In this dissertation, enhanced coherent detection of terahertz (THz) radiation is presented for Silicon integrated circuits (ICs). In general THz receivers implemented in silicon technologies face a challenge due to the high noise figure (NF) of the low noise amplifier (LNA) and low conversion gain of the radio frequency (RF) mixers. Moreover, issues with implementing local oscillators (LOs) further compound these challenges, including power driving mixes, distribution networks, and overall power consumption, particularly for large-scale arrays. To address these inherent obstacles, two notable cases of enhancing THz receiver performance are presented. In the Sideband Separation Receiver (SSR) for space-borne applications is introduced. Implemented in SiGe BiCMOS technology this broadband SSR boasts a high Image Rejection Ratio (IRR) exceeding 20 dB across 220 – 320 GHz. Employing a modified Weaver architecture, optimized for simultaneous spectral line observation, it utilizes an I/Q double down-conversion, pushing the technological boundaries of silicon and enabling large-scale focal plane array (FPA) deployment in space. Notably, the use of a sub-harmonic down-conversion mixer (SHM) significantly reduces LO power generation challenges, enhancing scalability while maintaining minimal NF. In the 4x4 FPA active THz imager, a dual-polarized patch antenna operating at 420 GHz utilizes orthogonal polarization for RF and LO signals, coupled with a coherent homodyne power detector. Realized in 0.13µm SiGe HBT technology, the power detector is co-designing with the antenna to ensure minimal crosstalk and achieving -30dB cross-polarization isolation. Illumination of the LO enhances power detector performance without on-chip routing complexities, enabling scalability to 1K pixel THz imagers. Each pixel achieves a Noise-Equivalent Power (NEP) of 1 pW/√Hz at 420 GHz, and integration with a readout and digital filter ensures high dynamic range. Furthermore, this study explores radiation hardening techniques to mitigate single-event effects (SEEs) in high-frequency receivers operating in space. Leveraging a W-band receiver in 90 nm SiGe BiCMOS technology, matching considerations and diverse modes of operation are employed to reduce SEE susceptibility. Transient current pulse modeling, validated through TCAD simulations, demonstrates the effectiveness of proposed techniques in substantially mitigating SETs within the proposed radiation-hardened-by-design (RHBD) receiver front-end.

Kinetic Inductance Detectors (KIDs) offer highly sensitive solutions for millimeter and submillimeter wave astronomy. KIDs are superconducting detectors capable of measuring photon energy and arrival time. KIDs use the change in surface impedance of the superconductor when an incident photon is absorbed and breaks Cooper pairs in the superconducting material. This occurs when KIDs use a superconducting resonator: when a photon is incident on the inductor, the photon is absorbed and inductance increases and the resonant frequency decreases. The resonator is weakly coupled to a transmission line which naturally allows for multiplexing to allow up to thousands of detectors to be read out on one transmission line. In this thesis a KID is presented to be used at submillimeter wavelengths. I optimized a polarization-sensitive aluminum absorber for future Balloon-borne Large Aperture Submillimeter Telescope (BLAST) missions. BLAST is designed to investigate polarized interstellar dust and the role of magnetic fields on star formation. As part of the effort to develop aluminum KIDs for BLAST, I investigated the optical coupling method including different feedhorn structures and a hybrid design. I present a suite of simulations calculating the absorption efficiency of the absorber. The optimized KID is a feedhorn/waveguide coupled front-illuminated detector that achieves 70% absorption over the frequency band centered at 250um.

The Discrete Fourier Transform (DFT) is a mathematical operation utilized in various signal processing applications including Astronomy and digital communications (satellite, cellphone, radar, etc.) to separate signals at different frequencies. Performing DFT on a signal by itself suffers from inter-channel leakage. For an ultrasensitive application like radio astronomy, it is important to minimize frequency sidelobes. To achieve this, the Polyphase Filterbank (PFB) technique is used which modifies the bin-response of the DFT to a rectangular function and suppresses out-of-band crosstalk. This helps achieve the Signal-to-Noise Ratio (SNR) required for astronomy measurements. In practice, 2N DFT can be efficiently implemented on Digital Signal Processing (DSP) hardware by the popular Fast Fourier Transform (FFT) algorithm. Hence, 2N tap-filters are commonly used in the Filterbank stage before the FFT. At present, Field Programmable Gate Arrays (FPGAs) and Application Specific Integrated Circuits (ASICs) from different vendors (e.g. Xilinx, Altera, Microsemi, etc.) are available which offer high performance. Xilinx Radio-Frequency System-on-Chip (RFSoC) is the latest kind of such a platform offering Radio-frequency (RF) signal capture / generate capability on the same chip. This thesis describes the characterization of the Analog-to-Digital Converter (ADC) available on the Xilinx ZCU111 RFSoC platform, detailed design steps of a Critically-Sampled PFB, and the testing and debugging of a Weighted OverLap and Add (WOLA) PFB to examine the feasibility of implementation on custom ASICs for future space missions. The design and testing of an analog Printed Circuit Board (PCB) circuit for biasing cryogenic detectors and readout components are also presented here.

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.

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.

Advancements in technologies like the Internet of thing causes an increase in the presence of wireless transceivers. A cooperative communication between these transceivers opens a doorway for multiple novel applications. A mobile distributed transceiver architecture is a much more dynamic environment dictating the necessity of faster synchronization among the transceivers. A possibility of simultaneous synchronization in parallel with the communication will theoretically ensure a high-speed synchronization without affecting the data rate. One such system has been implemented using a Costas loop and an extension of such synchronization technique to the full-duplex model has also been addressed. The rise in spectral demand is hard to meet with the regular Time duplex and frequency duplex communication systems. A full-duplex system is theoretically expected to double the spectral efficiency. However it comes with tremendous challenges, This thesis works on one of those challenges in implementing full-duplex synchronization. A coherent full-duplex model is designed to overcome the issue of transmitter leakage modeled as injection pulling, A known solution for this effect has been used to resolve the issue and complete the coherent full-duplex model. This establishes the simultaneous synchronization and communication system.

The objective of this work is to design a novel method for imaging targets and scenes which are not directly visible to the observer. The unique scattering properties of terahertz (THz) waves can turn most building surfaces into mirrors, thus allowing someone to see around corners and various occlusions. In the visible regime, most surfaces are very rough compared to the wavelength. As a result, the spatial coherency of reflected signals is lost, and the geometry of the objects where the light bounced on cannot be retrieved. Interestingly, the roughness of most surfaces is comparable to the wavelengths at lower frequencies (100 GHz – 10 THz) without significantly disturbing the wavefront of the scattered signals, behaving approximately as mirrors. Additionally, this electrically small roughness is beneficial because it can be used by the THz imaging system to locate the pose (location and orientation) of the mirror surfaces, thus enabling the reconstruction of both line-of-sight (LoS) and non-line-of-sight (NLoS) objects.

Back-propagation imaging methods are modified to reconstruct the image of the 2-D scenario (range, cross-range). The reflected signal from the target is collected using a SAR (Synthetic Aperture Radar) set-up in a lab environment. This imaging technique is verified using both full-wave 3-D numerical analysis models and lab experiments.

The novel imaging approach of non-line-of-sight-imaging could enable novel applications in rescue and surveillance missions, highly accurate localization methods, and improve channel estimation in mmWave and sub-mmWave wireless communication systems.