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

The Effect of Impedance Mismatch on Phase Linearity of GCPW Loaded Transmission Lines and Shunt Stubs

This paper presents a study on the effect of impedance mismatch on phase linearity (group delay variations) in grounded coplanar waveguide (GCPW) structures. Two 400 ps GCPW delay lines were designed using a short circuited stub and a trans- mission line. The structures were simulated over a wide frequency range (0.1 GHz- 5 GHz) using both ADS circuit model and CST electromagnetic simulation tool. Based on mathematical analysis and simulation results, impedance mismatch appears to have a large e_ect on group delay variations in stubs when compared to transmission lines. The simulated time delay of the short circuited stub shows a maximum delay deviation of ±0.75% and ±7.4% for 1.6% and 5.8% impedance mismatch values, respectively. On the other hand, the transmission delay line simulation results show only ±0.1% and ±1.5% for the same impedance mismatch. For the electromagnetic simulation, the presented results indicate even larger variation of time delay for GCPW short stub as it reaches ±3.75% and ±7.5% at 2 GHz and 4.5 GHz for 1.6% impedance mismatch, respectivel

A COMPREHENSIVE OVERVIEW OF RECENT DEVELOPMENTS IN RF-MEMS TECHNOLOGY-BASED HIGH-PERFORMANCE PASSIVE COMPONENTS FOR APPLICATIONS IN THE 5G AND FUTURE TELECOMMUNICATIONS SCENARIOS

The goal of this work is to provide an overview about the current development of radio-frequency microelectromechanical systems technology, with special attention towards those passive components bearing significant application potential in the currently developing 5G paradigm. Due to the required capabilities of such communication standard in terms of high data rates, extended allocated spectrum, use of massive MIMO (Multiple-Input-Multiple-Output) systems, beam steering and beam forming, the focus will be on devices like switches, phase shifters, attenuators, filters, and their packaging/integration. For each of the previous topics, several valuable contributions appeared in the last decade, underlining the improvements produced in the state of the art and the chance for RF-MEMS technology to play a prominent role in the actual implementation of the 5G infrastructure

Development of Tunable RF Integrated Passive Devices

Radio frequency (RF) lumped elements are crucial building blocks for designing any type of passives circuits for RF front-end applications in mobile devices. In particular, high-quality (Q) factor lumped elements are desirable for improving both insertion loss and noise performance. Integrated passive devices (IPD) technology is a platform that can provide miniature inductors, and capacitors with high- Q values that are unattainable with traditional CMOS technologies. Over the past several years, IPD technology has been used to implement devices such as filters, couplers and impedance-matching networks for a wide range of system-in-package applications. However, most of the IPD circuits do not yet have any tunable/reconfigurable functions for use in frequency agile applications. The objective of this research is to develop tunable integrated passive devices (IPDs) using barium strontium titanate (BST) and micro-electrical-mechanical-systems (MEMS) technologies. Another objective is to develop a fabrication process for monolithic integration of MEMS switches and IPD devices. A 4-mask IPD glass/alumina-based fabrication process is developed at the University of Waterloo for the first time. Details of the modeling and characterization of high-Q lumped elements, L and C, are investigated. The RF performance of these elements is compared with that of similar designs fabricated in a commercial IPD foundry. To highlight the benefits of the IPD process, lumped element bandpass filters are designed, fabricated, and tested. BST varactors are integrated with IPD circuits to demonstrate a highly miniaturized tunable impedance matching network featuring a wide impedance coverage from 2-3 GHz and an insertion loss of approximately 1 dB. The network promises to be useful in a broad range of wireless applications. A high performance tunable IPD/BST bandstop filter with a wideband balun as a multichip module is also proposed. Reconfigurable IPD/BST bandpass filters with tunable transmission zeros are presented and investigated experimentally for operation under high power levels. Intermodulation test results are presented for the integrated IPD/BST devices. Making use of the fact that the IPD fabrication process is amenable to the realization of MEMS devices, the IPD process originally developed for realizing passive circuits is further expanded to accommodate monolithic integration of MEMS switches with IPD circuits. Contact-type MEMS switches are developed, fabricated and tested. Also, a monolithically integrated IPD/MEMS 3-bit high resolution true-time delay network and high-Q switched-capacitor bank are fabricated and tested to demonstrate the benefits of integrating MEMS technology with the IPD technology

