Design strategies for electrically small antennas, actively matched with non-foster elements

Mención Internacional en el título de doctorDuring the last years, some researchers have been working on active matching or on non-Foster matching networks for electrically small antennas (ESAs), in response to the vertiginous increase in demand for compact devices working in multiband platforms. The inclusion of non- Foster networks allows broad bandwidths at lower frequencies, overcoming the inherent limitations derived from the high-quality factor (Q) property of ESAs. Thus, the development of multiband antennas with an engineered lower broadband obtained by embedding an active non- Foster matching network (MN) is one of the primary objectives addressed in this work. Such non-Foster MNs are implemented by using Negative Impedance Converters (NICs), introduced many years ago to realize negative capacitors or negative inductors that disobey the Foster's reactance theorem. In this sense, an integral design methodology of actively matched ESAs with embedded non-Foster elements is proposed and developed. This design method takes into account the operating parameters inherent to a radiating element, such as efficiency and radiation pattern, impedance matching, realizability, and stability. A new parameter (called Sens) on the sensitivity of the ESA when loaded with a non-Foster form is introduced. This sensitivity analysis will allow us to choose not only the kind of antennas that can be properly matched with non-Foster networks but also the most suitable position of such networks into the antenna structure, in order to optimize the performance of the design. The design methodology can be easily extended to any type of antenna, disregarding its electrical size. Two electrically small antennas are presented as design examples in which the proposed design strategy is applied. First, a printed small semiloop antenna, which is resonant at 1200 MHz, is loaded with an embedded MOSFET-based NIC, resulting in a new lower-band with a fractional bandwidth (FBW) of 119% (centered at 117 MHz). Second, a blade-type monopole, whose resonant frequency is around 300 MHz, is loaded with an embedded non-Foster MN, resulting in a new working band whose FBW of 82% (centered at 85 MHz). The notable results in terms of impedance bandwidth and miniaturization level encouraged us to keep seeking for solutions for radiation pattern changes and added noise issues. Finally, the proposed design strategy is applied to fewelement antenna arrays to obtain a multiband performance, keeping unchanged the natural response of the host structure (i.e. around its resonant frequency).Durante los últimos años, algunos investigadores han venido trabajando en la inclusión de redes de adaptación tipo non-Foster en antenas eléctricamente pequeñas (Electrically Small Antennas, ESA). Esto en respuesta a la creciente demanda de dispositivos compactos, que funcionen a diferentes bandas de frecuencia, como parte de los modernos sistemas y plataformas multibanda. La consecución de sistemas compactos y de banda ancha, así como la obtención de múltiples frecuencias de trabajo han sido uno de los objetivos primarios de la presente tesis doctoral. La inclusión de estructuras non-Foster, que reciben este nombre debido a que no obedecen a las propiedades establecidas por el teorema de R. M. Foster en 1924, permite el ensanchamiento de la banda de adaptación de impedancia o la obtención de una banda adicional para una misma estructura radiante. Dentro de los circuitos más representativos de las redes non-Foster se encuentran los Convertidores de Impedancia Negativa (Negative Impedance Converter, NIC), comúnmente implementados con transistores, a través de los cuales es posible la implementación de inductores o de condensadores “negativos”. La realización de una impedancia “negativa” por medio de un NIC, es de vital importancia en la adaptación de la impedancia de antena en banda ancha que se busca en este trabajo. En este sentido, se hace necesario establecer una metodología de diseño de este tipo de antenas, que tenga en cuenta los parámetros de funcionamiento inherentes a un elemento radiante, como son: eficiencia y diagrama de radiación, adaptación de impedancias, factibilidad y estabilidad. Esto, a través del análisis de la sensibilidad a la ubicación de puertos (propuesto en este proyecto), análisis de estabilidad del sistema completo (antena y red de adaptación activa), análisis de distribución de corrientes etc., hace que la estrategia de diseño que se pretende desarrollar y describir pueda resultar una herramienta realmente útil en el diseño de las mencionadas antenas. El parámetro de sensibilidad, Sens, introducido en este trabajo, otorga al diseñador un criterio de selección cuantitativo con respecto a qué tipo de antena puede, en efecto, ser adaptada con elementos non-Foster y la posición misma de _estos dentro de la estructura. De este modo, el parámetro Sens constituye una herramienta de optimización del desempeño del sistema radiante diseñado. Adicionalmente, cabe mencionar que la metodología de diseño propuesta y desarrollada en esta tesis puede ser aplicada a cualquier tipo de antena, sin importar su naturaleza ni su tamaño en términos eléctricos. Luego de desarrollada y descrita la metodología |estrategia| de diseño, se presentan dos antenas eléctricamente pequeñas a manera de ejemplos de diseño. La primera consiste en un semilazo impreso sobre un dieléctrico, resonante a 1200 MHz, cargado con un NIC compuesto de transistores MOSFET. Como resultado, se obtiene una nueva banda de trabajo cuyo ancho de banda de adaptación relativo (FBW) es de 119% (centrado en 117 MHz). La segunda antena ejemplo consiste en un monopolo ensanchado, tipo aleta (blade-monopole), en cuya estructura es embebida una red de adaptación activa, basada también en transistores MOSFET. En este segundo caso, se obtuvo una banda adicional con un FBW de 82% (centrado en 85 MHz). Los notables resultados en términos de adaptación de impedancia y de nivel de miniaturización de las estructuras radiantes, alentaron al autor a continuar con la búsqueda de alternativas de solución a los cambios en el diagrama de radiación observados y a el nivel de ruido adicionado por la red activa embebida. Finalmente, la estrategia de diseño descrita es aplicada a arreglos (arrays) de antenas de pocos elementos, en busca de obtener un comportamiento multibanda en el que la banda incluida comprenda frecuencias a las que toda la estructura es eléctricamente pequeña.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Milos Mazánek.- Secretario: Luis Enrique García Muñoz.- Vocal: Marco A. Antoniade

Microwave Antennas for Energy Harvesting Applications

In the last few years, the demand for power has increased; therefore, the need for alternate energy sources has become essential. Sources of fossil fuels are finite, are costly, and causes environmental hazard. Sustainable, environmentally benign energy can be derived from nuclear fission or captured from ambient sources. Large-scale ambient energy is widely available and large-scale technologies are being developed to efficiently capture it. At the other end of the scale, there are small amounts of wasted energy that could be useful if captured. There are various types of external energy sources such as solar, thermal, wind, and RF energy. Energy has been harvested for different purposes in the last few recent years. Energy harvesting from inexhaustible sources with no adverse environmental effect can provide unlimited energy for harvesting in a way of powering an embedded system from the environment. It could be RF energy harvesting by using antennas that can be held on the car glass or building, or in any places. The abundant RF energy is harvested from surrounding sources. This chapter focuses on RF energy harvesting in which the abundant RF energy from surrounding sources, such as nearby mobile phones, wireless LANs (WLANs), Wi-Fi, FM/AM radio signals, and broadcast television signals or DTV, is captured by a receiving antenna and rectified into a usable DC voltage. A practical approach for RF energy harvesting design and management of the harvested and available energy for wireless sensor networks is to improve the energy efficiency and large accepted antenna gain. The emerging self-powered systems challenge and dictate the direction of research in energy harvesting (EH). There are a lot of applications of energy harvesting such as wireless weather stations, car tire pressure monitors, implantable medical devices, traffic alert signs, and mars rover. A lot of researches are done to create several designs of rectenna (antenna and rectifier) that meet various objectives for use in RF energy harvesting, whatever opaque or transparent. However, most of the designed antennas are opaque and prevent the sunlight to pass through, so it is hard to put it on the car glass or window. Thus, there should be a design for transparent antenna that allows the sunlight to pass through. Among various antennas, microstrip patch antennas are widely used because they are low profile, are lightweight, and have planar structure. Microstrip patch-structured rectennas are evaluated and compared with an emphasis on the various methods adopted to obtain a rectenna with harmonic rejection functionality, frequency, and polarization selectivity. Multiple frequency bands are tapped for energy harvesting, and this aspect of the implementation is one of the main focus points. The bands targeted for harvesting in this chapter will be those that are the most readily available to the general population. These include Wi-Fi hotspots, as well as cellular (900/850 MHz band), personal communications services (1800/1900 MHz band), and sources of 2.4 GHz and WiMAX (2.3/3.5 GHz) network transmitters. On the other hand, at high frequency, advances in nanotechnology have led to the development of semiconductor-based solar cells, nanoscale antennas for power harvesting applications, and integration of antennas into solar cells to design low-cost light-weight systems. The role of nanoantenna system is transforming thermal energy provided by the sun to electricity. Nanoantennas target the mid-infrared wavelengths where conventional photo voltaic cells are inefficient. However, the concept of using optical rectenna for harvesting solar energy was first introduced four decades ago. Recently, it has invited a surge of interest, with different laboratories around the world working on various aspects of the technology. The result is a technology that can be efficient and inexpensive, requiring only low-cost materials. Unlike conventional solar cells that harvest energy in visible light frequency range. Since the UV frequency range is much greater than visible light, we consider the quantum mechanical behavior of a driven particle in nanoscale antennas for power harvesting applications

