UWB antennas for wireless communications

This thesis focuses on four inter-related research topics on the design and analysis of compact planar ultra wide-band (UWB) monopole antennas for future wireless communications, namely, a planar super-wide-band (SWB) monopole antenna, a planar UWB antenna with band-notched characteristics, a planar UWB antenna with reconfigurable band-rejection features, and a planar UWB multiple-input and multiple-output (MIMO) antenna. A novel Mickey-mouse shaped planar monopole antenna with SWB performance is proposed and investigated. Three different techniques for bandwidth enhancement are implemented. The antenna is evolved from the traditional circular monopole antenna and has achieved an impedance bandwidth of more than 100:1 and a stable radiation patterns over a wider bandwidth. The design of a compact planar UWB monopole antenna (22 mm × 34 mm), incorporated with five m-shaped resonators (MSRs) at different positions, to achieve quintuple-band-notched performance is presented. The frequency-domain performance (in term of reflection coefficients, realized gain, efficiency, and radiation pattern), and time-domain performance (in term of pulse responses and fidelity), are investigated by simulation and measurement. The results show that the proposed UWB antenna has approximately omnidirectional radiation patterns and excellent band-notched behaviours and good time domain performance with the fidelity of more than 85.5% in the pulse response. A planar UWB monopole antenna with reconfigurable band-notched characteristics is also introduced. The band rejection is realized by incorporating two co-directional split ring resonators (CSRR) on the radiator element. Switches are added to the CSRR structures to achieve the reconfigurability. The proposed antenna can operate at different switching states including a UWB state, single and dual band-notched states with good rejection behaviours. Good radiation patterns and gain values are also obtained for different switching states. This compact wideband antenna can be very good candidate for a wide range of mobile portable applications. A compact planar UWB-MIMO antenna (60 mm × 45 mm) is presented for wireless applications. The wideband isolation of more than 15 dB is achieved by etching a new trident-like slot on the ground plane of the antenna. An equivalent circuit have been introduced for analysis and the diversity performances are studied. The results show that the proposed MIMO antenna is a very good candidate for wireless applications. The study of these four special antennas has demonstrated that, using various techniques, the planar monopole antenna can be an excellent choice for a wide range of wireless communication applications

UWB Technology

Ultra Wide Band (UWB) technology has attracted increasing interest and there is a growing demand for UWB for several applications and scenarios. The unlicensed use of the UWB spectrum has been regulated by the Federal Communications Commission (FCC) since the early 2000s. The main concern in designing UWB circuits is to consider the assigned bandwidth and the low power permitted for transmission. This makes UWB circuit design a challenging mission in today's community. Various circuit designs and system implementations are published in this book to give the reader a glimpse of the state-of-the-art examples in this field. The book starts at the circuit level design of major UWB elements such as filters, antennas, and amplifiers; and ends with the complete system implementation using such modules

A Review on Different Techniques of Mutual Coupling Reduction Between Elements of Any MIMO Antenna. Part 1: DGSs and Parasitic Structures

This two-part article presents a review of different techniques of mutual coupling (MC) reduction. MC is a major issue when an array of antennas is densely packed. When the separation between the antennas i

A high bandwidth dimension ratio compact super wide band-flower slotted microstrip patch antenna for millimeter wireless applications

A compact high bandwidth ratio (BDR) super wide band flower slotted micro strip patch antenna (SWB-FSMPA) for super wide band (SWB) applications is presented. The SWB-FSMPA is constructed on a FR-4 substrate having a size of 16 × 22 mm2. The SWB-FSMPA incorporates a 50 Ω tapered micro strip line and a rectangular beveled defected ground structure (RB-DGS). This design enables a simulation bandwidth from 3.78 to 109.86 GHz, allowing for coverage of various wireless applications such as WiMAX (3.3–3.6 GHz), 5G (3.3–3.7 GHz), WLAN (5.15–5.825 GHz), UWB (3.1–10.6 GHz), Ku– (12–18 GHz), K– (18–27 GHz), Ka– (27–40 GHz), V– (40–75 GHz), and W– (75–110 GHz) millimeter wave bands. The SWB-FSMPA antenna exhibits a gain that varies within the range of 3.22–7.23 dBi and a peak efficiency of 93.3 %. The SWB-FSMPA possesses a bandwidth ratio (BR) of 29.1:1, a BDR of 5284 in the frequency domain, a minimal group delay (GD) fluctuation of <0.48 ns, and a linear phase in the time domain, making it well-suited for SWB applications