Electronically reconfigurable wideband microwave filters

Many systems require multi function capability in the filter aspects of systems; the method currently used is filter banks which take up a lot of board space. It is thought that reconfigurable filters hold the key to replacing filter banks in order to save board space and thus potentially increasing functionality of the systems. The aim of this research is to develop electronically reconfigurable microwave filters for future communication systems. The project investigates some key design issues of reconfigurable filters. Circuits were modelled and full-wave electromagnetic simulations were performed for the investigation. Experimental work was carried out to demonstrate advanced reconfigurable microwave devices. The components used in each concept investigated were pin diodes due to their superior performance in wideband and high frequency applications. Firstly a single coupled line concept was looked at for bandwidth reconfigurability. This concept was then further developed for industrial applications by simply cascading these sections to obtain a high selective filter. A design method was developed for any number of cascades both with and without an impedance transformer; the use of LCP was used to increase flexibility due to its desirable characteristics. The most desirable outcome would be filter to simultaneously control bandwidth and frequency. In order to tackle this issue the coupled line concept was adapted to incorporate frequency tunability, along with a design method being presented. Furthermore, a cascaded highpass/ lowpass filter was also explored for this concept for added flexibility in the design of a filter capable of control of both bandwidth and center frequency

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

Radio Frequency Microelectromechanical Systems in Defence and Aerospace

For all onboard systems applications, it is important to have very low-loss characteristics and low power consumption coupled with size reduction. The controls and instrumentation in defence and aerospace continually calls for newer technologies and developments. One such technology showing remarkable potential over the years is radio frequency microelectromechanical systems (RF MEMS) which have already made their presence felt prominently by offering replacement in radar and communication systems with high quality factors and precise tunability. The RF MEMS components have emerged as potential candidates for defence and aerospace applications. The core theme of this paper is to drive home the fact that the limitations faced by the current RF devices can be overcome by the flexibility and better device performance characteristics of RF MEMS components, which ultimately propagate the device level benefits to the final system to attain the unprecedented levels of performance.Defence Science Journal, 2009, 59(6), pp.568-567, DOI:http://dx.doi.org/10.14429/dsj.59.156

Synthesis, design, and fabrication techniques for reconfigurable microwave and millimeter-wave filters

As wireless communication becomes increasingly ubiquitous, the need for radio receivers which can dynamically adjust to their operating environment grows more urgent. In order to realize reconfigurable receivers, tunable RF front-end components are needed. This dissertation focuses on the theory, design, and implementation of reconfigurable microwave and millimeter-wave filters for use in such receivers. First, a theoretical framework is developed for absorptive bandstop filters, a new class of bandstop filters which overcomes some of the limitations of traditional tunable bandstop filters caused by the use of lossy tunable resonators. This theory is used in conjunction with silicon-micromachining fabrication technology to realize the first ever tunable bandstop filter at W-Band frequencies, as well as a state-of-the-art Ka-band tunable bandstop filter. The problem of bandwidth variation in tunable filters is then addressed. Widely-tunable filters often suffer from variations in bandwidth, excluding them from many applications which require constant bandwidth. A new method for reducing the bandwidth variation of filters using low-loss evanescent-mode cavity resonators is presented, and this technique is used to realize up to 90% reduction of bandwidth variation in octave-tunable bandstop filters. Lastly, a new differential coupling structure for evanescent-mode cavity resonators is developed, enabling the design of fully-balanced and balanced-to-unbalanced (balun) filters. An octave-tunable 3-pole bandpass balun filter using this coupling structure is presented. The balun filter has excellent amplitude and phase balance, resulting in common-mode rejection of greater than 40 dB across its octave tuning range

Synthesis, design, and fabrication techniques for reconfigurable microwave and millimeter-wave filters

As wireless communication becomes increasingly ubiquitous, the need for radio receivers which can dynamically adjust to their operating environment grows more urgent. In order to realize reconfigurable receivers, tunable RF front-end components are needed. This dissertation focuses on the theory, design, and implementation of reconfigurable microwave and millimeter-wave filters for use in such receivers. First, a theoretical framework is developed for absorptive bandstop filters, a new class of bandstop filters which overcomes some of the limitations of traditional tunable bandstop filters caused by the use of lossy tunable resonators. This theory is used in conjunction with silicon-micromachining fabrication technology to realize the first ever tunable bandstop filter at W-Band frequencies, as well as a state-of-the-art Ka-band tunable bandstop filter. The problem of bandwidth variation in tunable filters is then addressed. Widely-tunable filters often suffer from variations in bandwidth, excluding them from many applications which require constant bandwidth. A new method for reducing the bandwidth variation of filters using low-loss evanescent-mode cavity resonators is presented, and this technique is used to realize up to 90% reduction of bandwidth variation in octave-tunable bandstop filters. Lastly, a new differential coupling structure for evanescent-mode cavity resonators is developed, enabling the design of fully-balanced and balanced-to-unbalanced (balun) filters. An octave-tunable 3-pole bandpass balun filter using this coupling structure is presented. The balun filter has excellent amplitude and phase balance, resulting in common-mode rejection of greater than 40 dB across its octave tuning range