Analysis, Design and Measurements of Flat and Curved Circularly Symmetric High Impedance Surfaces for Curvilinear Antenna Applications

abstract: In this dissertation a new wideband circular HIS is proposed. The circular periodicity made it possible to illuminate the surface with a cylindrical TEMz wave and; a novel technique is utilized to make it wideband. Two models are developed to analyze the reflection characteristics of the proposed HIS. The circularly symmetric high impedance surface is used as a ground plane for the design of a low-profile loop and spiral radiating elements. It is shown that a HIS with circular periodicity provides a wider operational bandwidth for curvilinear radiating elements such, such as loops and spirals, compared to canonical rectangular HISs. It is also observed that, with the aid of a circular HIS ground plane the gain of a loop and a spiral increases compared to when a perfect magnetic conductor (PMC) or rectangular HIS is used as a ground plane. The circular HIS was fabricated and the loop and spiral elements were placed individually in close proximity to it. Also, due to the growing demand for low-radar signature (RCS) antennas for advanced airborne vehicles, curved and flexible HIS ground planes, which meet both the aerodynamic and low RCS requirements, have recently become popular candidates within the antenna and microwave technology. This encouraged us, to propose a spherical HIS where a 2-D curvature is introduced to the previously designed flat HIS. The major problem associated with spherical HIS is the impact of the curvature on its reflection properties. After characterization of the flat circular HIS, which is addressed in the first part of this dissertation, a spherical curvature is introduced to the flat circular HIS and its impact on the reflection properties was examined when it was illuminated with the same cylindrical TEMz wave. The same technique, as for the flat HIS ground plane, is utilized to make the spherical HIS wideband. A loop and spiral element were placed in the vicinity of the curved HIS and their performanceswere investigated. The HISs were also fabricated and measurements were conducted to verify the simulations. An excellent agreement was observed.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

ULTRA LOW POWER FSK RECEIVER AND RF ENERGY HARVESTER

This thesis focuses on low power receiver design and energy harvesting techniques as methods for intelligently managing energy usage and energy sources. The goal is to build an inexhaustibly powered communication system that can be widely applied, such as through wireless sensor networks (WSNs). Low power circuit design and smart power management are techniques that are often used to extend the lifetime of such mobile devices. Both methods are utilized here to optimize power usage and sources. RF energy is a promising ambient energy source that is widely available in urban areas and which we investigate in detail. A harvester circuit is modeled and analyzed in detail at low power input. Based on the circuit analysis, a design procedure is given for a narrowband energy harvester. The antenna and harvester co-design methodology improves RF to DC energy conversion efficiency. The strategy of co-design of the antenna and the harvester creates opportunities to optimize the system power conversion efficiency. Previous surveys have found that ambient RF energy is spread broadly over the frequency domain; however, here it is demonstrated that it is theoretically impossible to harvest RF energy over a wide frequency band if the ambient RF energy source(s) are weak, owing to the voltage requirements. It is found that most of the ambient RF energy lies in a series of narrow bands. Two different versions of harvesters have been designed, fabricated, and tested. The simulated and measured results demonstrate a dual-band energy harvester that obtains over 9% efficiency for two different bands (900MHz and 1800MHz) at an input power as low as -19dBm. The DC output voltage of this harvester is over 1V, which can be used to recharge the battery to form an inexhaustibly powered communication system. A new phase locked loop based receiver architecture is developed to avoid the significant conversion losses associated with OOK architectures. This also helps to minimize power consumption. A new low power mixer circuit has also been designed, and a detailed analysis is provided. Based on the mixer, a low power phase locked loop (PLL) based receiver has been designed, fabricated and measured. A power management circuit and a low power transceiver system have also been co-designed to provide a system on chip solution. The low power voltage regulator is designed to handle a variety of battery voltage, environmental temperature, and load conditions. The whole system can work with a battery and an application specific integrated circuit (ASIC) as a sensor node of a WSN network

