation in both directions. A bilateral gain-compensated circuit is designed and implemented, which overcomes this problem by employing a dual-amplifier configuration while preserving the overall circuit stability.

Wireless operation, near-field or far-field, is a core functionality of any mobile or autonomous system. These systems are battery operated or most often utilize energy scavenging as a means of power generation. Limited access to power, expected long and uninterrupted operation, and constrained physical parameters (e.g. weight and size), which limit overall power harvesting capabilities, are factors that outline the importance for innovative low-power approaches and designs in advanced low-power wireless applications. Low-power approaches become especially important for the wireless transceiver, the block in charge of wireless/remote functionality of the system, as this block is usually the most power hungry component in an integrated system-on-chip (SoC). Three such advanced applications with stringent power requirements are examined including space-based exploratory remote sensing probes and their associated radiation effects, millimeter-wave phased-array radar for high-altitude tactical and geological imaging, and implantable biomedical devices (IMDs), leading to the proposal and implementation of low-power wireless solutions for these applications in SiGe BiCMOS and CMOS and platforms.

Abnormal electromagnetic wave propagation characterized by negative group velocity and consequently negative group delay (NGD) has been observed in certain materials as well as in artificially built structures. Within finite frequency intervals where an NGD phenomenon is observed, higher frequency components of the applied waveform are propagated with phase advancement, not delay, relative to the lower frequency components. These media have found use in many applications that require positive delay compensation and an engineered phase characteristic, such as eliminating phase variation with frequency in phase shifters, beam-squint minimization in phased array antenna systems, size reduction of feed-forward amplifiers and others. The three principal questions this thesis addresses are: can a generic formulation for artificial NGD structures based on electric circuit resonators be developed; is it possible to derive a quantitative functional relationship (asymptotic limit) between the maximum achievable NGD and the identified trade-off quantity (out-of-band gain); and, can a microwave circuit exhibiting a fully loss-compensated NGD propagation in both directions be designed and implemented? A generic frequency-domain formulation of artificial NGD structures based on electric circuit resonators is developed and characterized by three parameters, namely center frequency, bandwidth and the out-of-band gain. The developed formulation is validated through several topologies reported in the literature. The trade-off relationship between the achievable NGD on one hand, and the out-of-band gain on the other, is identified. The out-of-band gain is shown to be proportional to transient amplitudes when waveforms with defined “turn on/off” times are propagated through an NGD medium. An asymptotic limit for achievable NGD as a function of the out-of-band gain is derived for multi-stage resonator-based NGD circuits as well as for an optimally engineered linear causal NGD medium. Passive NGD media exhibit loss which can be compensated for via active elements. However, active elements are unilateral in nature and therefore do not allow propagation in both directions. A bilateral gain-compensated circuit is designed and implemented, which overcomes this problem by employing a dual-amplifier configuration while preserving the overall circuit stability.