Multi-Fidelity Local Surrogate Model for Computationally Efficient Microwave Component Design Optimization

Publisher's version (útgefin grein)In order to minimize the number of evaluations of high-fidelity (fine) model in the optimization process, to increase the optimization speed, and to improve optimal solution accuracy, a robust and computational-efficient multi-fidelity local surrogate-model optimization method is proposed. Based on the principle of response surface approximation, the proposed method exploits the multi-fidelity coarse models and polynomial interpolation to construct a series of local surrogate models. In the optimization process, local region modeling and optimization are performed iteratively. A judgment factor is introduced to provide information for local region size update. The last local surrogate model is refined by space mapping techniques to obtain the optimal design with high accuracy. The operation and efficiency of the approach are demonstrated through design of a bandpass filter and a compact ultra-wide-band (UWB) multiple-in multiple-out (MIMO) antenna. The response of the optimized design of the fine model meet the design specification. The proposed method not only has better convergence compared to an existing local surrogate method, but also reduces the computational cost substantially.The National Natural Science Foundation of China Grant 61471258 and by Science & Technology Innovation Committee of Shenzhen Municipality Grant KQJSCX20170328153625183."Peer Reviewed

Feature Extraction from Reconfigurable Antenna

The work in this thesis concerns generic surrogate modelling techniques for a reconfigurable antenna based on any mechanisms. To make sure of the universality of the generic surrogate model, several new perspectives: related to field operating and circuit operating; feature extraction from the antenna; and reconfigurable antenna, are proposed to be a foundation and to provide guidance for the subsequent theory and applications. Additionally, the mathematical derivation of non-linear function fitting and the corresponding equivalent circuit/network is presented as the basic theory. Furthermore, three applications to corresponding antennas are presented to demonstrate the feasibility and effectiveness of the surrogate modelling techniques. Specifically, the first application contains two traditional antennas. They are a chassis antenna with two resonators and a band-notched ultra-wideband pyramidal monopole antenna. The second application to a frequency reconfigurable UWB antenna with a tunable notched-band is to obtain a data-driven surrogate model. The third application to the same reconfigurable UWB antenna is to obtain a physics-based surrogate model. In these applications, the surrogate modelling approach has many advantages. The approach is reliable and efficient. It has the flexibility for widespread use in many complicated scenarios, because of its elastic order and its adaptable weighting factor. It has fewer extracted parameters with better precision. These surrogate modelling techniques could be applied to integrate the reconfigurable antenna into a communication system. Furthermore, the approach could also be helpful in the microwave area auto design. Primarily, it could combine artificial intelligence (AI) algorithms to realize future wireless communication such as Smart Antenna, Software Defined Radio and Cognitive Radio. The novelty and contributions are summarized as follows: (1) This work proposes a completed systematic approach, including fundamental principles, rigorous mathematical derivation and feasible application verification. (2) The approach has the property of generalizability to cover all frequency reconfigurable antennas. (3) As a post-processing approach, it can convert the discrete data of CAD simulation and VNA measurement to a surrogate model with analytical function and equivalent circuit. (4) Some traditional antennas and reconfigurable antennas are taken as examples to demonstrate that the approach is feasible, effective, and precise. (5) The approach has the flexible ability to adapt to strict requirements and complicated scenarios

