Negative Group Delay Research Articles

Stop-band type NGD RLC-resonant circuit sensitivity analysis

This paper investigates on the rarely studied negative group delay (NGD) RF circuit with innovative stop-band (SB) behavior. In difference with the classical filter, the SB-NGD function is identified in function of frequency bands where the group delay (GD) presents negative sign. The ideal diagram specifying the SB-NGD function is introduced by indicating all the appropriate parameters. The S-parameter analytical model of the circuit is established. The SB-NGD analysis is developed. The main specifications of the SB-NGD circuit are expressed in function of its constituting components. Then, the design synthesis equations enabling to determine the SB-NGD circuit in function of the desired specifications as the center frequency and GD are built up. To illustrate concretely the feasibility of the SB-NGD function, a circuit proof-of-concept composed of LC-series network is theoretically analyzed. A parametric analysis on the SB circuit elements is accomplished to appraise the influence of each element on the SB-NGD specifications. To validate the unfamiliar SB-NGD theory, a prototype is fabricated and tested. The GD measured response of the considered circuit is compared by simulations and analytical calculations. SB-NGD responses showing a good agreement between the calculation and simulation are obtained with a 15 MHz center frequency, 44 ns GD and 3 MHz bandwidth.

Systematic design of negative group delay circuits

In this brief, we introduce and verify some general opamp based structures to obtain negative group delay circuits. First order and second order negative group delay circuits are verified and all are noninverting circuits. As both the transfer functions and the group delay are simultaneously considered important derivations related to the actual bandwidth of operation are derived. LTSpice circuit simulations and experimental results using Gaussian input signals are provided to verify the theory.

Single CFOA-based active Negative Group Delay circuits for signal anticipation

The group delay of a signal prior to data monitoring is a crucial consideration in today’s real-time applications, especially for those that involve long sensor arrays or high-order filters. In this article, nine new second-order Negative Group Delay (NGD) circuits based on Current Feedback Operation Amplifier (CFOA) are proposed, and their transfer functions are demonstrated. These circuits have a wide range of applications, from audio to mechanical signals and sensor signal anticipation. An example design procedure is provided for one of the introduced circuits. A time-domain analysis is performed using both a single-tone sinusoidal and a band-limited audio recording in the frequency range of 1 Hz to 500 Hz. The article assesses the change in the signal using Root Mean Square Error (RMSE) and cross-correlation. Furthermore, the relationship between the NGD value and the operation range of the circuit is investigated and verified experimentally. The results show that an NGD value of approximately 100μs can be achieved with an amplitude error of 0.86% for a single-tone input and 1.54% for an audio recording, and an operation range of about 650 Hz.

Planar Coupled-Line-Based Flat Negative Group Delay Microwave Circuit With Size Reduced and Bandwidth Enhanced

Planar Coupled-Line-Based Flat Negative Group Delay Microwave Circuit With Size Reduced and Bandwidth Enhanced

COVID-19 cases prediction with negative group delays digital function

The negative group delay (NGD) is an uncommon function enabling to propagate arbitrary waveform signals with time-advance behavior. The counterintuitive NGD function was initially experimented for anticipating typically fast and short duration electronic signals in micro- and milli-second time scale. The application of NGD function to large time scale signal attracts more and more the attention of data processing engineer. This paper aims to investigate on the ability of NGD function to predict time- dependent social data with someday time-advances. As practical case of study, an innovative application of NGD function for predicting disease cases is treated. The digital circuit theory enabling to understand the low-pass (LP) NGD canonical TF and the characterization approach is established. It is shown in which condition the first order difference equation represents a LP-NGD circuit. Then, the design method of typical LP-NGD predictor as numerical circuit is introduced in function of the expected time-advance. The NGD predictor time-variation property is theoretically initiated. The NGD time-advance varied from -7 days to -1/2 days is investigated with deterministic data prediction processing from 5-months bi- exponential waveform data. The predicted data with time-advance of about -4 days was confirmed by analytical computation and simulation. The LP-NGD digital predictor feasibility is validated with monthly COVID-19 randomly arbitrary data by computed and virtually tested results. It was investigated with sensitivity analysis that the prediction performance is better when the input signal is smoothed enough. As expected, prediction result showing very good correlation with input data is demonstrated.