Photonics and Optical techniques have advanced recently by a great extend to play an important role in Microwave and Radar applications. Antenna array of modern active phased array radars consist of multiple low power transmit and receive mod- ules. This demands distribution of the various Local Oscillator(LO) signals for up conversion of transmit signals and down conversion of receive signals during various modes of operation of a radar system. Additionally, these receivers require control and clock signals which are digital and low frequency analog, for the synchronization between receive modules. This is normally achieved through RF cables with complex distribution networks which add significantly higher additional weight to the arrays. During radar operations, radio frequency (RF) transmit signal needs to be distributed through the same modules which will in turn get distributed to all antenna elements of the array using RF cables. This makes the system bulky and these large number of cables are prone to Electromagnetic Interference (EMI) and need additional shielding. Therefore it is very desirable to distribute a combination of these RF, analog and digital signals using a distribution network that is less complex, light in weight and immune to EMI. Advancements in Optical and Microwave photonics area have enabled carrying of higher datarate signals on a single fiber due to its higher bandwidth capability including RF signals. This is achieved by employing Wavelength Division Multi- plexing (WDM) that combine high speed channels at different wavelengths. This work proposes, characterizes and evaluates an optical Wavelength Division Multiplexed(WDM) distribution network that will overcome the above mentioned problems in a phased array radar application. The work carries out a feasibility analysis supported with experimental measurements of various physical parameters like am- plitude, delay, frequency and phase variation for various radar waveforms over WDM links. Different configurations of optical distribution network are analyzed for multipoint distribution of both digital and RF signals. These network configurations are modeled and evaluated against various parameters that include power level, loss, cost and component count. A configuration which optimizes these parameters based on the application requirements is investigated. Considerable attention is paid to choose a configuration which does not provide excess loss, which is economically viable, compact and can be realized with minimum component count. After analysing the link configuration, multiplexing density of the WDM link is considered. In this work, since the number of signals to be distributed in radar systems are small, a coarse WDM(CWDM) scheme is considered for evaluation. A comparative study is also performed between coarse and dense WDM (DWDM) links for selection of a suitable multiplexing scheme. These configurations are modeled and evaluated with power budgeting. Even though CWDM scheme does not permit the utilisation of the available bandwidth to the fullest extent, these links have the advantage of having less hardware complexity and easiness of implementation. As the application requires signal distribution to thousands of transmit-receive modules, amplifiers are necessary to compensate for the reduction of signal level due to the high splitting ratio. Introduction of commonly available optical amplifiers like Erbium Doped Fiber Amplifier (EDFA), affect the CWDM channel output powers adversely due to their non-flat gain spectrum. Unlike DWDM systems, the channel separation of CWDM systems are much larger causing significantly high channel gain differences at the EDFA output. So an analysis is carried out for the selection of a suitable wavelength for CWDM channels to minimize the EDFA output power variation. If the gain difference is still significant, separate techniques needs to be implemented to flatten the output power at the antenna end. A CWDM configuration using C-band and L-band EDFAs is proposed and is supported with a feasibility analysis. As a part of evaluation of these links for radar applications, a mathematical model of the WDM link is developed by considering both the RF and digital sig- nals. A generic CWDM system consisting of transmitters, receivers, amplifiers, multiplexers/ demultiplexers and detectors are considered for the modeling. For RF signal transmission, the transmitters with external modulators are considered. Mod- eling is done based on a bottom-top approach where individual component models are initially modeled as a function of input current/power and later cascaded to obtain the link model. These models are then extended to obtain the wavelength dependent model ( spectral response) of the hybrid signal distribution link Further mathematical analysis of the developed link model revealed its variable separable nature in terms of the input power and wavelength. This led to significant reduction in the link equation complexity and development of some approximation techniques to easily represent the link behavior. The reduced form of the link spectral model was very essential as the initially developed wavelength model had a lot of parametric dependency on the component models. This mathematical reduction process led to simplification of the spectral model into a product of two independent functions, the input current and wavelength. It is also noticed that the total link power within specific wavelength range can be obtained by the integrating these functions over a specific link input power. After the mathematical modelling, an experimental prototype physical link is set up and characterized using various radar signals like continuous wave (CW) RF, pulsed RF, non linear frequency modulated signal (NLFM) etc. Additionally a proof of concept Radio-Over-Fiber (RoF) link is established to prove the superior transmission of microwave signal through an optical link. The analysis is supported with measurements on amplitude, delay, frequency and phase variations. The NLFM waveforms transmissions are further analysed using a matched _ltering process to confirm the side lobe requirement. Further a prototype WDM link is built to study the performance when digitally modulated channels are also multiplexed into the link. The link is again validated for signal levels, delay, frequency and phase parameters. Since amplitude and delay are deterministic, it is proposed that these parameter variations can be compensated by using suitable components either in the electrical or the optical domain. Radar systems use low frequency digital signals of different duty-cycles for synchronization and control across various transmit-receive modules. In the proposed link, these digital signals also modulate a WDM channel and hence the link is called a hybrid system. As the proposed link has EDFA to compensate for the splitting losses, there are chances of transient effects at the EDFA output for these low bitrate channels. Owing to the long carrier lifetime, low bitrate digital channels are prone to EDFA transient effects under specific signal and pump power conditions. Additionally, the synchronization signals used in radar application vary the duty-cycle over time, which is found to introduce variations in transient output. This practical challenge is further studied and the thesis for the first time, includes an analysis of EDFA transient e_ects for variable duty-cycle pulsed signals. The analysis is carried out for various parameters like bitrate, input power, pump power and duty-cycle. Investigations on EDFA transients on variable duty-cycle signals help in proposing a viable method to predict the lower duty-cycle transients from higher duty-cycle transients. The predicted transients were again validated against simulated transients and experimental results. As these transient effects are not desirable for radar signals, we propose a novel transient suppression techniques in optical and electrical domain which are validated with simulation and experimental measures. One suppression technique tries to avoid transient effect by keeping the optical input to EDFA always constant by feeding an inverted version of the original pulse into the EDFA along with the actual pulse. It is observed that as the wavelength of the inverted pulse is closer to the original input pulse, the transient effect settles faster. These EDFA transients are evaluated with WDM link configurations, where both high and low bitrate signals are co-propagated. Another challenging aspect of the link operation is the non-at gain spectrum of EDFA. i.e., EDFA provides unequal power level for various signals at WDM link output. This is especially true in the case of local oscillator signals, where it is preferable to have the same amplitude signals before feeding it to the mixer stages. But in the radar applications, this will require additional hardware circuits to equalize the signal level within a phased array antenna. This work also proposes some of the power equalization methods that can be used along with the WDM links. This part of the work is also supported with simulation model and experimental results. The analytical and experimental study of this thesis aids the evaluation process of a suitable optical Wavelength Division Multiplexed(WDM) distribution network that can be used for the distribution of both RF and digital signals. The optical WDM links being superior with its light weight, less loss and EMI/ EMC immunity provides a better solution to future class of radars.