Radio frequency energy harvesting for autonomous systems

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyRadio Frequency Energy Harvesting (RFEH) is a technology which enables wireless power delivery to multiple devices from a single energy source. The main components of this technology are the antenna and the rectifying circuitry that converts the RF signal into DC power. The devices which are using Radio Frequency (RF) power may be integrated into Wireless Sensor Networks (WSN), Radio Frequency Identification (RFID), biomedical implants, Internet of Things (IoT), Unmanned Aerial Vehicles (UAVs), smart meters, telemetry systems and may even be used to charge mobile phones. Aside from autonomous systems such as WSNs and RFID, the multi-billion portable electronics market – from GSM phones to MP3 players – would be an attractive application for RF energy harvesting if the power requirements are met. To investigate the potential for ambient RFEH, several RF site surveys were conducted around London. Using the results from these surveys, various harvesters were designed and tested for different frequency bands from the RF sources with the highest power density within the Medium Wave (MW), ultra- and super-high (UHF and SHF) frequency spectrum. Prototypes were fabricated and tested for each of the bands and proved that a large urban area around Brookmans park radio centre is suitable location for harvesting ambient RF energy. Although the RFEH offers very good efficiency performance, if a single antenna is considered, the maximum power delivered is generally not enough to power all the elements of an autonomous system. In this thesis we present techniques for optimising the power efficiency of the RFEH device under demanding conditions such as ultra-low power densities, arbitrary polarisation and diverse load impedances. Subsequently, an energy harvesting ferrite rod rectenna is designed to power up a wireless sensor and its transmitter, generating dedicated Medium Wave (MW) signals in an indoor environment. Harvested power management, application scenarios and practical results are also presented

Design of antenna array and data streaming platform for low-cost smart antenna systems

The wide range of wireless infrastructures such as cellular base stations, wireless hotspots, roadside infrastructures, and wireless mobile infrastructures have been increasing rapidly over the past decades. In the transportation sector, wireless technology refreshes require constantly introducing newer wireless standards into the existing wireless infrastructure. Different wireless standards are expected to co-exist, and the air space congestion worsens if the wireless devices are operating in different wireless standards, where collision avoidance and transmission time synchronisation become complex and almost impossible. Huge challenges are expected such as operation constraints, cross-system interference, and air space congestion. Future proof and scalable smart wireless infrastructures are crucial to harmonise the un-coordinated wireless infrastructures and improve the performance, reliability, and availably of the wireless networks. This thesis presents the detailed design of a novel pre-configurable smart antenna system and its sub-system including antenna element, antenna array, and radio frequency (RF) frontend. Three types of 90° beamforming antenna array (with low, middle and high gain) were designed, simulated, and experimentally evaluated. The RF frontend module or transmit and receive (T/R) module was designed and fabricated. The performance of the T/R module was characterised and calibrated using the recursive calibration method, and drastic sidelobe level (SLL) improvement was achieved using the amplitude distribution technique. Finally, the antenna arrays and T/R modules are integrated into the pre-configurable smart antenna system, the beam steering performance is experimentally evaluated and presented in this thesis. With the combination of practical know-how and theoretical estimation, the thesis highlights how the modern smart antenna techniques that support most cutting-edge wireless technology can be adopted into the existing infrastructure with minimum distraction to the existing systems. This is in line with the global Smart City initiative, where a huge number of Internet of Things (IoT) devices being wired, or wireless are expected to work harmoniously in the same premises. The concept of the pre-configurable smart antenna system presented in this thesis is set to deliver a future-proof and highly scalable and sustainable infrastructure in the transportation market

