Terahertz (THz) waves (300 GHz to 10 THz) constitute the least studied part of the electromagnetic (EM) spectrum with unique propagation properties that make them attractive to emerging sensing and imaging application. As opposed to optical signals, THz waves can penetrate several non-metallic materials (e.g., plastic, wood, and thin tissues), thus enabling several applications in security monitoring, non-destructive evaluation, and biometrics. Additionally, THz waves scatter on most surfaces distinctively compared with lower/higher frequencies (e.g., microwave/optical bands). Therefore, based on these two interesting THz wave propagation properties, namely penetration and scattering, I worked on THz imaging methods that explore non-line-of-sight (NLoS) information. First, I use a THz microscopy method to probe the fingertips as a new technique for fingerprint scanning. Due to the wave penetration in the THz range, I can exploit sub-skin traits not visible with current approaches to obtain a more robust and secure fingerprint scanning method. I also fabricated fingerprint spoofs using latex to compare the imaging results between real and fake fingers. Next, I focus on THz imaging hardware topologies and algorithms for longer-distance imaging applications. As such, I compare the imaging performance of dense and sparse antenna arrays through simulations and measurements. I show that sparse arrays with nonuniform amplitudes can provide lower side lobes in the images. Besides, although sparse arrays feature a much smaller total number of elements, dense arrays have advantages when imaging scenarios with multiple objects. Afterward, I propose a THz imaging method to see around obstacles/corners. THz waves’ unique scattering properties are helpful to implement around-the-corner imaging. I carried out both simulations and measurements in various scenarios to validate the proposed method. The results indicate that THz waves can reveal the hidden scene with centimeter-scale resolution using proper rough surfaces and moderately sized apertures. Moreover, I demonstrate that this imaging technique can benefit simultaneous localization and mapping (SLAM) in future communication systems. NLoS images enable accurate localization of blocked users, hence increasing the link robustness. I present both simulation and measurement results to validate this SLAM method. I also show that better localization accuracy is achieved when the user's antenna is omnidirectional rather than directional.

Data transmission and reception has become an important aspect in day-to-day communication. With advancement in technology, it dictates the need for accurate data transmission and reception. For this very reason, wireless transceivers are employed in almost every industrial domain for numerous applications. A special concept of distributed transceivers is proven to be extremely useful in the latest technologies like Internet of Things. As the name suggests, this is a collaborative communication technique where multiple transceivers are synchronized for faster and much more reliable communication. This imposes a major challenge while designing this kind of a transceiver, as all the transceivers should be operating with carrier synchronization to maintain the proper collaboration. While there are several ways to establish this sync, this thesis emphasizes one of those techniques and tries to resolve the issue in design. The carrier synchronization is achieved using time division synchronization technique. Several challenges in implementing this technique were addressed using various models simulated in MATLAB Simulink and Keysight ADS. An in detail analysis has been performed for all the techniques used for this implementation to provide a diverse perspective.

Satellite communications employs circular polarization (CP) to circumvent thewell-known phenomenon known as Faraday Rotation, where the ionosphere rotates the horizontal and vertical polarization components resulting in signal degradation especially at lower frequencies, i.e., VHF and L-band, and in tropical regions of the earth. Satellite circularly polarized antenna feed technology commonly employs bulkyand lossy 90-degree hybrid combiners to convert linear polarization to circular polarization, which results in a higher noise figure for receive applications and a less repeatable and more difficult design to tune and manufacture. This thesis aims at designing, modeling and simulating a prototype S/X dual bandCP feed/polarizer utilizing a technique known as the “Spread-Squeeze” polarizer, which offers the advantages of compact size, ease of manufacture, and lower loss and noise figure, relative to the current technology that often employs an external 3-dB hybrid combiner. Ansys High Frequency Structure Simulator (HFSS), a commercial electromagnetic modeling and simulation tool, is used for the simulations. Further, this thesis aims to characterize the performance of the dual feed hornwith respect to aperture efficiency, that is, the degree to which the feed horn illuminates the parabolic reflector.

