Miniaturised and reconfigurable planar filters for ultra-wideband applications

An increasing demand for electromagnetic spectrum has resulted from the emergence of feature-rich and faster throughputs wireless applications. This necessitates the developments of dynamic reconfigurable or multifunctional systems to better exploit the existing spectrum. Future wireless devices will be expected to communicate over several bands with various other devices in order to fine tune the services they provide to the user. Each band may require a separate RF transceiver and such modern wireless multi-band multi-mode communication systems call for high performance, highly integrated compact modules. Since the Federal Communications Commission (FCC) released the unlicensed frequency band 3.1-10.6 GHz for ultra-wideband (UWB) commercial communications, the development race for commercialising UWB technology has seen a dramatic increase around the world. The aim of this research is to develop reconfigurable planar microwave filters for ultrawideband applications. The project investigates some key design issues of reconfigurable filters, which are being observed constantly in the latest development and realisation of microwave filters. Both analytical and numerical methods are performed to construct a realistic and functional design. Two different types of frequency reconfigurability are investigated in this thesis: discrete (e.g. PIN diode, Optical switch) and continuous (e.g. varactor diode). Using the equivalent circuits and considering the direct coupled filter structure in most cases, several topologies with attractive features are developed for future communication systems. The proposed works may be broadly categorised into three sections as follows. The first section explores a square ring shape close loop resonator along with an opencircuited stub in the symmetry plane. To realise a reconfigurable frequency states within the same spectrum, an innovative approach is developed for this case. An optical or photoconductive switch, comprised of a silicon die activated using near infrared light is investigated as a substitute of PIN diode and performances are evaluated to compare the feasibilities. In addition, a in-band interference rejection technique via externally coupled Tshape resonator is shown. However, it is observed that both structures achieve significant size reductions by utilising the inner part of the resonators. To improve the filter selectivity, a convenient design approach generating a pair of transmission zeros between both passband edges and a single zero in the stop band for harmonic suppression is discussed in the second section. Moreover, the development of notched rejection bands are studied and several novel methods to create a single and multiple notched bands employing the square ring shape structure are proposed. On inspection, it is found that the notch structure can be implemented without deteriorating the filter performances. The discussions are supplemented with detailed design examples which are accompanied by theoretical, simulated and experimental results in order to illustrate the filter development process and showcase practical filter performance. The third section reveals a novel highly compact planar dual-mode resonator with sharp rejections characteristics for UWB applications. A bandwidth reconfiguring technique is demonstrated by splitting its even-mode resonance. Filter structure with the dual-mode resonator is shown to have a relatively wide tuning range, significantly low insertion loss and a constant selectivity along with frequency variations in comparison to similar published works. Finally, the earlier dual-mode structure are modified to realise a dual wideband behaviour. A detail analysis with comprehensive design procedures is outlined and a solution for controlling the frequency bandwidths independently according to the application interest is provided. In line with the previous section, experimental verification is presented to support and supplement the discussions

An Overview of Filter Integrated Switch (FIS) for RF and Microwave Applications

Integrating multiple devices into one single device is an effective method to reduce circuit size, mismatching loss, and fabrication cost. Radio frequency (RF) and microwave device integrated with filter have become a popular design concept in the recent years. In this paper, an overview of the filter integrated switch (FIS) for RF and microwave applications is presented based on previously published studies and research journals starting from 2006 until 2016. This paper also emphasizes the use of previous and current development of filter integrated switches which mainly covers the fundamental concept on the FIS, the research trends in designs and developments. At the end, this paper reports on the variety of applications that can greatly benefit from FIS and some challenges and factors that need to be considered in designing and development of filter integrated switches

Synthesis Technique of Thickness-Customizable Multilayered Frequency Selective Surface for Plasma-Based Electromagnetic Structures

This dissertation provides a synthesis technique for the design of thickness-customizable high-order (N ≥ 2) bandpass frequency selective surface (FSS) and its application in realizing versatile multi-layered FSS and absorbers. Admittance inverters layers are used to synthesize the transfer response of the filter given desired characteristics such as filter type, center frequency, and bandwidth. These inverter layers are essentially electromagnetic coupling interlayers that can be adjusted to customize the thickness of multilayered FSS without degrading the desired filter performance. A generalized equivalent circuit model is used to provide physical insights of the proposed design. This synthesis technique is adopted to deliver a versatile implementation capability of high-order FSS filters using various dielectric spacers with arbitrary thicknesses. Such technique enables the realization of spatial filters with variable size, while maintaining the desired filter response. To highlight the significance of the proposed synthesis technique, its concept is applied to two practical problems including the design of compact switchable FSS and adaptive/tunable microwave absorbers as it may allow simpler integration of active components that require specific physical dimensions. In the first practical problem, the feasibility of deploying plasma switchable compact spatial filter in harsh electromagnetic radiation environments is investigated. The proposed FSS integrates contained plasma (plasma-shells) as active tuning elements. These ceramic, gas-encapsulating shells are ideal for high-power microwave and electromagnetic pulse protection because they are rugged, hermetic, operable at extreme temperatures, and insensitive to ionizing radiation. A 2D periodic second-order switchable spatial filter is implemented. It is composed of electrically small Jerusalem cross structures embedded with discrete plasma shells strategically located to effectively switch the transfer function of the filter. This technique is used to realize compact low profile second order band pass spatial filter operating at S-band. It also has the ability to switch its transfer function within 20 to 100 ns while enabling in-band shielding protection for aerospace or terrestrial electromagnetic systems subjected to high power microwave energy (HPME) and high electromagnetic pulse (HEMP) in harsh space environment. Experimental results are shown to be in good agreement with simulation results. The second practical problem is addressed by deploying a large-scale adaptable compressed Jaumann absorber for harsh and dynamic electromagnetic environments. The multilayered conductor-backed absorbers are realized by integrating ceramic gas-encapsulating shells and a closely coupled resonant layer that also serves as a biasing electrode to sustain the plasma. These active frequency selective absorbers are analyzed using a transmission line approach to provide the working principle and its frequency tuning capability. By varying the voltage of the sustainer, the plasma can be modeled as a lossy, variable, frequency-power-dependent inductor, providing a dynamic tuning response of the absorption spectral band. To study the power handling capability of the tunable absorber, dielectric and air breakdowns within the device are numerically emulated using electromagnetic simulation by quantifying the maximum field enhancement factor (MFEF). Furthermore, a comprehensive thermal analysis using a simulation method that couples electromagnetics and heat transfer is performed for the absorber under high power continuous microwave excitations. The maximum power level handling capability of the microwave absorber has been numerically predicted and validated experimentally

Reconfigurable and multi-functional antennas

This thesis describes a research into multi-frequency and filtering antennas. Several novel antennas are presented, each of which addresses a specific issue for future communication systems, in terms of multi-frequency operation, and filtering capability. These antennas seem to be good candidates for implementation in future multiband radios, cognitive radio (CR), and software defined radio (SDR). The filtering antenna provides an additional filtering action which greatly improves the noise performance and reduces the need for filtering circuitry in the RF front end. Two types of frequency reconfigurable antennas are presented. One is tunable left-handed loop over ground plane and the second is slot-fed reconfigurable patch. The operating frequency of the left handed loop is reconfigured by loading varactor diodes whilst the frequency agility in the patch is achieved by inserting switches in the coupling slot. The length of the slot is altered by activating the switches. Compact microstrip antennas with filtering capabilities are presented in this thesis. Two filtering antennas are presented. Whilst the first one consists of three edge-coupled patches, the second filtering antenna consists of rectangular patch coupled to two hairpin resonators. The proposed antennas combine radiating and filtering functions by providing good out of band gain suppression

A Recent Approach towards Fluidic Microstrip Devices and Gas Sensors: A Review

This paper aims to review some of the available tunable devices with emphasis on the techniques employed, fabrications, merits, and demerits of each technique. In the era of fluidic microstrip communication devices, versatility and stability have become key features of microfluidic devices. These fluidic devices allow advanced fabrication techniques such as 3D printing, spraying, or injecting the conductive fluid on the flexible/rigid substrate. Fluidic techniques are used either in the form of loading components, switching, or as the radiating/conducting path of a microwave component such as liquid metals. The major benefits and drawbacks of each technology are also emphasized. In this review, there is a brief discussion of the most widely used microfluidic materials, their novel fabrication/patterning methods

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.Comment: 16 pages, 12 figure

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

Miniaturized High-Q Tunable RF Filters

This dissertation focuses on the investigation and development of novel efficient tuning techniques and the design of miniaturized high-Q tunable RF filters for high-performance reconfigurable systems and applications. First, a detailed survey of the available tuning concepts and state-of-art tunable filters is provided. Then, a novel so-called inset resonator configuration is presented for the applications of fixed and tunable coaxial filters. The design procedure of frequency tunable filters with constant absolute bandwidth (CABW) is described, and various tunable inset filters are implemented, offering many desirable merits, including the wide tuning range and stable high-Q with minimum variation. For wide octave frequency tuning ranges with CABW, a second novel concept is presented using so-called re-entrant caps tuners. Beside simplicity and compactness, this technique also features enhanced spurious performance and wider tuning capabilities than the conventional means. Also, in this dissertation, various miniaturized reconfigurable dual-band/dual-mode bandpass filters and diplexers are presented using compact dual-mode high-Q TM-mode dielectric resonators. Furthermore, a novel microfluidic-based ultra-wide frequency tuning technique for TM010-mode dielectric resonators and filters is introduced in this dissertation. In addition to the very wide tuning window, this mechanism has key advantages of low-cost, simplicity, and intrinsic switch-off. Lastly, the dissertation includes a novel bandwidth reconfiguration concept with multi-octave tuning using a single element for coaxial bandpass filters. This mechanism brings many features including the fast tuning, constant high-Q, intrinsic switch-off, and wide BW-reconfiguration