Antenna and rectifier designs for miniaturized radio frequency energy scavenging systems

With ample radio transmitters scattered throughout urban landscape, RF energy scavenging emerges as a promising approach to extract energy from propagating radio waves in the ambient environment to continuously charge low power electronics. With the ability of generating power from RF energy, the need for batteries could be eliminated. The effective distance of a RF energy scavenging system is highly dependent on its conversion efficiency. This results in significant limitations on the mobility and space requirement of conventional RF energy scavenging systems as they operate only in presence of physically large antennas and conversion circuits to achieve acceptable efficiency. This thesis presents a number of novel design strategies in the antenna and rectifier designs for miniaturized RF energy scavenging system. In the first stage, different energy scavenging systems including solar energy scavenging system, thermoelectric energy scavenging system, wind energy scavenging system, kinetic energy scavenging system, radio frequency energy scavenging system and hybrid energy scavenging system are investigated with regard to their principle and performance. Compared with the other systems, RF energy scavenging system has its advantages on system size and power density with relatively stable energy source. For a typical RF energy scavenging system, antenna and rectifier (AC-DC convertor) are the two essential components to extract RF energy and convert to usable electricity. As the antenna occupies most of the area in the RF energy scavenging system, reduction in antenna size is necessary in order to design a miniaturized system. Several antennas with different characteristics are proposed in the second stage. Firstly, ultra-wideband microstrip antennas printed on a thin substrate with a thickness of 0.2 mm are designed for both half-wave and full-wave wideband RF energy scavenging. Ambient RF power is distributed over a wide range of frequency bands. A wideband RF energy scavenging system can extract power from different frequencies to maximize the input power, hence, generating sufficient output power for charging devices. Wideband operation with 4 GHz bandwidth is obtained by the proposed microstrip antenna. Secondly, multi-band planar inverted-F antennas with low profile are proposed for frequency bands of GSM 900, DCS 1800 and Wi-Fi 2.4 GHz, which are the three most promising frequency bands for RF energy scavenging. Compared with previous designs, the triple band antenna has smaller dimensions with higher antenna gain. Thirdly, a novel miniature inverted-F antenna without empty space covering Wi-Fi 2.4 GHz frequency band is presented dedicated for indoor RF energy scavenging. The antenna has dimensions of only 10 × 5 × 3.5 mm3 with appreciable efficiency across the operating frequency range. In the final stage, a passive CMOS charge pump rectifier in 0.35 μm CMOS technology is proposed for AC to DC conversion. Bootstrapping capacitors are employed to reduce the effective threshold voltage drop of the selected MOS transistors. Transistor sizes are optimized to be 200/0.5 μm. The proposed rectifier achieves improvements in both power conversion efficiency and voltage conversion efficiency compared with conventional designs. The design strategies proposed in this thesis contribute towards the realization of miniaturized RF energy scavenging systems

Satellite Communications

This study is motivated by the need to give the reader a broad view of the developments, key concepts, and technologies related to information society evolution, with a focus on the wireless communications and geoinformation technologies and their role in the environment. Giving perspective, it aims at assisting people active in the industry, the public sector, and Earth science fields as well, by providing a base for their continued work and thinking

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium