Negative Group Delay Devices: From concepts to applications
Negative Group Delay Devices: From Concepts to Applications introduces the theoretical concept, analysis, design methodology and implementation of negative group delay (NGD). The NGD concept is a recent topic in electrical and electronic engineering research based on an unconventional function; the generation of an output signal seemingly in timeadvance of the input signal. The NGD function has been exploited to develop experimental highperformance electronic devices, and novel design features of radio frequency (RF) and microwave electronic devices, such as filters, power dividers and amplifiers. Examples include the realization of nonFoster reactive elements, shortening or reducing delay lines, enhancing the efficiency of feedforward linear amplifiers, improvement of phase shifters accuracy and bandwidth, equalization of electrical interconnect effects for the microwave, digital and mixed signal integrity improvement, and minimizing beamsquint in seriesfed antenna arrays. The aim of the book is to advance understanding of the NGD principle and its applications. Recent results and outcomes for the different methodologies used to elaborate the NGD function are shared in each chapter, and approaches relevant to various devices are described. This book will be of particular interest to researchers, academics and postdoctoral students interested in signal processing in electronic, radio frequency, microwave and optoelectronic devices, and particularly those investigating unconventional circuit and system design.
Inspec keywords: power dividers; printed circuits; active networks; passive networks; microwave circuits; noise; recursive filters; microstrip circuits; waveguide couplers; microwave amplifiers; resonators; dispersive channels; microstrip lines; microwave metamaterials; delay circuits
Other keywords: nonFoster elements; detectable information; hybrid couplerbased NGD circuit; superluminality information; NGDbased Hilbert filter; active NGD distributed circuits; negative group delay power dividers; microwave transversal NGD circuits; metamaterialbased commonmode noise filter; negative group delay devices; recursive filterbased NGD circuits; dispersive channels; negative group velocity; multilayer PCB; microwave amplifierbased active lumped NGD devices; NGD effect; passive distributed NGD distributed circuits; splitring resonatorloaded Xband waveguide; microstrip line negative group delay circuits; delayinduced NGD
Subjects: Printed circuits; Amplifiers; General electrical engineering topics; Microwave circuits and devices; Filters and other networks; Waveguide and microwave transmission line components
 Book DOI: 10.1049/PBCS043E
 Chapter DOI: 10.1049/PBCS043E
 ISBN: 9781785616402
 eISBN: 9781785616419
 Page count: 375
 Format: PDF

Front Matter
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1 Microstrip line negative group delay circuits and applications to communication systems
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In this chapter, a synthesis of microstrip line negative group delay (NGD) circuits is presented. Microstrip line resonators are considered for designing various topologies of transmission and reflectiontype NGD circuits. Similarly, the defected microstrip line structures such as defected ground structure (DGS) and defected microstrip structure (DMS) are also used to synthesize the transmissiontype NGD circuits. In addition, a filter synthesis based on finite unloadedquality factor resonators is also presented to design NGD circuit with the arbitrarily prescribed group delay. Finally, the applications of NGD circuit in communication systems are explored. The applications of NGD circuit include the efficiency enhancement of feedforward amplifier and bandwidth enhancement of analog feedback amplifier.

2 Negative group delay power dividers
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Power dividers have been widely adopted as basic building components in microwave circuits and systems and extensively studied over the past decades including the unequal and tunable power division ratio, circuit miniaturization, and multiband operation. Because the group delay (GD) can influence the performances of RF/electronic circuits and systems, understanding the effect of GD has become critical for communication systems. However, GD analysis of power divider has rarely been considered in previous works and the positive GDs have only been provided through different transmission paths. In this chapter, several topologies of power divider and coupler with the predefined NGD characteristics will be presented including equal and unequal power division ratios. Similarly, coupling matrix synthesis with finite unloadedquality resonators will be also presented in this chapter to design the power divider with the predefined NGD.

3 Delayinduced negative group delay
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Realtime prediction of signals is one of the most fundamental tasks encountered in control problems, in machine learning and artificial intelligence applications, as well as by living systems. It is known that the phenomenon of negative group delay (NGD) can be utilized to perform realtime prediction of smooth input signals. In the present contribution, it is first shown that a particular system property that can cause an NGD is timedelayed feedback. Based on this insight, very simple linear signal predictors that use past predicted, or feedback, values rather than past signal values for prediction are presented. These delayinduced negative group delay (DINGD) predictors exist both for discreteand continuoustime signals and afford realtime prediction of complex signals without the need for a specific signal model. The theory of DINGD predictors is outlined and demonstrated on various types of broadband input data simulations. As an example for a technical application, an algorithm is presented that predicts, in real time, smooth voluntary manual movements of a computer mouse or stylus. In general, manufactured or natural systems utilizing the DINGD predictor would not require a memory of input signal values but only of already predicted, internalized states. Along this line, there is evidence for the significance of DINGD prediction in biological systems, including the human motor system. Finally, the DINGD predictor as a special type of prediction by anticipatory coupling is discussed.

4 Microwave transversal and recursive filterbased negative group delay circuits and nonFoster elements
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This chapter presents some latest developments in microwave transversal and recursive filterbased negative group delay (NGD) circuits as well as their applications in realizing nonFoster elements. By using transversal and recursivefilter approaches, the desired amount of NGD can be synthesized with enhanced bandwidth. The fully distributed topology of the proposed NGD circuits makes it feasible to scale up to higher frequency ranges such as millimeter waves. In addition, it is demonstrated that the transversalfilterbased NGD circuit can realize nonFoster elements with unconditional stability, enabling a new approach to realizing stable nonFoster elements.

5 Hybrid couplerbased NGD circuit
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A theory of negative group delay (NGD) topology based on hybrid coupler is investigated. It acts as a passive microwave circuit topology. The NGD cell under study is constituted by a hybrid coupler with one of the output and isolated access ways connected in feedback. The feedback circuit is constituted by a lossy transmission line (TL). Two configurations of cells with interconnected isolatedcoupled and isolateddirect accesses are investigated. The equivalent Sparameter model of the proposed structure is established. It is derived mathematically that the fully distributed hybrid couplerbased topology is susceptible to exhibit NGD phenomenon. The fundamental properties of the innovative NGD topology as the NGD levelbandwidth product are formulated. The synthesis relations enabling to determine the NGD circuit parameters in function of the desired NGD value are extracted. The relation between the NGD level and the insertion loss is elaborated. Parametric numerical analyses in function of the TL attenuation and time delay were performed. The NGD concept feasibility is highlighted by a very good correlation between the theoretical calculation and the numerical simulations. In addition, the NGD phenomena were also occurred with the consideration of microstrip lines in feedback with 90°and 180°hybrid couplers. The NGD topology under study is potentially useful for the signal delay correction in the RF system.

6 NGDbased Hilbert filter
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A particular application of the negative group delay (NGD) for a particular function of independent frequency phase shifter (PS) is developed in the present chapter. The independent frequency PS is a quadrature and unity magnitude PS which is known as Hilbert filter. An original circuit theory on analog Hilbert filter dedicated to the RF/microwave application is established in this chapter. The Hilbert filter can be assumed as an independent frequency quadrature PS with magnitude equal to unity. The identification methodology of the simplest lumped elementbased topologies is presented. The proposed elementary cells are based on the NGD active cell constituted by a field effect transistor in cascade with a shunt RLCseries network. This NGD circuit is cascaded with a positive group delay (PGD) passive network in order to synthesize an Hilbert filter around the targeted operating frequency. The analytical expressions enable to establish the Hilbert filter designability characteristic condition between the topological parameters. The synthesis relations of the identified cells are established. The characteristics and properties are developed. Application example with the identified topology of LC and NGD cells in cascade is presented. The microwave Hilbert filter concept feasibility is demonstrated. Three proofs of concept (POCs) circuit operating around 2.45 GHz were synthesized and designed. After Sparameter simulations, transmission phase 90 + 10 flatness's are generated within the relative frequency better than 50% and +1 dB gain flatness's within 20% bandwidth. The identified Hilbert filter cells functioning are validated with simulations of SPICE environment designed circuits. As expected, typically narrow band Hilbert filters were obtained. The developed analog Hilbert filter topology is potentially useful for the RF/microwave transceiver system architecture designs notably for image intermediate frequency rejection.

