The short wavelengths and wide available bandwidth in the terahertz (THz) regime make it an attractive frequency range for commercial, passive imaging applications. Fully exploiting these benefits requires low-cost THz imaging solutions with a high density of beams and excellent temperature sensitivity. Thanks to advancements in the temperature sensitivity of direct detectors integrated in processes such as CMOS and SiGe, commercially available silicon platforms have become the most promising candidates for a low-cost THz camera. Integrating these detectors in dense, large focal plane arrays (FPAs) operating over ultra-wide bandwidths would yield a camera capable of passive imaging with a diffraction-limited resolution. This thesis describes the design and characterization of arrays integrated in both CMOS and SiGe BiCMOS towards realizing such a passive THz camera.

To explore the realization of such a camera, we first extensively characterized a previously proposed chessboard FPA that was designed to achieve a near diffractionlimited resolution. This chessboard FPA was integrated with direct detectors based on Schottky diodes in 22-nm CMOS, and operates from 200 GHz to 600 GHz. Characterization was performed using an over-the-air measurement setup, enabling 2-D, multi-beam pattern characterization with a high dynamic range. Measurements of both the aperture efficiency and beam overlap between adjacent pixels demonstrated that the fabricated chessboard FPA improves gain at the edge-of-coverage by 1.2dB compared to an ideal hexagonal FPA of uniform feeds. The chessboard configuration therefore combines state-of-the-art focal plane sampling with minimal penalty in antenna efficiency.

Building on these results, we designed a quasi-optical system to validate the imaging performance of the CMOS-integrated FPA in a practical scenario. Since the Schottky diodes in the FPA did not enable passive imaging, active illumination of the sample was required to achieve sufficient imaging dynamic range. The quasi-optical system was optimized to ensure that the imaging resolution was dictated solely by the focal plane sampling in the chessboard FPA, while maintaining sufficient coupling between all pixels and the active source. Using this system, we performed an imaging demonstration of an ivy leaf hidden in an envelope, further emphasizing the state-of-the-art spatial resolution of the chessboard FPA.

While the CMOS-integrated chessboard FPA demonstrated excellent spatial resolution, its temperature sensitivity was insufficient for passive imaging. To overcome this limitation, we designed the chessboard FPA in a 130-nm SiGe BiCMOS process, utilizing heterojunction bipolar transistors (HBTs) to implement the direct detectors. The implemented chessboard FPA operates between 250 GHz – 600 GHz, and features detectors employing deeply saturated HBTs in a common-base configuration. The prototype was characterized using the quasi-optical system designed for the imaging demonstration. Measurements of the radiation patterns and responsivity showed good agreement with simulations, although the noise-equivalent power was higher than expected. Nevertheless, it is still competitive with the state-of-the-art and should enable passive THz imaging. The noise-equivalent temperature difference was estimated to be 1.6K for a 1 s integration time.

A critical challenge for passive THz cameras is low-frequency noise injected by the direct detectors. To address this, we proposed a solid-state chopper based on a reconfigurable periodic surface. The chopping operation is realized by electronically controlling the transmission through this surface, which is both more compact and faster than a mechanical chopping wheel, while preserving the spatial sampling of the chessboard FPA. The chopper was implemented in 130-nm SiGe BiCMOS and consists of sub-wavelength metal patches in a chessboard geometry loaded with varactor-connected MOSFETs. For characterization, a quasi-optical system was developed, consisting of two elliptical silicon lenses with the chopper located at the shared focus. Measurements showed that the chopper transmission was significantly lower than simulated. When using impedance measurements of a single MOSFET device to re-simulate the chopper, a considerably better match with simulations was obtained. To achieve the desired chopper performance, an alternative implementation was designed based on the measured impedance of an HBT-based load. Although this design has not yet been fabricated, simulations indicate it should enable passive imaging performance when combined with a state-of-the-art antenna-coupled direct detector. Since this design is based on device measurements, there is a high confidence that this proposed chopper design contributes towards the realization of a compact, passive THz camera with near diffraction-limited resolution.

Wireless Radio Frequency (RF) systems have revolutionized the way we transmit and receive information from mobile platforms. In recent decades, the number of applications relying on wireless technologies, including telecommunications, radar, and sensing, have exploded. RF engineers have pushed the technological boundaries to feed our appetite for more information through the wireless networks. However, congestion in the low-frequency radio spectrum means that applications are in a continuous battle to be as spectrally efficient in the frequency bands allocated to them. This strategy has worked well for many wireless generations, but has added considerable challenges due to increased system complexity and decaying energy efficiency.....

