In this thesis, a design of a passive radar for use on a drone used in inhospitable areas where air traffic control is not available due to circumstances. The thesis focusses on the receiver chain and angle of arrival algorithm.

A system has been developed that utilises the techniques of Ultra Wideband and Synthetic Aperture Radar to produce top view images of a scene using measurements from the side. The system consists of the PulsON P410 radar module, a set of antennas, a moving platform and an imaging algorithm. This thesis will cover all the aspects of the data acquisition part of the system with additionally an analysis on antennas.

This thesis presents the development of circuits and systems for fast wireline transceiver links that will enable a move towards highly integrable RF digital-to-analog converters. A new perspective on the analysis of bit error rates in wireline links leads to the PAM spectral design space chart: a novel, visual system design analysis tool for PAM wireline circuit designers. Moreover, a <2 mW/Gbps/lane, 10 Gbps wireline transmitter has been designed and taped-out in 40 nm CMOS. The proposed inherently pipelined 16:1 multiplexer and current mode logic driver design procedure are the key enablers for this performance. Finally, for development of a 10 Gbps wireline receiver, a novel self-synchronized receiver design is proposed that removes the need of a classical clock and data recovery loop. At its core, this receiver comprises the design of a high-speed two-tail comparator and an asynchronous metastability detection loop.

Vagus nerve stimulation (VNS) has been proven to be an effective treatment for patients suffering from drug­-resistant epilepsy. Current vagus nerve stimulators are either implantable devices or bulky, handheld devices. The implant consists of a pulse generator beneath the skin of the chest, connected to electrodes that are wired to the cervical vagus nerve. While capable of delivering localized electrical impulses, the implantation is highly invasive. Handheld devices do not ask for a risky surgery, but their imprecise targeting of the neck reduces efficiency and provokes additional side effects. Ultrasound has been widely used in clinical applications ranging from focused ultrasound (FUS) tissue ablation to medical imaging. Much research is being carried out on the use of FUS neuromodulation as a low-­cost, non-invasive alternative to electrical VNS. The combination of using ultrasound for neuromodulation as well as imaging allows for image-­guided FUS where automated tracking of the nerve location improves the targeting of the vagus nerve. In this thesis, the design of an ultrasound vagus nerve stimulator with combined imaging capabilities is presented. The novel architecture combines FUS for vagus nerve neuromodulation and plane wave imaging (PWI) with optimized sparse receive sub­arrays to obtain the location of the nerve within the neck. A 2D array of piezoelectric transducers with λ/2-pitch poses a strict constraint on the pixel area. The goal of the system design is to minimize the area consumption of the on­-pixel electronics by making use of already present circuit blocks. A shared delay­-locked loop generates the required continuous phases for FUS neuromodation, while a row-­column pulse control block generates a single pulse from the available phases for use in PWI. This way the on-­pixel transmit hardware is reduced to a multiplexer and high­-voltage driver. The receiver consists of an analog front­-end and analog-­to­-digital converter and is shared among a sub-­array of receive elements. Different degrees of random sparsity are explored for the optimal implementation of the receive sub-­arrays within the full array. Synthetic aperture imaging allows the multiplexing of multiple receive elements to the shared front-­end and reduces the time spent on imaging using dynamic beamforming on a single data set. The full system­-level architecture of a complementary metal­-oxide­-semiconductor (CMOS) interface is proposed and the receiver front-end has been designed and simulated.

The most common serious heart rhythm disease is atrial fibrillation. It is not fatal on its own but does increase the risk of heart failures and strokes. There is little understanding about the mechanisms behind the disease, so more insight is desired. Using an array of electrodes, measurements are being performed of the electrical atrial activity directly on the heart tissue. These signals are, however, not clean and suffer from far-field interference coming from the ventricles. During normal sinus rhythm these atrial and ventricular activities are separated in time and easy to distinguish. In case of atrial fibrillation this is not always the case. Luckily, there is a major difference between both signals: the ventricular signal comes from far away and arrives therefore approximately simultaneously at all electrodes. A simple, but effective way to remove this ventricular activity is to use a bipolar electrode. It produces the difference between two normal unipolar electrodes, thus removing the common ventricular signal component. The bipolar electrode, however, distorts the atrial signal component, which in some orientations can even lead to removing it altogether. This bipolar electrode is known as a differential beamformer from the field of array signal processing. There are more complex beamformers that can keep the atrial component undistorted and therefore produce better results than the bipolar electrode. This thesis proposes a Fourier-domain signal model for all available electrodes relying on an atrial and ventricular transfer function. It is possible to estimate these transfer functions from the data blindly. Three beamformers are derived utilizing the signal model and the transfer functions. The bipolar electrode is extended to multiple electrodes like the other beamformers as well. Experiments with simulated data show that the complex beamformers indeed keep the atrial activity undistorted and are still able to remove the ventricular activity effectively when using multiple electrodes, except for very complex data where the signal model is not valid. For low numbers of electrodes the beamformers are not useful, they hardly remove the ventricular activity while keeping the atrial component undistorted, where the bipolar electrode does the opposite. The electrograms are also used to estimate local activation times of the cells underneath the electrodes which says something about the health of the cardiac tissue. Besides the mentioned filtering, this thesis proposes a method to estimate those moments in time by looking at the time-domain version of the atrial transfer function, called the atrial impulse response. For simple data, it performs well compared to state-of-the-art methods, but for more complicated data, it does not.

Flat lens antennas are convenient solutions to realize highly directive antennas for millimeter wave and terahertz frequencies. Unlike the traditional three-dimensional bulky lens antennas, flat lenses are compact, low profile, and planar structures that can be manufactured with standard multi-layer technology, e.g. printed circuit board (PCB) or low temperature cofired ceramic (LTCC). A common tradeoff in the design of flat lenses is between bandwidth and thickness. Electrically thin lenses are characterized by narrow frequency bandwidth, resulting from the phase wrapping adopted in the design. On the other hand, a wide bandwidth can be achieved by avoiding phase wrapping and using true-time-delay phase delay, but this is achieved at the cost of increased electrical thickness. In this thesis, artificial dielectric layers (ADLs), consisting of periodic metal patches within a dielectric substrate, are proposed to realize flat lenses with large effective refractive index, which is a key property for reducing the thickness of wideband true-time-delay flat lenses. As such, ADLs are promising solution to achieve a good compromise between bandwidth and thickness. Different aspects of ADL flat lenses are investigated in this thesis, going from the analysis to the design and experimental validation. For the analysis, a general procedure to find the permittivity profile of a gradient index (GRIN) lens is introduced. The method allows to design GRIN lenses that manipulate the phase front in different ways, by using a Geometrical Optics (GO) approach. Different cases are studied, including collimating lenses with on-axis and off-axis feeds; lenses that transform spherical wavefronts across different media; lenses changing the focal number of a quasi-optical system and Fresnel zone lenses. The design equations are validated by ray-tracing simulations in non-homogeneous media, implemented by numerical solution of the Eikonal equation. Once the permittivity profile is defined, the continuous variation of refractive index is discretized into unit cells. Each unit cell is then implemented as an ADL stack, using ADL synthesis models developed earlier in the THz sensing group. To validate the design procedure, an ADL flat lens with an operation band from 30 to 60 GHz is designed and fabricated using an eight-layer print circuit board (PCB) stackup. The measurement results reach good agreements with the simulation results and validate the design. The achieved performance demonstrate wideband operation, with a high taper efficiency (> 90%) and a maximum directivity of 25.5 dB. The lens is thinner than 1 wavelength within the band of operation. The lens performance is demonstrated with a simple open-end waveguide as feed, which has high spillover losses. Diverse feeding antennas that can achieve higher aperture efficiency are also analysed by means of simulations. Additionally, other types of GRIN lens, that manipulates the wavefront in distinct ways for different applications are investigate, to highlight the flexibility of the concept.

Nowadays, localization of cars is mostly done using GPS. Some major disadvantages of this method are that it is not very accurate and that it cannot be used indoors. These disadvantages do not form a major problem when an active human driver is controlling the car, but will become more critical when the autonomy of vehicles increases. The goal of this project is to use Synthetic Aperture Radar techniques to overcome the problems of GPS. To achieve this, different imaging algorithms have been implemented, and a single method has been extended to directly accommodate the road-mapping application. Different measurements were done to test the algorithms and the results were promising. It is hoped that the use of this technology will become wide-spread and that it can help with creating a safer and more efficient world of traffic, where increased self-driving capabilities are facilitated.

In the context of the Bachelor Graduation Project at the Delft University of Technology Department of Electrical Engineering, we have been tasked with a project to design prototype of a bi-static radar. This thesis describes the waveform design of a bi-static radar system and its implementation with Software Design Radio, SDR for short. The radar system can be mounted on delivery drones and used to detect other drones and obstacles to avoid collisions. The thesis focuses mainly on the radar waveform design. In addition, the thesis provides analysis of the radar system performance and system implementation with commercial off the shelf SDR. A proof of concept has been realised by means of simulations using the open source software GNU Radio Companion.

This thesis details the design and development of the Power System for the Rover Deployment System. This power system delivers and manages the necessary power required by the entire Rover Deployment System. The RDS is responsible for ensuring the rover’s survival inside the transportation pod during transit. It also handles releasing the rover, which a mechanical mechanism will lower onto the lunar surface. The goal of Lunar Zebro is to send a nanosatellite to the moon for lunar surface exploration and radiation measurements. The power system was designed to power the MCU and transceivers at 3.3V, to provide power for rover charging at 12V, and to charge a capacitor bank used to provide the necessary actuation power to the NEAs. An electrically triggered umbilical release mechanism, unfortunately, could not be implemented due to a lack of available data. The circuit for this system was created, simulated, and added to the PCB design of the RDS. The simulations of the circuit behaved desirably. Due to the lead time on orders, the PCB has unfortunately not been received yet. Because of this, the entire power system has unfortunately not been tested yet.

The analysis of integrated front ends operated in the high-frequency regimes is addressed in this work. The analysis of these problems has been a critical bottleneck for decades due to the difficulties arising in adopting full-wave techniques. Assuming, as typical at lower frequencies, that the structures are planar leads to the inaccurate representation of some characteristic reactive behaviors. As a case in point, the characteristic impedance of transmission lines, whose thickness is comparable to the width, is not well represented by planar tools. Moreover, existing analytic formulas based on quasi-static approximations for the surrounding fields typically fail when the dynamic components of the fields are also affected by the stratifications. In this thesis, planar stratified media with transmission lines and radiators are considered to be part of the front end, with this latter being integrated (or in package) thanks to the systematic presence of a dielectric lens antenna.

Estimating the transmembrane currents travelling through the epicardium and local activation times based on atrial epicardial electrograms can greatly help in the study of cardiac arrhythmias such as atrial fibrillation. This work focuses on the accurate estimation of the aforementioned signals and features. To do this, two least squares-based regression methods were used to estimate transmembrane currents from electrograms and then find their local activation times by searching for the maximum negative slope. The first least squares optimization method consists of using standard least squares, while the second consists of regularized least squares, by combining both lasso and ridge regression, to deal with signal sparsity and multicollinearity, respectively. Furthermore, to improve estimation results, multiresolution analyses based on wavelet decompositions and principal components analysis were used to filter out parasitic components that were present in the estimated transmembrane currents by separating them from the main activation complex of the decomposed signals. Using these algorithms on simulated data, it was shown that promising results can be achieved for both transmembrane current estimations and LAT estimations. Several wavelet support sizes were tested on the simulated data to observe performance changes. These were compared to an already existing LAT estimation algorithm. The results mainly confirm the efficiency of the proposed methods on severely diseased tissue corrupted by conduction blocks and noise.

Phased arrays have emerged as a key solution for 5G base stations, to provide higher capacity by means of directive and electronically steerable beams. However, the implementation of workable low-cost antenna arrays for base stations is very challenging, because of the requirements on the total frequency and angular coverage of 5G systems. When many frequency bands are used for different services, having a single narrowband antenna for each sub-band becomes unfeasible for cost and space occupation. For this reason wideband arrays that can cover simultaneously multiple bands are gaining interest. Moreover, a large field of view is required, i.e. scanning at least from -60° to +60°, so that only a few array panels can cover the entire azimuthal angle of 360°. This thesis work has been performed in the framework of a collaboration between Terahertz Sensing Group and HUAWEI, aiming at the development of a wideband phased array for base station. Two array designs are targeted, one covering 6-8 GHz and another for 2-8 GHz. Both designs are required to achieve wide scanning capability up to 60° in all azimuth planes. This thesis focuses on the design of the feeding structure of the array unit cell and the corporate feeding networks. The unit cell feeding structure is based on integrated coaxial lines connected to microstrips or striplines. The performance is analysed first for the stand-alone transition and then for the same feed together with the connected slot element. The entire unit cell including the feed has comparable matching performance with the ideal one without feeding structure. An alternative feed design is also presented, where the input is realized with a coaxial SMP connector. The design of a corporate feeding network for the array is introduced. This consists of two designs of 1-to-32 power dividers, one implemented with microstrip transmission lines and the other with striplines. Such dividers are meant to feed in phase an entire row or column of the array. The highlights of this design is wide bandwidth, which covers two octaves by means of wideband multi-section and tapered impedance transformers, and the compactness, since the entire divider has to fit in an area of 480 mm × 15 mm. Moreover a novel feeding strategy is proposed to simplify the complexity and the costs of the unit cell. The new approach is based on replacing the coaxial lines with integrated parallel plate waveguides (PPW). Two examples of unit cell design are presented: one consists in a single-polarized array of connected slot, covering the band from 70 GHz to 140 GHz, for automotive radars; another example is referring to a dual-polarized connected slot array covering the same 2-8 GHz range, for wideband base stations. The design procedure of a PPW and cavity is easier than that of the integrated coaxial, as the feed and the radiating slot design are better decoupled. The number of layers of the ADL is also reduced with respect to the integrate coaxial, because part of the impedance transformation is implemented in the PPW.

Typical antenna arrays are designed such that the active element pattern is symmetric around the broadside direction. However, applications exist, for example in satellite communication, where a symmetric pattern is not needed or even unwanted. This angular selectivity can be achieved using asymmetric elements. However, it is known that for well sampled infinite arrays the asymmetry of the active element pattern disappears. Although designs of under-sampled antenna arrays achieving an asymmetric active element pattern have been presented in literature, the fundamental properties of this type of arrays in terms of radiation characteristics have not been investigated in detail. This thesis studies the asymmetry in the active element pattern of a finite linear array of asymmetric elements. To this end an in-house method of moments code is developed in Matlab to simulate tilted dipoles in free space and in the proximity of a ground plane. The dependency of the asymmetry of the active element pattern on the inter-element distance, the skew angle of the elements and the number of elements in the array is analyzed and design rules are derived. Using entire domain basis functions, closed form expressions for spectral integrals and the periodicity of the array the implemented code enables the simulation of large arrays in a much shorter time compared to commercially available software, such as CST. Regarding the choice of antenna element, a dipole bent into a Z-shape is proposed as an alternative for a tilted dipole. This type of dipole can be defined to have an equivalent radiation pattern to that of a tilted dipole. This shape of dipole can be implemented using standard PCB technology using horizontal metal strips and vertical vias. The Z-shaped dipoles are analyzed using a method of moments code based on horizontal and vertical dipoles. The spectral Green's function of stratified media can be included in the spectral domain expressions to account for the presence of dielectric slabs in realistic designs.

In this work, the analytical models to describe artificial dielectric layers (ADLs), when a lateral shift between layers is present, is presented. The alternate lateral displacement between layers is an important parameter to engineer the desired effective electromagnetic properties of the equivalent homogeneous material realized with the ADLs. More specifically, the equivalent dielectric constants that can be realized by alternatively shifting the layers are higher compared to the aligned case. Closed-form expressions are derived for the equivalent layer reactance that includes the higher-order interaction between shifted layers. Furthermore, the effect of finite conductivity of the metal patches is studied and included to the extended versions of the formulas. The given analytical formulas can be used to derive an equivalent circuit model that describes the scattering parameters of a plane wave impinging on a slab composed by an arbitrary finite number of metal layers. To aid the design of artificial dielectric slabs, the effective permittivity and permeability tensors are also retrieved from the scattering parameters.

In the context of designing a real-time brain-computer interface for playing a game using the OpenBCI Ultracortex "Mark IV" headset, this paper focuses on the work of the decoding subgroup. The primary responsibility is to analyse EEG data retrieved from the OpenBCI headset and classify the intention of the user. Our objective is to achieve a high-accuracy classification of the EEG signals. The paper is structured into three main sections: preprocessing, feature extraction, and classification. Multiple methods for preprocessing and classification of motor execution EEG signals will be analysed, striving to contribute to the real-time implementation of the project. The results of our work provides valuable insights for future research and development in this field.