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.

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.

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.

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...@en

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.

The objective of the project is to design a system which can control the temperature of a va-porizing liquid microthruster (VLM). The liquid in a VLM is heated using a heater resistor.This resistor will be used to both heat the liquid and measure the temperature.In this thesis the subsystem responsible for the measurements and the conversion of the mea-sured signals to the digital domain will be discussed. We propose a method where short measure-ment current pulses of a fixed amplitude are applied to the heater resistor. As an optimization,these pulses are omitted when a certain current threshold has been met.Results show that the system can measure temperature with±1◦C accuracy, however more fullsystem measurements are required to ensure functionality as a whole.

In this work, a MATLAB based graphical user interface (GUI) tool is built to analyze Quasi-optical (QO) systems in reception with the Fourier Optics (FO) and Geometrical Optics (GO) methods. Five canonical QO components are discussed, namely parabolic reflectors, elliptical lenses, hemispherical lenses, hyperbolic lenses, and elliptical mirrors. The ray tracing technique is implemented to describe reception scenarios and visualize the phase aberrations in the QO systems. The FO method represents the fields focalized by a QO component on its focal plane as a Plane Wave Spectrum (PWS). This spectrum is calculated by using the GO method and can be used in spectral techniques like equivalent Floquet circuit. Moreover, the tool is able to use this spectrum to estimate the power delivered to an antenna placed at the focal plane. By obtaining this delivered power, the performance of the antenna-coupled QO system is analyzed, including pattern, directivity, common efficiency terms, and gain. In addition, the performance calculated in reception is validated by CST and GRASP full-wave simulation software. Therefore, this GUI tool represents a GO/FO based tool that can be used to analyze and design antenna-coupled QO systems in reception.

In recent years, Terahertz technology has attracted the interest of researchers for its potential applications in a variety of domains. In particular, THz sensing has found application in security screening, medical imaging, spectroscopy, and non-destructive testing. The emergence of all these applications has been driven by the availability of photoconductive antennas, which have made available bandwidth in the THz spectrum at relatively low cost, thanks to several breakthroughs in photonics, and semiconductor technology. Photoconductive antennas are optoelectronic electromagnetic sources that resort to optically
pumped semiconductor materials. Such devices exploit the photoconductivity phenomenon to generate and radiate power over a broadband up to the THz frequencies. However, nowadays the use of photoconductive antennas are confined to niche short-range applications, because of the bottleneck of the low power emitted. Early in this research work, it was understood that such bottleneck came from the fact that there was not a clear description about the coupling between the photocondcutive source and the antenna. For this reason,
this work has been focused to develop a Thévenin or Norton equivalent circuit for the photoconductor generators of photoconductive antennas.
A Norton equivalent circuit for pulsed photoconductive antennas has been derived, starting by the electrodynamic model of the photogeneration of free carriers in laser pumped semiconductor material. Such equivalent circuit allows to maximize the radiated power as function of the geometry of the gap, the properties of the semiconductor material, and the features of the laser pump, providing a clear description of the coupling between the photoconductor generator and the antenna over the operative bandwidth.
An electromagnetic model of the quasi-optical (source-to-detector) channel, typically used for measuring power and spectrum radiated by photoconductive antennas, has been proposed. Such model jointly with the developed Norton equivalent circuit allows a complete characterization of the power budget from the source to the detector. Providing for the first time a complete description about the dispersion introduced by the quasi-optical channel on the energy spectrum radiated by photoconductive antennas. The entire proposed model (equivalent circuit and channel) has been validated by spectrum and power
measurements of photoconductive antenna prototypes.
The proposed equivalent circuit and the electromagnetic model of the quasi-optical channel provide a powerful engineering tool to design photoconductive antennas, opening the way for more standard engineering optimization of wide band laser pumped sources, resorting to the vast heritage of wide band microwave engineering tools that have been developed mostly for analyzing detectors in radiometric domains.
The radiation performances of logarithmic spiral antennas as feed of dense dielectric lenses has been intensively analyzed. The results of the investigation have demonstrated the presence of the leaky wave radiation, when the spiral antenna are printed at the air dielectric interface, leading to a design of a logarithmic spiral antenna lens antenna, which provides an high aperture efficiency over a decade frequency bandwidth. However, only using extremely thin substrate allows to feed this design with a planar feeding system without limiting the bandwidth. A new design of a logarithmic spiral lens antenna has been proposed for relaxing such limitation, introducing a small air gap between the spiral feed and the bottom lens interface, which enhances the leaky wave radiation. Such new design, coupled with a synthesized elliptical lens, achieves directive patterns without sidelobes over a decade frequency bandwidth. Moreover, the new spiral design can be used also as feed of a hemispherical lens with low extension height, when the dispersion of the radiated pulses has to be minimized.
A novel design for photoconductive sources has been proposed, aiming to increase dramatically the radiated power with respect to the current photoconductive antennas. The new source is based on the well established concept in the microwave community of connected array. Thanks to the intrinsic wide band behavior of the connected array, the proposed solution is able to radiate efficiently the wide band energy spectrum generated by the photoconductive source. Such design is suitable to be employed also as receiver of ultra-wide bandwidth radiation, increasing the sensitivity with respect to the current photoconductive receivers. In order to implement the design of the photoconductive connected array, an ad-hoc biasing network has been proposed, in order to properly bias all the array cells, preserving the connected structure of the elements. Moreover, a design of an optical system has been proposed, in order to optically excite all the elements of the photoconductive array coherently. Using the proposed Norton equivalent circuit for photoconductive generator, a photoconductive connected array generating an average power of 2.35mW over a bandwidth from 0.1THz − 0.4THz has been designed. A demonstrator of the proposed photoconductive source design is going to be realized, and a complete characterization of the prototype will be performed by means of power and spectrum measurements, proving the validity of the concept.@en