7 Design technique on the microwave amplifierbased active lumped NGD devices
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This chapter addresses a microwave circuit theory on the negative group delay (NGD) principle. The characterization methodology of this unfamiliar NGD function is described. The basic NGD topologies are typically active cells composed of RF lownoise amplifier (LNA). Typically, lowpass NGD topologies are identified and characterized. The lowpass NGD circuits consisted of simple firstorder RLseries and RCparallel networks. Similar to the filter theory, bandpass NGD circuits are introduced from lowpass to bandpass transform. The proposed NGD circuit theory is established on the Sparameter approach. The proposed NGD topology main characteristics and properties as the NGD level, cutoff frequencies or bandwidth, central frequency and figureofmerit are established. Given the LNA Sparameter model, the NGD synthesis and design method of the lowand bandpass NGD cells in function of the specified NGD values is presented. The NGD cell parameter calculations in function of the expected NGD level, insertion loss and reflection coefficient are introduced. NGD proof of concept (PoC) are synthesized, designed and simulated in order to understand and validate the proposed NGD lowpass and bandpass functions. As expected, lowpass and bandpass NGD aspects are obtained. The lowpass NGD circuits present NGD level of about 2 ns over the bandwidth of about 70 MHz. Then, bandpass NGD circuits was synthesized to operate at about 0.5 GHz over the bandwidth of about 140 MHz with NGD level of about 4 ns. It is worth mentioning that the NGD circuits respect the requirements of RF and microwave specifications.

8 Limits of passive and active negative group delay distributed circuits
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The chapter examines the negative group delay (NGD) limits of active and passive distributed element transmission line circuits. The first section illustrates NGD characteristic examples in both frequency and time domains, and pertinent figure of merits and tradeoffs which can be used to evaluate performance of different NGD devices. The relationship between the timedomain transients and outofband gain will be analyzed and discussed in the context of modulated signals. The second section introduces resonatorbased circuit NGD topologies and shows how active elements are employed for gain compensation. In the third section, the asymptotic limits of these circuits are then derived while considering issues of gain, bandwidth, inband distortion, and outofband gain. The final section will extend the theory to NGD phenomena in general linear causal media, derived from KramersKronig relations. Experimental results of fabricated designs demonstrating the concepts will be put forward throughout the chapter.

9 Superluminality and detectable information in dispersive channels
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Energy exchange between an electromagnetic pulse and dispersive media may result in complicated, yet interesting, phenomena in which the group velocity becomes abnormal (i.e., superluminal or negative). For such cases, signal velocity (velocity of detectable information) remains debatable. In this chapter, we present a systematic study that can be applied to pulse propagation in any dispersive medium in order to quantify the detectable information content and calculate its speed, while accounting for pulse reshaping effects and noise generated in the medium and the detector. Accordingly, we present an operational context within which the constraints of superluminal signaling and its potential applications are shown. We provide scenarios in which the signal velocity is evaluated in microwave circuits with negative group delays and extend the method to include optical pulses in inverted media as well. Such analysis explores the fundamental limitations and capabilities of a broad range of superluminal signaling applications.

10 Splitring resonatorloaded Xband waveguide supporting negative group velocity
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Analytical discussions and experimental results are presented for an Xband (8.212.4 GHz) waveguide loaded with an array of splitring resonators (SRR) designed to exhibit negative group delay and negative refractive index in the 2.83.6 GHz frequency range, thus below the cutoff frequency (6.557 GHz) of the empty waveguide. Negativegroupvelocity effects arise from resonant absorption losses of the splitrings, whereby such effects are demonstrated by timedomain simulations of propagating modulated Gaussian pulses. It is shown that an injected pulse of 80ns time width and central frequency of 3.26 GHz experiences a negative delay of 14 ns after traversing the waveguide while retaining its Gaussian shape although with strong attenuation. A retrieval procedure is used to determine the complex propagation factor for which the role of the attenuation constant in reshaping the output spectrum amplitude is discussed. The SRRloaded waveguide examined here has attractive features, as the system is easily scalable to higher frequencies and proves to show potential applications for the delay compensations of signal in microwave waveguide systems by keeping a constant group delay to avoid signal distortion.

11 Metamaterialbased commonmode noise filter with NGD effect for multilayer PCB
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The ever increase of data transmission rate that runs to tens Gb/s or beyond in the highspeed electronic circuits nowadays makes commonmode noise become a critical issue that could introduce electromagnetic interference (EMI) and adversely affect signal integrity (SI) and power integrity (PI). Together with miniaturization requirement of circuit design, it becomes requisite to explore newly effective commonmode filtering technology to tackle the commonmode noise associated EMI problems. In this chapter, the metamaterialbased commonmode filter design is elaborated. Through the study of a set of compact planar commonmode filters using defected ground structure (DGS), the fundamental filtering methodology and equivalent circuit models are elucidated with the presence of reasonable insertion loss performance. One of the intrinsic characteristics of the filters, termed negative group delay (NGD), has yet been paid much attention before, is also evaluated and discussed in this chapter for addressing SI/PI and EMI issues in electronic circuits.

Back Matter
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