Millimeter astronomy unlocks a window to the earliest produced light in the universe, called the Cosmic Microwave Background (CMB). Through analysis of the CMB, overarching features about the universe's evolution and structure can be better understood. Modern millimeter-wave instruments are constantly seeking improvements to sensitivity in the effort to further constrain small CMB anisotropies in both temperature and polarization. As a result, detailed investigations into lesser-known processes of the universe are now becoming possible. Here I present work on the millimeter-wavelength analysis of z ≈ 1 quiescent galaxy samples, whose conspicuous quenching of star formation is likely the result of active galactic nuclei (AGN) accretion onto supermassive black holes. Such AGN feedback would heat up a galaxy's surrounding circumgalactic medium (CGM). Obscured by signal from cold dust, I isolate the thermal Sunyaev-Zel'dovich effect, a CMB temperature anisotropy produced by hot ionized gas, to measure the CGM's average thermal energy and differentiate between AGN accretion models. I find a median thermal energy that best corresponds with moderate to high levels of AGN feedback. In addition, the radial profile of cold dust associated with the galaxy samples appears to be consistent with large-scale clustering of the universe. In the endeavor of increasingly efficient millimeter-wave detectors, I also describe the design process for novel multichroic dual-polarization antennas. Paired with extended hemispherical lenslets, simulations of these superconducting antennas show the potential to match or exceed performance compared to similar designs already in use. A prototype detector array, with dual-bowtie and hybrid trapezoidal antennas coupled to microwave kinetic inductance detectors (MKIDs) has been made and is under preparation to be tested in the near future. Finally, I also present my contributions to the cryogenic readout design of the Ali CMB Polarization Telescope (AliCPT), a large-scale CMB telescope geared towards searching the Northern Hemisphere sky for a unique `B-mode' polarization expected to be produced by primordial gravitational waves. Cryogenic readout is responsible for successful interfacing between room temperature electronics and sensitive detectors operating on AliCPT's sub-Kelvin temperature focal plane. The development of millimeter-wave instruments and future endeavors show great potential for the overall scientific community.

I present a trade-study of methods for a 1-port vacuum cryogenic in-situ calibration of a vector network analyzer. The three main methods I investigated in this work were: calibration using a commercial off the shelf latching electro-mechanical six way switch, a custom switch board, and a flexible multi channel stripline based printed circuit board. The test procedure was developed for use in a ground based closed-cycle cryogenic test bench to measure the reflection coefficient of a single port connectorized device under test. The device was installed in the cryogenic system alongside calibration standards. The goal of the trade study was to find which method could be used to accomplish calibration and device measurement in a single thermal cycle. Four cycles were required for industry standard open-short-load device calibration. Room temperature measurements were done with all three calibration schemes but ultimately only the single pole six throw switch proved effective enough for further testing. The cryogenic testing was carried out on an arbitrary device at ∼ 3K temperature, over a 6 GHz bandwidth. The final objective was to develop a setup and procedure for measuring the frequency and temperature dependent complex impedance of superconducting devices such as hot electron bolometer mixers, which are used for down converting the signal in the IF chain of astronomy instruments. Characterization of superconducting devices while they are at their operating temperature is challenging using traditional calibration methods. This commercial alternative is less expensive and more efficient in terms of thermal cycles and set up because it can be installed in a wide variety of cyrogenic systems.

Studying the interstellar medium (ISM) is the key to answering questions about how material that exists between the stars drives the evolution of galaxies. Current models for the ISM life-cycle exist, but several steps lack observational evidence. Inthis dissertation I present the work I completed in support of up-coming mission to further study the ISM. This work includes ancillary data analysis of the Carina Nebula for the upcoming balloon mission: astrophysics stratospheric telescope for high spectral resolution observations at submillimeter wavelengths (ASTHROS). I present a derived molecular gas map of Carina from Herschel dust continuum emission maps at wavelengths between 70-500 microns. I compare it to the distribution of atomic gas, using HI 21 cm data, and of multiple CO isotopologues for the J = 1 → 0 rotational transition. I use these data sets to separate the CO–dark and CO–bright molecular components to study their relative contribution to the total molecular gas mass budget in Carina. I studied the transition between atomic and molecular gas in this region, by deriving the molecular fraction as a function of position, and comparing it to theoretical models of this transition. I also present the flight hardware design, testing, and space qualification of the intermediate frequency (IF) harness for the galactic/extragalactic ultra long duration balloon spectroscopic terahertz observatory (GUSTO). The harness transmits signal via novel cryogenic flexible stripline based transmission lines operating from 0.3 - 6.0 GHz. I designed three sets of 8-channel ribbons with characteristic insertion loss of 3.07 dB/ft at 5 GHz while the line was at a temperature gradient between 20 K - 300 K. Missions like GUSTO make use of non-linear mixing elements to achieve down-conversion of higher frequencies into IF bands. The mixers have a temperature dependent impedance that is difficult to measure. The last chapters of this work detail my attempt to carry out in-situ vacuum cryogenic calibrations using industry standard commercial off-the-shelf calibration kits and cryogenic RF electro-mechanical latching switches. I present the complex impedance of a non-linear superconducting transmission line as measured with a cryogenic calibration.

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 recent trends in wireless communication, fueled by the demand for lower latency and higher bandwidth, have caused the migration of users from lower frequencies to higher frequencies, i.e., from 2.5GHz to millimeter wave. However, the migration to higher frequencies has its challenges. The sensitivity to blockages is a key challenge for millimeter wave and terahertz networks in 5G and beyond. Since these networks mainly rely on line-of-sight (LOS) links, sudden link blockages highly threaten the reliability of such networks. Further, when the LOS link is blocked, the network typically needs to hand off the user to another LOS basestation, which may incur critical time latency, especially if a search over a large codebook of narrow beams is needed. A promising way to tackle the reliability and latency challenges lies in enabling proaction in wireless networks. Proaction allows the network to anticipate future blockages, especially dynamic blockages, and initiate user hand-off beforehand. This thesis presents a complete machine learning framework for enabling proaction in wireless networks relying on the multi-modal 3D LiDAR(Light Detection and Ranging) point cloud and position data. In particular, the paper proposes a sensing-aided wireless communication solution that utilizes bimodal machine learning to predict the user link status. This is mainly achieved via a deep learning algorithm that learns from LiDAR point-cloud and position data to distinguish between LOS and NLOS(non line-of-sight) links. The algorithm is evaluated on the multi-modal wireless Communication Dataset DeepSense6G dataset. It is a time-synchronized collection of data from various sensors such as millimeter wave power, position, camera, radar, and LiDAR. Experimental results indicate that the algorithm can accurately predict link status with 87% accuracy. This highlights a promising direction for enabling high reliability and low latency in future wireless networks.

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.

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.