Two devices, a SiGe BiCMOS MOSFET and a SiGe HBT, were characterized through on-wafer measurements in the 220–500 GHz range. The results showed that the PDK model of the MOSFET did not accurately represent the device. Conventional open–short de-embedding was found to lose accuracy at sub-THz frequencies due to its inherent lumped-element approximation. To address this limitation, an improved de-embedding method was developed by estimating a correction matrix A′ using transmission-line equivalent circuits, achieving up to 15.6 dB improvement in S11 and S22 for an HBT interconnect in simulation compared to the classical approach. The characterized MOSFET was used to simulate the integrated chopper transmissivity, which closely matched over-the-air measurements. The HBT characterization showed better agreement with the PDK, but the higher characterized capacitance resulted in reduced chopper performance.

This work addresses the limitations of conventional high-frequency methods in the modeling of lens antennas. While these structures are commonly analyzed using efficient Geometrical Optics (GO) / Physical Optics (PO) techniques, such approaches present significant limitations when the shadow region -defined as the surface area illuminated at incidence angles above the critical angle- is strongly illuminated, or when multilayer stratifications are incorporated. Furthermore, the full-wave validation is computationally intensive for medium-sized lenses, and impractical for electrically-large designs, leaving designers overly reliant on traditional methods and lacking detailed electromagnetic insight.

Firstly, to address the computational challenges with full-wave simulation of large lens designs, an approach based on PPW-embedding (Parallel-Plate Waveguide embedding) of the principal lens sections is followed. This reduction in problem size enables feasible full-wave simulations while also yielding valuable qualitative insights into the lens performance.

Secondly, to overcome the GO-PO limitations in predicting fields beyond the critical angle of incidence, this work follows a rigorous surface field modeling approach based on the Stratified-media Spectral Green’s Function, applied to locally flat surface approximations and evaluated using Inverse Fourier Transform in Steepest Descent Path (SDP) integration. The proposed method shows strong agreement with full-wave simulations and offers deeper insight into surface fields under critical-angle illumination, revealing their impact on radiation performance and enabling more effective lens designs.

Finally, the spectral approach is extended to the analysis of matching layers on the surfaces of high-permittivity lenses, demonstrating greater reliability than GO-PO techniques while maintaining computational efficiency superior to full-wave simulations. This study offers spectral-domain insight into surface lens phenomena and evaluates the performance enhancements provided by anti-reflection coatings.

Automated Robotic arms redefine the limits of antenna characterization. This paper presents a method to estimate the far-field radiation pattern of antennas utilizing near-field measurements through the use of a 6-axis robotic arm. The innovation of our project lies in overcoming the current limitation of fixed scanning geometries, by extending them to any possible spatial shape with the support of a 6-axis robotic arm.
The project is built and validated incrementally through a series of MATLAB functions, utilizing the equivalence theorem as a NF to FF transformation method. Each stage builds upon the previous ones and increases in complexity. Validation stages begin by simulating infinitesimal dipoles and progress up to experimental validation of a tilted horn antenna. All the validation steps are successfully met, except for an unexpected phase symmetry. Our work sets a solid foundation for further development of this antenna measurement system. The system will significantly improve antenna characterization by enabling more flexible scanning grids.

This thesis explores the automation of near-field region and far-field region antenna measurements using a 6 degrees of freedom robotic arm. A path planning algorithm is developed to detect and minimize motion discontinuities ("jumps") by evaluating joint movements through a cost function. An inverse kinematics method is used to find all possible joint configurations, allowing for smoother path plannings for the measurements. Various sorting algorithms are developed and tested on both planar and spherical grids to determine the most efficient measurement paths in terms of path smoothness. Furthermore, the optimum placement of the antenna under test is studied using the above-mentioned method, to ensure path feasibility while minimizing the strain on the probe cable. Experimental validation is performed in MATLAB, commercial simulation software RoboDK and on the physical robotic arm. The results confirm that the proposed algorithms successfully reduce joint jumps and cable strain, enabling accurate and automated antenna measurements in both NF and FF configurations.