Diversified Fluid Antenna Designs for Mobile Communications

In current mobile communications, massive MIMO is an essential technology, especially for mm-wave 5G and future 6G mobile systems. However, implementing MIMO antennas for such applications is challenging due to the physical limitations of mobile devices. To address this issue, this study proposes novel surface wave-based fluid antennas. The proposed antennas achieve radiation pattern reconfigurability with a compact design of 10 mm x 33 mm 5 mm at a frequency range of 24 to 30 GHz, which is small enough for portable equipment. These antennas use only one feeding port, simplifying the feeding mechanism compared to MIMO systems that may require multiple RF chains. The fluid channel can also be easily scaled for different shapes and sizes with the proposed surface wave launcher. The proposed fluid antennas were simulated, fabricated, assembled, and measured within UCL facilities. Results show that these antennas achieve radiation pattern diversity, with an average RPDR (radiation pattern dynamic range) of up to 10 dB in the targeted mm-wave 5G frequency bands from 24 to 30 GHz. Radiation pattern dynamic range is a new indicator used to evaluate the proposed fluid antennas' radiation pattern reconfigurability. The proposed antennas offer several notable contributions. Firstly, they demonstrate the successful development of fluid antennas with radiation pattern reconfigurability. Secondly, the antennas feature a relatively simple structure, utilizing a 3D-printed container and PCB board, which enables cost-effective manufacturing and makes the antennas accessible to a wider range of users. Thirdly, the proposed fluid antenna incorporates a fluid control system and a comprehensive measurement setup specifically tailored for fluid antennas. These additions enhance the overall viability and practicality of the antenna design. Lastly, the introduction of the RPDR indicator provides a valuable tool for analyzing the radiation pattern reconfigurability of similar antennas. This indicator facilitates performance comparisons and aids in the refinement of future antenna designs

Rectennas for RF wireless energy harvesting

There is an increasing interest in energy harvesting. The rectenna, which is a combination of a rectifier and an antenna, is a device to harvest wireless energy in the air. This thesis is concentrated on the analysis, design and measurement of compact rectennas for radio frequency (RF) wireless energy harvesting applications, and the thesis can be divided into three parts. The first part is about broadband planar dipole antennas with an unidirectional radiation pattern which is suitable for wireless energy harvesting applications. With the rapid development of various wireless systems, there is a need to have a broadband rectenna for energy collection. The antenna is optimized by changing the dipole shape, diameter, feed gap and the spacing between the antenna and the ground plane. It is shown the optimized antenna has a broad (from 2.8 to at least 12 GHz) with the ability to produce unidirectional radiation pattern. It is a good candidate to form a wideband dual-polarized antenna array for applications such as the wireless power transmission and collection. In addition, a simple rectenna and duel-polarized rectenna arrays are presented. The measurement of the rectenna array is shown that the design has produced the desired DC power with reasonable efficiency. The study is confirmed that the more elements in the array, the higher output voltage although the bandwidth is not as wide as expected because of practical limits. The second part is about a novel wideband cross dipole rectenna for RF wireless energy harvesting. The proposed device consists of a cross dipole antenna, low-pass filter (LPF) and voltage doubling rectifier circuit using Shottcky diodes as rectifying elements. It works over the frequency range from 1.7 to 3 GHz for the reflection coefficient less than -10 dB. Besides, the proposed rectenna can convert the RF energy into DC energy with a good conversion efficiency of up to 75% for high input power density levels (>5 mW/cm^2). In addition, another wideband rectenna built on FR4 substrate is optimized for low input power and the rectenna is optimized, built and measured. A further investigation for the input impedance of rectifier is also conducted. Experimental results demonstrate the rectenna has wideband rectification performance and the maximum rectenna conversion efficiency at 1.7 GHz is more than 50% for the power density of 0.1 mW/cm^2. The third part is about improving rectenna conversion efficiency for low input power density. Increasing the rectenna conversion efficiency for low power density is significant for improving rectenna performance. Currently, there are few of research focused on wideband rectenna arrays for low input power. A new wideband rectenna array with a reflector is developed to increase the rectenna conversion efficiency and output voltage through increasing the gain of the antenna. In addition, two connection methods are used to build the rectenna array and advantages and disadvantages for each method are presented. The RF to DC conversion efficiency of proposed rectenna arrays is much improved for low input power density over a wide bandwidth. This research has produced some important designs and results for wireless energy harvesting, especially in wideband rectennas, and is a solid step towards possible widespread applications of rectennas in the near future

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen