Characterisation and Design of Novel Non-Foster Circuits for Electrically Small Antennas

PhDThere is a demand for broadband electrically small antennas that cover large frequency bands without any requirement of reconfiguration techniques. This is particularly true at low frequencies (VHF/UHF), where wavelengths are long and antennas are physically large. The fundamental gain-bandwidth limitation was related to the electrical size of passive electrically small antennas by Wheeler and Chu; their result implied that an electrically small antenna exhibits high quality factor which limits the bandwidth. Additionally, the gain-bandwidth limitation was related to impedance matching conditions by the Bode-Fano criteria, which restricts available bandwidth using conventional reactive elements. A non-Foster circuit approach has been presented which delivers a broadband input impedance match and also overcomes the aforementioned fundamental limits. These non-Foster impedance circuits can be realised by negative impedance converters (negative inductance and/or capacitance). The thesis also explores the advantages and challenges of antenna impedance matching using negative impedance circuits based on two topologies: (1) conventional transistorbased circuits, and (2) a novel resonant tunnelling diode approach. The advantages of non-Foster circuits in the implementation of broadband small antennas include wideband performance around one-tenth of the self-resonant frequency and overcoming of the fundamental limits associated with passive antennas. Diode-based circuits are more compact, easily configurable, less sensitive to stability, have low power consumption and are less complex as compared to the transistor based designs. These features makes it a potential candidate for array and meta-material applications. However, there are few challenges for non-Foster circuit integration with an antenna due to high noise figure, which affects the system channel capacity and receiver performance in a communication system. A detailed design procedure has been developed to mitigate the effects of noise and instability and also, the system performance and measurement of the non-Foster circuit integrated antennas have been discussed

A Novel Method for Tuning a Transistor-Based non-Foster Matching Circuit for Electrically Small Wideband Antennas

This dissertation reviews the application of non-Foster circuits for wideband antenna matching, and introduces a novel, rapid means of “tuning” the circuit to accommodate variations in antenna loadings. The tuning is accomplished via the judicious addition of a common transistor.A detailed literature search is provided, and non-Foster circuits are discussed in detail, including the myriad of implementations with focus on tuning. A comparison between different tuning methods is presented. The novel tuning method is evaluated via the normalized determinant function to ensure stability. Evaluations include simulations using commercially available software and experimentation to ensure not only stability but also that noise added by the active circuitry is manageable. Wideband stable operation is confirmed by pairing the tunable non-Foster matching circuit with an electrically small, resistively loaded dipole, and performance gains are demonstrated using the tunability feature. The resistively loaded dipole alone demonstrates reasonable performance at higher frequencies, but performance degrades considerably at lower frequencies, when the dipole is electrically small. The tunable non-Foster circuit is shown to alleviate some of this degradation. Additionally, applications other than wideband antenna matching can benefit from tunable non-Foster circuits such as tunable filters and phase shifters, and these are discussed as well. Finally, practical limitations of non-Foster circuits are presented

Sensitivity analysis for active matched antennas with non-foster elements

During the last years many researchers have been working on the active matching or on non-Foster matching networks for one- and two-port electrically small antennas (ESAs). A new parameter on the sensitivity of the two-port electrically small antenna when loaded with a non-F oster network is presented. This sensitivity analysis will allow us to choose what kind of antennas can be properly matched with non-Foster networks and their position in order to optimi ze the performance of the design. Then, a typical high Q two-port antenna will be harder to match over a broad bandwidth, since |S21| is very small and only agrees with |S11| over very small frequency bands, yielding very large sensitivity values. However, for these two-port antennas, if high levels of coupling can be engineered for a high Q multiple-port antenna, the return and insertion losses can be similar over larger bandwidths and, hence, the sensitivity can be kept low over larger bandwidths, enabling broader impedance matched bandwidths to be achieved, even for highly resonant antennas

Design method for actively matched antennas with non-foster elements

The design of electrically small antennas (ESAs) loaded with active non-Foster elements is a topic whose interest has grown in the last years. In this communication, a new strategy for the design of actively matched antennas loaded with non-Foster elements is presented. The analysis of different parameters, such as the sensitivity to non-Foster circuit placement, the overall antenna system stability, and current distributions, has to be considered in order to enhance the antenna performance. A design example using an ESA and its realization is presented to validate the proposed strategy.This work was supported in part by MINECO under the project TEC2013-47753-C3-2-R and RTC 2014-2380-4.Publicad

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

Design of Broadband Non-Foster Circuits Based on Resonant Tunneling Diodes

A non-Foster circuit (NFC) based on the resonant tunneling diode (RTD) is proposed for application to broadband impedance matching of electrically small antennas (ESAs). NFCs have traditionally been implemented with transistor pairs to achieve negative impedance, but these have limitations with respect to performance and operational bandwidth at high frequencies. At certain biasing voltages, double barrier RTDs behave as negative differential resistance (NDR) devices, which may be transformed to exhibit negative impedance. In contrast to the transistor-based NFC, these structures serve to gyrate or invert the load impedance, such that an inductive load will lead to a negative capacitance, and vice versa. This device is termed a negative impedance inverter (NII). We demonstrate negative impedance behavior for prototypes with measurements of negative resistance at up to 3 GHz, and device gain of around 5 dB from DC to 4 GHz. Design for stability of the RTD is performed using the Nyquist stability criterion. Stabilized negative capacitance NFCs show optimum performance from DC to the GHz range depending upon the load value. These NFCs are used to impedance match an antenna at low frequencies. An antenna with only one resonance at 3.5 GHz has been transformed with two different matching circuits: to an antenna encompassing the 1 to 2 GHz range; as well as the VHF/UHF bands from 300 MHz to 1 GHz. Additionally, RTDs have been demonstrated for operation at up to THz frequencies, so this topology can be extended to higher frequencies subject to fabrication constraints

Stability and bifurcation analysis of multi-element non-foster networks

A stability and bifurcation analysis of multi-element non-Foster networks is presented, illustrated through its application to non-Foster transmission lines. These are obtained by periodically loading a passive transmission line with negative capacitors, implemented with negative-impedance converters (NICs). The methodology takes advantage of the possibility to perform a stability analysis per subintervals of the perturbation frequency. This will allow an independent analytical study of the low-frequency instability, from which simple mathematical criteria will be derived to prevent bias-network instabilities at the design stage. Then, a general numerical method, based on a combination of the Nyquist criterion with a pole-zero identification of the individual NIC, will be presented, which will enable the detection of both low- and high-frequency instabilities. A bifurcation analysis of the multi-element non-Foster structure will also be carried out, deriving the bifurcation condition from a matrix-form formulation of the multi-element structure. The judicious choice of the observation ports will enable a direct calculation of all the coexisting bifurcation loci, with no need for continuation procedures. These bifurcation loci will provide useful insight into the global-stability properties of the whole NIC-loaded structure.This work was supported in part by the Spanish Ministry of Economy and Competitiveness and in part by the European Regional Development Fund (ERDF/FEDER) under Project TEC2014-60283-C3-1-R and Project TEC2017-88242-C3-1-R

Bandwidth and gain enhancement of composite right left handed metamaterial transmission line planar antenna employing a non foster impedance matching circuit board

The paper demonstrates an effective technique to significantly enhance the bandwidth and radiation gain of an otherwise narrowband composite right/left-handed transmission-line (CRLH-TL) antenna using a non-Foster impedance matching circuit (NF-IMC) without affecting the antenna's stability. This is achieved by using the negative reactance of the NF-IMC to counteract the input capacitance of the antenna. Series capacitance of the CRLH-TL unit-cell is created by etching a dielectric spiral slot inside a rectangular microstrip patch that is grounded through a spiraled microstrip inductance. The overall size of the antenna, including the NF-IMC at its lowest operating frequency is 0.335 lambda (0)x0.137 lambda (0)x0.003 lambda (0), where lambda (0) is the free-space wavelength at 1.4 GHz. The performance of the antenna was verified through actual measurements. The stable bandwidth of the antenna for |S-11|<= -18 dB is greater than 1 GHz (1.4-2.45 GHz), which is significantly wider than the CRLH-TL antenna without the proposed impedance matching circuit. In addition, with the proposed technique the measured radiation gain and efficiency of the antenna are increased on average by 3.2 dBi and 31.5% over the operating frequency band

Electrically small metamaterial-inspired antennas with active near field resonant parasitic elements: From theory to practice

© 2017 Euraap. By augmenting several classes of metamaterial-inspired near-field resonant parasitic (NFRP) electrically small antennas (ESAs) with active (non-Foster) circuits, we have achieved performance characteristics surpassing their fundamental passive bounds. The designs not only have high radiation efficiencies, but they also exhibit large frequency bandwidths, large beam widths, large front-to-back ratios, and high directivities. Furthermore, the various initially theoretical and simulated designs have led to practical realizations. These active NFRP ESAs will be reviewed and recently reported designs will be introduced and discussed