On the fractional domain analysis of negative group delay circuits

SummaryIn this work, the analysis of negative group delay circuits in fractional domain has been conducted. The low pass and the high pass negative group delay circuits constructed based on passive network have been chosen as our candidate circuits. For performing the analysis in fractional domain, the novel Caputo–Fabrizio derivative‐based fractional impedance have been introduced to both circuits. The crucial parameters, the necessary conditions, and the existence conditions of both candidate negative group delay circuits have been formulated. The simulations have been conducted based on the formulated results where the comparisons with the conventional prototypes have been made. The verifications by the proof‐of‐concept circuits have also been performed. In addition, the effects of variation in the order of fractional impedances have been investigated. In summary, it has been found that considering these negative group delay circuits in the fractional domain, which effectively taking unavoidable nonidealities that cannot be modeled in conventional domain into account, significantly alters their characteristics especially the low pass circuit. However they can retain their low pass and high pass negative group delay functions.

Design of a quint-band passive NGDC by using Taguchi’s optimization method

This article presents a quint-band passive negative group delay circuit (Q-NGDC) by using Taguchi’s optimization method for the first time. This Q-NGDC mainly consists of a semi-circle and a multi-stub resonator, and it is evolved from a simple NGDC (Type I) to a well-designed one (Type VI) through three optimization stages. It is found that, with the application of Taguchi’s method (TM) in conjunction with full-wave simulations, the efficiency of the designed passive multi-band NGDC has been improved significantly. The proposed Q-NGDC was fabricated and tested, and the experimental results show that the five operation bands have been achieved at the center frequencies of 1.76, 2.80, 3.84, 4.42, and 5.28 GHz, with the corresponding group delay values of −1.85, −2.15, −1.45, −1.6, and −1.1 ns. The measured transmission coefficients are −4.4, −7.8, −9.7, −9.3, and − 8.9 dB. Furthermore, the proposed NGDC shows the best figure of merit (FOM) at each resonant frequency with a relatively small size. The proposed NGDC can be potentially applied to WCDMA, 5G communication, Zigbee (IEEE802.15.4), and Wi-Fi (IEEE802.11n) systems.

Low-Pass NGD Digital Circuit Application for Real-Time Greenhouse Temperature Prediction

An original application of low-pass (LP) negative group delay (NGD) digital circuit for real-time prediction of greenhouse temperature is investigated. Synthesis formulas allowing to determine the LP-NGD parameters in function of the targeted time-advance are established. The characterization technique of LP-NGD digital circuit implemented on microcontroller platform is validated with a deterministic analytical and real temperature slow pulse signals presenting several hour time-duration. The real-time temperature prediction is tested by employing a commercial temperature sensor in the greenhouse environment. As expected, very good prediction of greenhouse temperature is observed. The experimental result demonstrates an outstanding prediction of ambient temperature variation with -30 minutes time-advance during more than fifty-hour or more than two-day real-time sensing. The present research result opens an innovative roadmap for the future smart buildings and industries where the temperature control and monitoring are particularly key challenging tasks.

All-Pass NGD FIR Original Study for Sensor Failure Detection Application

This paper deals with original design, implementation, test, and potential application of finite impulse response (FIR) with uncommon all-pass negative group delay (AP-NGD) circuit. The counterintuitive AP-NGD numerical circuit theory is established. Design method of first order AP-NGD circuit is introduced with respect to the specified time-advance. The first order difference equation was synthesized, designed, and implemented in STM32 Microcontroller Unit, and experimented to validate the AP-NGD characteristics. The AP-NGD FIR prototype was tested in the time-domain with Gaussian and arbitrary waveform sensored signals. Calculated and experimented results in very good agreement with the most significant time-advance -10 s ever experimented before are obtained. The potential industrial application of the NGD predictor for sensor fault diagnosis in real-time is described.

A Compact Negative Group Delay Microstrip Diplexer with Low Losses for 5G Applications

Microstrip Diplexers play an important role in modern wireless communication systems. In this paper, a novel compact microstrip diplexer based on spiral cells is presented. The proposed resonator primarily consists of two spiral thin lines connected to a pair of coupled lines. This novel resonator is analyzed mathematically to find its behavior and tune the dimensions of the final layout easily. Using the analyzed resonator, two bandpass filters (BPFs) are designed. Then, a novel high-performance microstrip diplexer is obtained by designing and integrating these two BPFs. The center frequencies of the first and second channels of the proposed diplexer are 1.86 GHz and 4.62 GHz, respectively. The proposed diplexer boasts a remarkably small size of 0.004 λg2 and features flat channels with low insertion losses of only 0.048 dB and 0.065 dB for the first and second channels, respectively. The maximum group delays of S21 and S31 are 0.31 ns, 0.86 ns, respectively, which are good values for a modern communication system. Meanwhile, inside its passbands for some frequency ranges, its group delays are negative. Thus, using this diplexer can decrease the signal dispersion. The 1st and 2nd passbands are wide with 47.3% and 47.1% fractional bandwidths (FBW), respectively. Therefore, this diplexer can be easily and successfully used in designing high-performance RF communication systems.

Tailoring octave-spanning ultrashort laser pulses using multiple prisms.

We demonstrate a novel pulse shaper in which an incident laser beam is angularly dispersed by a first prism, and then it is split into separate beams using multiple prisms. Since this new pulse shaper offers independent control of the amplitude and phase of the separate beams, it can produce pulses having desired temporal shapes. Furthermore, it imposes a significant amount of negative group delay dispersion (GDD) over an octave spectrum near visible, which can compensate for a positive GDD accumulated in the process of spectral broadening. Consequently, single-cycle or few-cycle laser pulses can be produced without the need for chirped mirrors.

Compact and Wideband Flat Negative Group Delay Circuit Investigation

This paper introduces a dual transmission structure with bandpass (BP) negative group delay (NGD) wideband flat behavior. The flat BP-NGD topology is analytically modelled from equivalent circuit composed of transmission line (TL) and stepped-impedance resonator connected by two resistors. As proof of concept (POC), by tuning TL characteristic impedances, the influences of circuit physical variables on NGD flatness are illustrated by parametric study. The flat BP-NGD POC circuit with a size of 48.2 mm×90.8 mm (0.2λg 0.38λg) is designed, fabricated, and measured. A very good agreement is confirmed by simulation and experimentation results of 680 MHz over 290 MHz (42.6%) NGD bandwidth (BW) around 0.7 GHz NGD center frequency. Also, the flat BP-NGD BW reaches 223 MHz (31.8%) over 569 MHz to 792 MHz with ±0.05 ns group-delay fluctuation with insertion and reflection losses better than 14 dB.

Group delay compensation based on negative group velocity effect of spoof surface plasmon polaritons

Negative group velocity (NGV) exists only in the anomalous dispersion band with resonance absorption. In this paper, it is verified that spoof surface plasmon polaritons (SSPPs) with spiral-shaped periodic units have the NGV characteristics near cutoff frequency. The negative group delay of this NGV SSPP can be used to achieve the compression of the pulse signal, and also to compensate the positive group delay with high efficiency. Of course, this group delay compensation scheme based on NGV may introduce an absorption loss, which is the characteristic of all passive negative group delay circuits.

Design theory of compact power divider with reconfigurable power division and negative group delay characteristics

This article presents the combined analysis of reconfigurable power division and negative group delay (NGD) in a power divider. A novel composite transmission line based reconfigurable power divider with high power division ratio, variable negative group delay, and lower characteristic impedance is presented in this work. The impedance transformation in composite transmission lines control both negative group delay and power division. This power divider possesses a wide range of power division ratios from 1 to 39, adequate isolation, impedance matching, and NGD of -3.4 ns to -4.7 ns in the reconfigurable transmission path. The negative group delay is achieved without using any additional group delay circuits. Theoretical equations corresponding to the low characteristic impedance of the transmission line sections and that of isolation elements are derived. The measurement results justify the attainment of high tuning of the power division ratio and negative group delay. Isolation and return loss are higher than − 15 dB at the centre frequency of 1.5 GHz. The significant contributions of this design can be listed as the wide reconfigurable power division along with negative group delay and reduced size.

Negative group-delay assisted anomalous propagation in stacked Split Ring Resonator array

This paper explores a novel method to achieve negative group delay-assisted anomalous propagation without significant signal attenuation using stacked Split-Ring Resonator (SRR) array in the microwave regime. A sub-wavelength stacking thickness between the SRR layers creates transverse magnetic dipole moments due to the excitation of anti-parallel currents on these layers resulting in increased transmission amplitude. Multipole scattering theory has been utilized to extract the reason behind anomalous propagation by evaluating the scattered power from the principal electric and magnetic dipole moments excited on the structure. Time-domain analysis are performed on the samples, and negative group delay behavior is confirmed by observing the precedence of the output electromagnetic Gaussian pulse within the anomalous dispersion regime. The coupling effects are studied numerically using full-wave solvers and verified in experiments by performing transmission measurements inside an anechoic chamber.

A negative group delay rectangular waveguide based on corrugated tantalum nitride slow wave structure

AbstractIn this letter, a rectangular waveguide with controlled negative group delay (NGD) is proposed. The equivalent circuit of the structure is proposed and analyzed. The NGD value and NGD center frequency can be adjusted continuously by the corrugation width and height. Simulation results showed that NGD values of up to −0.7 ns were achievable. The fractional bandwidth was up to 5.67%, at which point the NGD response was observed. A prototype of the proposed structure was fabricated and characterized. Results showed that the fabricated structure was capable of generating a group delay of up to −0.09 ns at 18.9–20 GHz, which was consistent with theoretical and simulated predictions. To the best of our knowledge, this is the first time negative group delay has been achieved in the microwave‐band in a rectangular waveguide.

Frequency-Selective Surface Based on Negative-Group-Delay Bismuth–Mica Medium

Negative group delay may be observed in dispersive media with anomalous dispersion in a certain frequency range. The fact that an outgoing wave packet precedes an incoming one does not violate the causality principle but is only a consequence of a waveform reshaping. This effect is observed in media such as photonic crystals, hyperbolic and epsilon-near-zero metamaterials, undersized waveguides, subwavelength apertures, side-by-side prisms, and resonant circuits at various frequencies. The current work is devoted to the design of a simple negative-group-delay medium with tunable properties in the THz frequency range. This medium consists of a bismuth-based frequency-selective surface on a dielectric substrate and may be tuned both statically and dynamically. While a geometry variation defines a main form of an effective permittivity dispersion and group delay/group velocity spectra, an external voltage allows one to adjust them with high precision. For the configuration proposed in this work, all frequency regions with noticeable change in group delay/group velocity lie within atmospheric transparency windows, which are to be used in 6G communications. This medium may be applied to THz photonics for a tunable phase-shift compensation, dispersion management in systems of THz signal modulation, and for encoding in next-generation wireless communication systems.

Construction of a Mirror-Dispersion-Controlled Kerr Lens Mode-Locked Ti:Sapphire Pulse Laser Oscillator

We have successfully constructed a Kerr lens mode-locked (KLM) Ti:sapphire oscillator to generate ultrashort pulses of ~18 fs. The oscillator consists of only 5 elements including a pair of double-chirped mirrors to balance negative group delay dispersion in the cavity. The bandwidth of the mode-locked laser oscillator spectrum is from 600 nm to 950 nm and pulse energy is 1.5 nJ. Both the output spectrum and the output power were stable against environmental disturbance. For the pulse characterization, a second harmonic generation frequency resolved optical gating method was used.

Slow and Fast Light in Microwave Interferometers

We propose and demonstrate a method for manipulation of group velocity from slow-to-fast light (SFL) in a two-beam Mach–Zehnder interferometer in radio frequency (RF) regime. The subluminal, superluminal, and tunneling propagation regimes occur in a narrow frequency band around the resonance frequency of the interferometer where destructive interference occurs. Importantly, the group velocity at the resonance frequency can be controlled by simply adjusting the transmission magnitude of the signals from the two beams, without changing the length of the interferometer. Models that fully describe the SFL effects in the microwave interferometer system are developed and closed-form expressions for the prediction of group delays at the resonance frequency are obtained. The simple and effective method is verified through numerical calculations and experimental measurements. We also demonstrate that the proposed method applies to a microwave cavity interferometer. A proof-of-concept experiment is performed using a custom open-ended coaxial cable resonator (OE-CCR). Positive and negative group delays are experimentally measured when the resonator is set at different coupling states.

T-Topology Coupler-Based Bandpass Negative Group Delay Active Circuit Design and Test

This article develops a design method for the bandpass negative group delay active microwave circuits. The theoretical calculations, simulation results, and measurements on a tested prototype show excellent consistency. —Haralampos Stratigopoulos, Sorbonne Université, CNRS, LIP6