Two Port Network Theory Based Design Method of Broadband Doherty Power Amplifier

LTE-Advanced (LTE-A) is a widely used communication standard and it mainly features Carrier aggregation (CA). CA increases the user data rate and efficiently exploits the fragmented spectrum by combining various carrier frequencies. The intrinsic multi-band and multi-standard of CA, along with the existing high peak-to-average power ratio (PAPR), brings the challenges of broadband requirement and back-off (BO) efficiency enhancement when designing radio frequency power amplifiers (PA). The above two challenges inspire research interest in designing of broadband Doherty power amplifiers (DPAs), which maintain the high efficiency at BO power level and perform constantly versus frequency. In this work, the continuous design space was discussed. Output combining and matching network (OCMN) and its impact on the impedances shown to the two transistors were analyzed based on two port network theory. ABCD parameters of matching networks was formulated to accommodate continuous class-B (class-J) operation to DPAs. Second harmonic was terminated to avoid clipping and efficiency degradation. By enlarging design space, the bandwidth was substantially expanded. The proposed design methodology allowed the adsorption of parasitics which was the one of the bandwidth limiting factor. To validate the proposed methodology, an 8 Watts DPA was simulated to operate from 3 GHz to 5 GHz using Cree Gallium nitride (GaN) High-electron-mobility transistors (HEMTs). And simulation results showed that the 6dB BO efficiency was above 40% and Peak-envelope-power (PEP) of 50% over the frequency range of 3GHz to 5GHz. The Doherty power amplifier prototype is fabricated on substrate of Rogers4003C and assembled in house. Continuous wave measurement showed that the PA could provide 8.2 - 10.6 dB gain in the frequency band of 2.7 to 4.3 GHz. The 6 dB back off efficiency was 40% to 43%. And at peak power, the drain efficiency reached 48% to 60%. 80 MHz inter-band modulated signal and 15MHz dual band signal measurement were carried out to investigate the linearizability. In the inter-band measurement, average power around 33dBm and average drain efficiency of 46% was obtained with PAPR of 6.4 dB. ACLR above 48.7 dBc after DPD verified the easiness of linearization for this PA. Dual band measurement using two carriers at 2.8 and 3.2 GHz showed even when the PAPR of two band were 7.6 and 8.0 dB separately, average power of 32.3 dBm power can still be extracted with average efficiency of 40.5%. ACLR of 49.5 and 46.7 dBc of those two bands were good endorsement of the capability of inter-band concurrent amplification

Design and implementation of L and X-band filters for the NeXtRAD front end

Microwave filters are required at the RF front end of a research radar called NeXtRAD to suppress out of band transmitted and received signals. NeXtRAD is a multistatic pulse-Doppler radar system, developed at the University of Cape Town (UCT) in collaboration with the University College London (UCL). It has been designed to operate in two frequency bands, designated as L and X-bands. NeXtRAD will be used as a research tool, for the purposes of measuring sea targets and detecting sea clutter. The measured data will be stored in a database, and it will be made freely available to the public for research purposes. A coaxial comb-line filter was designed, manufactured and measured at L-band. The narrow band measurement results showed that the filter was centred at 1300 MHz, with an equal ripple bandwidth of 210 MHz. The filter has a spurious-free window of 2050 MHz at -60 dB, with the first spurious approximately at 2.86 times the operating frequency. The return loss of the filter was 19.52 dB, and the insertion loss at mid-band was 0.14 dB. The measured filter agreed extremely well with the L-band specifications. The X-band iris coupled filter was also designed, manufactured and measured. The narrow band measurement results showed that the filter was centred at 8.5 GHz, with an equal ripple bandwidth of 121 MHz. The spurious-free window of the measured filter at -60 dB was 6.571 GHz, with the first spurious at 1.82 times the operating frequency. The insertion loss of the filter was measured to be 2 dB at mid-band and the return loss of the filter was measured to be 18.58 dB at mid-band. The filters are currently being used at the RF front end of the NeXtRAD system

Recent Advances in Antenna Design for 5G Heterogeneous Networks

The aim of this book is to highlight up to date exploited technologies and approaches in terms of antenna designs and requirements. In this regard, this book targets a broad range of subjects, including the microstrip antenna and the dipole and printed monopole antenna. The varieties of antenna designs, along with several different approaches to improve their overall performance, have given this book a great value, in which makes this book is deemed as a good reference for practicing engineers and under/postgraduate students working in this field. The key technology trends in antenna design as part of the mobile communication evolution have mainly focused on multiband, wideband, and MIMO antennas, and all have been clearly presented, studied and implemented within this book. The forthcoming 5G systems consider a truly mobile multimedia platform that constitutes a converged networking arena that not only includes legacy heterogeneous mobile networks but advanced radio interfaces and the possibility to operate at mm wave frequencies to capitalize on the large swathes of available bandwidth. This provides the impetus for a new breed of antenna design that, in principle, should be multimode in nature, energy efficient, and, above all, able to operate at the mm wave band, placing new design drivers on the antenna design. Thus, this book proposes to investigate advanced 5G antennas for heterogeneous applications that can operate in the range of 5G spectrums and to meet the essential requirements of 5G systems such as low latency, large bandwidth, and high gains and efficiencies

Design, Modelling and Implementation of Several Multi-Standard High Performance Single-Wideband and Multi-Wideband Microwave Planar Filters

The objectives of this work are to review, investigate and model the microwave planar filters of the modern wireless communication system. The recent main stream of microwave filters are classified and discussed separately. Various microwave filters with detailed applications are investigated in terms of their geometrical structures and operational performances. A comprehensive theoretical study of microwave filters is presented. The main types of microwave filters including the basic low-pass filters such as Butterworth and Chebyshev filters are fully analysed and described in detail. The transformation from low-pass prototype filters to high-pass filters, band-pass filters and band-stop filters are illustrated and introduced. Research work on stepped impedance resonator (SIR) and asymmetric stepped impedance resonator (ASIR) structure is presented. The characteristics of λg/4, λg/2 and λg (λg is the guided wavelength of the fundamental frequency in the free space) type SIR resonators, and the characteristic of asymmetric SIR resonator are categorized and investigated. Based on the content mentioned above, novel multi-standard high performance asymmetric stepped impedance resonator single-wideband and dual-wideband filters with wide stopbands are proposed. The methodologies to realize wide passband and wide stop-band filters are detailed. In addition, multi-standard high performance triplewideband, quadruple-wideband and quint-wideband filters are suggested and studied. The measurement results for all prototype filters agree well with the theoretical predictions and simulated results from Ansoft HFSS software. The featured broad bandwidths over single/multiple applicable frequency bands and the high performances of the proposed filters make them very promising for applications in future multistandard wireless communication

Reconfigurable Antennas

In this new book, we present a collection of the advanced developments in reconfigurable antennas and metasurfaces. It begins with a review of reconfigurability technologies, and proceeds to the presentation of a series of reconfigurable antennas, UWB MIMO antennas and reconfigurable arrays. Then, reconfigurable metasurfaces are introduced and the latest advances are presented and discussed

Applications of Antenna Technology in Sensors

During the past few decades, information technologies have been evolving at a tremendous rate, causing profound changes to our world and to our ways of living. Emerging applications have opened u[ new routes and set new trends for antenna sensors. With the advent of the Internet of Things (IoT), the adaptation of antenna technologies for sensor and sensing applications has become more important. Now, the antennas must be reconfigurable, flexible, low profile, and low-cost, for applications from airborne and vehicles, to machine-to-machine, IoT, 5G, etc. This reprint aims to introduce and treat a series of advanced and emerging topics in the field of antenna sensors