Accurately characterizing antenna radiation patterns in the millimetre-wave (mmW) frequency range presents significant challenges due to the short wavelengths involved. A measurement system that incorporates a 6-axis robotic arm is implemented to gain more positional control over the antenna measurement. This thesis presents the software to control the system, including the robotic arm and a Vector Network Analyser, in a user-friendly manner. Additionally, it dives into the influence of the characteristics and movement of the robotic arm on the setup. To ensure reliability and maintainability of the codebase, the software was structured using several objects and data classes, each responsible for a specific part of the system. Tests of the system showed a solid foundation of the graphical user interface and the back-end software architecture. Analysis of the repeatability of the system revealed that results may deviate by magnitude differences of 0.8 dB and phase differences up to 30°. Compared to a calibrated position of the system, displacements in individual joints led to significant phase difference of up to 20°. There was no correlation found in deviations of magnitude or phase response and the settle time between the movements of the robot and the measuring of the VNA.

This thesis presents the design and performance evaluation of electronically steered phased lens arrays operating at 140 GHz for high resolution sensing applications. The primary objective of the thesis is to design and analyze lens phased arrays fed by an array of leaky-wave antenna elements achieving 1 degree resolution, while having 20 degree field of view, 30dB single lens directivity and 70% spillover efficiency. Bi-directional ray-tracing approach is used to calculate the required weights for single lens beam steering together with GO/PO methods. Key parameters such as directivity, gain, spillover efficiency and maximum side lobe level are optimized using a graphical method called 'Two dimensional sweeps'. The results obtained using the proposed methods have been validated using full wave simulations.

This work aims to build a measurement test bench for wideband mixer EVM characterization at sub-terahertz frequencies. A VNA based setups with two frequency extenders are implemented. While one of the VNA sources can be used as the LO input, the other source will be swept over a frequency grid so that the RF output of the mixer under test will be down converted and read out tone by tone. Then the modulated signals are expected be reconstructed from the frequency domain measurement result, which will be demodulated for EVM characterization. A two-tier calibration method is used to extract the absolute power from the target RF channel. The key performance of the mixer under test, such as conversion loss, image rejection ratio and linearity are measured over an IF bandwidth up to 4GHz. Nevertheless, the major challenge for VNA based EVM measurements are the unhandled phase between the two sources of VNA, preventing the system to reconstruct a stable time domain signal. To solve this problem, an auxiliary phase channel setup is proposed, which can carry the unhandled phase information from one of the VNA source, thus providing a stable phase measurement for EVM measurements. To validate the proposed setups, the adjusted phase is derived from measurement results of the MUT channel and the results from the auxiliary channel. A phase stability of $\pm$5 degrees can be achieved with the proposed setups. Finally, EVM characterization is performed based on the proposed setup. A EVM floor of -30dB is achieved with a 300MHz QPSK signal, the error due to thermal noise is reduced due to the narrow band receiver of the VNA.

In the framework of this MSc thesis the analysis of core-shell leaky-wave lens antennas is presented, based on a combination of asymptotic and Physical Optics techniques. This study aims to develop an analysis approach which can be subsequently used for the optimization of the Fly’s Eye antenna concept, through enabling the investigation of shaped variations of the core lens. The main difficulty of this prospect refers to the surface of the core lens being in the near field of the leaky wave feeding structure, since the evaluation of the near field is in general a computationally inefficient process. Adhering to this conclusion, a big part of this thesis elaborates on a very fast approach for the derivation of the near field, through asymptotically approximating the involved integral expressions. More specifically, the presented method exploits the nature of the near field in the examined stratification through introducing an approximation in the integral expressions, which in turn enables their asymptotic evaluation in a straightforward manner. Subsequently, the near field on the core lens is combined with a set of Physical Optics techniques in order to develop a model for the integrated lens architecture of the Fly’s Eye antenna. Modelling the core-shell structure in such a manner enables its study in a much more computationally efficient fashion compared to the use of a full-wave simulator. In addition, it facilitates the investigation of structural alterations in the antenna concept, like shaped variations of the core lens. The derived model presented in this thesis also contributed to the measurement campaign of the Fly’s Eye antenna prototype, through identifying a problematic component in the assembled prototype.

In the framework of this MSc thesis, the analysis and design guidelines for part of the quasi-optical system of a proposed astronomical instrument, called TIFUUN, are presented. The TIFUUN instrument is an imaging spectrometer, planned to be placed in the ASTE telescope to perform ground-based astronomical observations in the mm-submm wavelength regime. Part of the instrument development involves the design of the quasi-optical system coupling the radiation from the telescope’s main dish to the spectrometer array. In this thesis, the focal plane array of antennas, as well as the first component of the quasi-optical chain are analyzed and two different design approaches are presented, as candidate geometries. Each of them satisfies the requirements of different science surveys targeted by TIFUUN. The first examined architecture is comprised of a focal plane array of on-chip feeding elements under a single hyper-hemispherical lens, which is then coupled geometrically to a hyperbolic lens. The second geometry is instead comprised of an array of integrated elliptical lenses, with a single on-chip feeding element per lens, diffractively coupled to a hyperbolic lens. The methodologies to efficiently analyze these kinds of geometries are Geometrical Optics (GO) combined with analysis in reception for the first design approach and Coherent Fourier Optics (CFO) for the second one. During the design process, the performance of both architectures is optimized throughout the field of view, using methodologies to correct for phase aberrations, such as feed displacement inside the lenses and symmetric shaping of dielectric surfaces. The design guidelines provided and insights obtained during this MSc project will be utilized to develop the quasi-optical system of the TIFUUN instrument, within the limited space of its cryostat.

Recently, there has been an increasing demand for security in public places. As a result, non-destructive and fast millimetre-wave and submillimetre-wave imaging systems have gained more and more attention.
This project is based on Concealed Objects Stand-off Real-Time Imaging for Security (CONSORTIS), which is a European next-generation airport security imaging radar system published in 2017. In this project, we will discuss the design of the lens antenna illuminated by a leaky wave waveguide antenna for a large format focal plane array with wide scanning capabilities in three typical cases. The Coherent Fourier Optics (CFO) and leaky wave antenna design methodologies are used in this project. The system will be analysed in reception mode and then validated in transmission mode. We have a very promising performance with an aperture efficiency of about 80% in the centre and 47% at the edge of the array with a shaped top and AR coating. The directivity of the antenna at the edge is about 50.2 dB. And the scan loss is about -2.3 dB, which means it can scan about 10,000 beams in total.

This master thesis explores the capacity of MIMO arrays for communication in the radiative near field through antenna design. This research applies an in-house MATLAB model based on free space Green’s function to calculate the channel matrix, revealing the potential increase of capacity through the use of incoherent arrays with directive antennas in the incoherent range without the need for interference cancellation.

The optimization of the equivalent aperture current and the design of lens antennas are the key points in realizing the ultimate goal of maximizing the capacity between antenna arrays. The accuracy of the channel matrix from the MATLAB model and the performance of the designed lens antennas are validated through full-wave simulation using CST. Furthermore, the internal reflections between the arrays are studied, offering solutions to mitigate the effects of the reflections for future array designs.

This work serves as a feasibility study, providing sufficient confidence in the application of communication systems in the radiative near field without the need for signal processing (e.g. interference cancellation, multi-path cancellation, etc.). Furthermore, the methodology in this thesis offers insights for future antenna designs for different applications. In summary, this study proposes and validates a potential solution for the design of next-generation communication systems.

This work demonstrates the imaging of (near) diffraction-limited images in the THz domain using a CMOS integrated camera. A Quasi Optical Setup is fabricated, aligned the radiation patterns and losses are characterized.

Front-end Monolithic Microwave Integrated Circuits (MMICs) have recently become commercially available for frequencies above 100 GHz. However, achieving low-loss and broadband interconnections between the antenna and MMICs is challenging for integrated front ends at these frequencies. This thesis presents the characterization of a flip-chip interconnection used for an integrated front end at 150 GHz (G-band) with an on-package leaky-wave dual lens antenna. Two paths for the front-end integration have been proposed. The first path adopts CPW transmission lines on 500 μm-thick fused silica and provides easy assembly and seamless flip-chip capabilities. The second uses microstrip transmission lines on 50 μm-thick fused silica and provides lower transmission line loss but a challenging assembly and flip-chip interconnection. In this thesis, a path toward microstrip and CPW flip-chip interconnections has been outlined at the high millimeter-wave frequencies. Two-port test structures using CPW transmission lines were developed, adopting a double Thru-Reflect-Line calibration and allowing for accurate extracting of the interconnection response. The final interconnection to the MMICs has been realized using a via-less CPW to microstrip transition with high impedance transmission line S11 matching compensation. The simulated S11 and S22 are below -12 dB, Ohmic loss below 0.6 dB, radiation loss below 0.4 dB, and transmission line losses around 0.15 dB/mm.

Within the framework of this thesis, the analysis of the infinite slot leaky wave antenna is presented and a new geometry for the feed of a leaky lens is explored. Firstly, the analysis of the propagating leaky wave modes (TM0 and slot modes) is done leading to the findings about the location of the slot pole w.r.t. k0, as well as the contributions of the leaky waves and how they behave when the thickness of air-cavity and width of the slot change. Secondly, the spectral analysis of the near field is put forward with the goal of gaining deeper understanding of the leaky wave modes’ behaviour and their asymmetry. Finally, a new geometry: leaky wave antenna with multiple slots is explored and its potential of lowering the levels of cross pol. is shown.

In this thesis, an efficient optimization method is described for synthesizing lens antennas fabricated in low permittivity plastic materials to achieve wide scanning performances. The method is based on an antenna in reception representation. The optimized parameters are the location and orientation of the antenna feeder, lens angular region and its shape by adding Zernike polynomials to standard ellipsoidal shape. The synthesized lens antennas achieve scan losses lower than 3dB while scanning up to 60°. The presented theoretical results are validated using full wave simulations. Furthermore, an efficient analysis method based on Geometrical Optics and ray tracing is developed. This method is applied to the study of multi lens Quasi-Optical structures. The presented theoretical results are validated by multi surface Physical-Optics approach.

Photoconductive antennas (PCAs) are an interesting candidate for imaging systems due to their relatively low cost and ability to provide a bandwidth of hundreds of GHz. The large bandwidth of PCAs allows for sub-millimeter depth resolution. However, the often-used single-element PCAs are intrinsically limited in the amount of power they can radiate due to several saturation effects. To increase the radiated power, array-based PCAs have been introduced by the scientific community. In the first part of this work, the impact of adding a leaky wave cavity to a lens-coupled Photoconductive Connected Array (PCCA) is studied. The fields radiated by the lens are found using a Physical Optics method, and the effect of the lens on the energy spectra of the radiated fields is quantified. Measurements of two fabricated PCCA geometries are compared with simulations. In the second part of this work, an imaging setup is designed to benchmark several state-of-the-art PCAs. Subsequently, the coupling between two PCAs in an imaging setup is studied via a field-matching formalism.

Millimeter- and submillimeter wave applications, such as point-to-point wireless communications in beyond-5G scenarios, long-range automotive radars and astronomy and astrophysics science cases from space require antennas with high-gain beams that are steerable. At lower (microwave) frequencies, fully sampled phased arrays with thousands of elements have been demonstrated for this purpose. However, above roughly 100 GHz, integrated-circuit technology faces major bottlenecks in terms of size, power efficiency, thermal management and technological immaturity. Consequently, only integrated phased arrays with very few elements have been reported in the literature above 100 GHz. To still achieve the gain and enable beam scanning, mechanically actuated reflectors are now typically employed. However, such solutions are bulky, power-hungry and do not allow rapid beam steering. To overcome these limitations, we propose, analyze, design, fabricate and demonstrate a new antenna architecture in this thesis: the scanning lens phased array. The scanning lens phased array is a compact, low-power and very sparse array of integrated lens antennas that we demonstrate with scanning capabilities up to 25 degrees around broadside. A hybrid electro-mechanical approach to beam steering is employed: the array factor is scanned electronically and the element patterns are steered mechanically. The grating lobes that arise in the array factor due to the array’s sparsity are suppressed by the high directivity of the lens elements. This results in a clean, highgain beam towards the desired scan angle...

Lens array architectures are being developed for high frequency applications such as phased arrays for 5G point-to-point communications, Fly’s Eye lens arrays for wideband wireless communications and scanning phased arrays at sub-millimeter wavelengths. Each of these applications employ different feed configurations, lens geometries and require specific feed isolation levels. In these architectures, the mutual coupling between feeds is an important design criteria. This project proposes a theoretical model based on Geometrical Optics and Physical Optics to represent the multiple reflections in a dielectric lens antenna and its impact on the mutual coupling between lens feeders. This model is then employed to study the mutual coupling in architectures with different feed models, edge illumination levels, feed positions, lens diameters and dielectric materials.