This dissertation consists of four parts: design of antenna in lossy media, analysisof wire antennas using electric field integral equation (EFIE) and wavelets, modeling and measurement of grounded waveguide coplanar waveguide (GCPW) for automotive radar, and E-Band 3-D printed antenna and measurement using VNA. In the first part, the antenna is modeled and simulated in lossy media. First, the vector wave functions is solved in the fundamental mode. Next the energy flow velocity is plotted to show near-field energy distribution for both TM and TE in air and seawater environment. Finally the power relation in seawater is derived to calculate the source dipole moment and required power. In the second part, the current distribution on the antenna is derived by solving EFIE with moment of methods (MoM). Both triangle and Coifman wavelet (Coiflet) are used as basis and weight functions. Then Input impedance of the antenna is computed and results are compared with traditional sinusoid current distribution assumption. Finally the input impedance of designed antenna is computed and matching network is designed and show resonant at designed frequency. In the third part, GCPW is modeled and measured in E-band. Laboratory measurements are conducted in 75 to 84 GHz. The original system is embedded with error boxes due to misalignment and needed to be de-embedded. Then the measurement data is processed and the results is compared with raw data. In the fourth part, the horn antennas and slotted waveguide array antenna (SWA) are designed for automotive radar in 75GHz to 78GHz. The horn antennas are fabricated using 3D printing of ABS material, and electro-plating with copper. The analytic solution and HFSS simulation show good agreement with measurement.

Modern communication systems call for state-of-the-art links that offer almost idealistic performance. This requirement had pushed the technological world to pursue communication in frequency bands that were almost incomprehensible back when the first series of cordless cellphones were invented. These requirements have impacted everything from civilian requirements, space, medical diagnostics to defense technologies and have ushered in a new era of advancements. This work presents a new and novel approach towards improving the conventional phased array systems. The Intelligent Phase Shifter (IPS) offers phase tracking and discrimination solutions that currently plague High-Frequency wireless systems. The proposed system is implemented on (CMOS) process node to better scalability and reduce the overall power dissipated. A tracking system can discern Radio Frequency (RF) Signals’ phase characteristics using a double-balanced mixer. A locally generated reference signal is then matched to the phase of the incoming receiver using a fully modular yet continuous complete 360ᵒ phase shifter that alters the phase of the local reference and matches the phase with that of an incoming RF reference. The tracking is generally two control voltages that carry In-phase and Quadrature-phase information. These control signals offer the capability of controlling similar devices when placed in an array and eliminating any ambiguity that might occur due to in-band interference.

This thesis is done as an extension of the development of an electrical engineering capstone project. The goal of the capstone is to create a system that can receive a 2.4 GHz Wi-Fi signal out to a range of 300 meters and then use it to point in the direction of a given Wi-Fi source. The design process of the capstone system is described in depth and the results of the proposed design are presented. The thesis work explores how this system can achieve a dual band capability at both 2.4 GHz and 5 GHz Wi-Fi bands. So, a slotted patch antenna system with a slotted ground plane was designed and tested and proved to deliver the ideal characteristics for accurate signal tracking.

This research presents advances in time-synchronized phasor (i.e.,synchrophasor) estimation and imaging with very-low-frequency electric fields. Phasor measurement units measure and track dynamic systems, often power systems, using synchrophasor estimation algorithms. Two improvements to subspace-based synchrophasor estimation algorithms are shown. The first improvement is a dynamic thresholding method for accurately determining the signal subspace when using the estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithm. This improvement facilitates accurate ESPRIT-based frequency estimates of both the nominal system frequency and the frequencies of interfering signals such as harmonics or out-of-band interference signals. Proper frequency estimation of all signals present in measurement data allows for accurate least squares estimates of synchrophasors for the nominal system frequency. By including the effects of clutter signals in the synchrophasor estimate, interference from clutter signals can be excluded. The result is near-flat estimation error during nominal system frequency changes, the presence of harmonic distortion, and out-of-band interference. The second improvement reduces the computational burden of the ESPRIT frequency estimation step by showing that an optimized Eigenvalue decomposition of the measurement data can be used instead of a singular value decomposition. This research also explores a deep-learning-based inversion method for imaging objects with a uniform electric field and a 2D planar D-dot array. Using electric fields as an illumination source has seen multiple applications ranging from medical imaging to mineral deposit detection. It is shown that a planar D-dot array and deep neural network can reconstruct the electrical properties of randomized objects. A 16000-sample dataset of objects comprised of a three-by-three grid of randomized dielectric constants was generated to train a deep neural network for predicting these dielectric constants from measured field distortions. Increasingly complex imaging environments are simulated, ranging from objects in free space to objects placed in a physical cage designed to produce uniform electric fields. Finally, this research relaxes the uniform electric field constraint, showing that the volume of an opaque container can be imaged with a copper tube antenna and a 1x4 array of D-dot sensors. Real world experimental results show that it is possible to image buckets of water (targets) within a plastic shed These experiments explore the detectability of targets as a function of target placement within the shed.

This work focuses on the analysis and design of large-scale millimeter-wave andterahertz (mmWave/THz) beamforming apertures (e.g., reconfigurable reflective surfaces– RRSs). As such, the small wavelengths and ample bandwidths of these frequencies enable the development of high-spatial-resolution imaging and high-throughput wireless communication systems that leverage electrically large apertures to form high-gain steerable beams. For the rigorous evaluation of these systems’ performance in realistic application scenarios, full-wave simulations are needed to capture all the exhibited electromagnetic phenomena. However, the small wavelengths of mmWave/THz bands lead to enormous meshes in conventional full-wave simulators. Thus, a novel numerical decomposition technique is presented, which decomposes the full-wave models in smaller domains with less meshed elements, enabling their computationally efficient analysis. Thereafter, this method is leveraged to study a novel radar configuration that employs a rotating linear antenna with beam steering capabilities to form 3D images. This imaging process requires fewer elements to carry out high-spatial-resolution imaging compared to traditional 2D phased arrays, constituting a perfect candidate in low-profile, low-cost applications. Afterward, a high-yield nanofabrication technique for mmWave/THz graphene switches is presented. The measured graphene sheet impedances are incorporated into equivalent circuit models of coplanar switches to identify the optimum mmWave/THz switch topology that would enable the development of large-scale RRSs.ii Thereon, the process of integrating the optimized graphene switches into largescale mmWave/THz RRSs is detailed. The resulting RRSs enable dynamic beam steering achieving 4-bits of phase quantization –for the first time in the known literature– eliminating the parasitic lobes and increasing the aperture efficiency. Furthermore, the devised multi-bit configurations use a single switch-per-bit topology retaining low system complexity and RF losses. Finally, single-bit RRSs are modified to offer single-lobe patterns by employing a surface randomization technique. This approach allows for the use of low-complexity single-bit configurations to suppress the undesired quantization lobes without residing to the use of sophisticated multi-bit topologies. The presented concepts pave the road toward the implementation and proliferation of large-scale reconfigurable beamforming apertures that can serve both as mmWave/THz imagers and as relays or base stations in future wireless communication applications.

This thesis presents three novel studies. The first two works focus on galvanically isolated chip-to-chip communication, and the third research studies class-E pulse-width modulated power amplifiers. First, a common-mode resilient CMOS (complementary metal-oxide-semiconductor) galvanically isolated Radio Frequency (RF) chip-to-chip communication system is presented utilizing laterally resonant coupled circuits to increases maximum common-mode transient immunity and the isolation capability of galvanic isolators in a low-cost standard CMOS solution beyond the limits provided from the vertical coupling. The design provides the highest reported CMTI (common-mode transient immunity) of more than 600 kV/µs, 5 kVpk isolation, and a chip area of 0.95 mm2. In the second work, a bi-directional ultra-wideband transformer-coupled galvanic isolator is reported for the first time. The proposed design merges the functionality of two isolated channels into one magnetically coupled communication, enabling up to 50% form-factor and assembly cost reduction while achieving a simultaneously robust and state-of-art performance. This work achieves simultaneous robust, wideband, and energy-efficient performance of 300 Mb/s data rate, isolation of 7.8 kVrms, and power consumption and propagation delay of 200 pJ/b and 5 ns, respectively, in only 0.8 mm2 area. The third works studies class-E pulse-width modulated (PWM) Power amplifiers (PAs). For the first time, it presents a design technique to significantly extend the Power back-off (PBO) dynamic range of PWM PAs over the prior art. A proof-of-concept watt-level class-E PA is designed using a GaN HEMT and exhibits more than 6dB dynamic range for a 50 to 30 percent duty cycle variation. Moreover, in this work, the effects of non-idealities on performance and design of class-E power amplifiers for variable supply on and pulse-width operations are characterized and studied, including the effect of non-linear parasitic capacitances and its exploitation for enhancement of average efficiency and self-heating effects in class-E SMPAs using a new over dry-ice measurement technique was presented for this first time. The non-ideality study allows for capturing a full view of the design requirement and considerations of class-E power amplifiers and provides a window to the phenomena that lead to a mismatch between the ideal and actual performance of class-E power amplifiers and their root causes.