Low Group Delay Research Articles

Wideband Air‐Filled Coaxial Filter Line

ABSTRACTA design for manufacturing (DFM) of a well‐performing wideband coaxial filter line using direct metal laser sintering (DMLS) additive manufacturing is proposed. The demonstrated transmission line is an air‐filled coaxial line chosen for low loss and consistent group delay over the bandwidth. Transmission line theory is used first to account for the impact of the shorted stub needed to support the central conductor. Deviations due to parasitics are described to transition the design from an ideal model to a physical prototype. The constraints inherent in DMLS are discussed and accounted for throughout the DFM. This process is demonstrated with a prototype having return and insertion losses of greater than 10 dB and less than 1.64 dB, respectively, over a 5.3:1 bandwidth from 6.4 to 33.9 GHz with a flat group delay of 129 ps ± 7%.

An Ultra-Compact Microstrip Bandpass Filtering Coupler with Suppressed Harmonics and Low Group Delay: A Novel Structure for 5G Applications

An Ultra-Compact Microstrip Bandpass Filtering Coupler with Suppressed Harmonics and Low Group Delay: A Novel Structure for 5G Applications

Enhancing phase modulation and group delay in reflective Huygens metasurfaces via a Fabry-Perot cavity

Huygens metasurfaces exhibit excellent optical properties such as 2π phase modulation and slow light effects. However, they face challenges including wide bandwidth and low group delay due to their high radiation losses. Here, we propose a reflective Huygens metasurface coupled with an F-P cavity. We demonstrate that F-P resonance modes can couple with magnetic-quasi-bound-state (M-QBIC) and electric-quasi-bound-state (E-QBIC) in the Huygens metasurface through constructive interference, significantly enhancing the quality factors of both QBICs. Through structural parameter optimization, our reflective Huygens metasurface achieves 4π phase modulation and a high group delay of up to 166 ps. Compared to the non-coupled Huygens metasurface with the same structural asymmetry, the group delay of the F-P coupled reflective Huygens metasurface is enhanced by up to 30 times. Our design reduces the fabrication precision requirements for Huygens metasurfaces, enabling similar group delays to be achieved in low-symmetry coupling structures as in highly symmetric non-coupling structures. Additionally, the performance of this metasurface shows robustness to changes in incident light polarization. This design highlights the potential for achieving high-quality factors, large phase modulation, and large group delay, offering new avenues for the design of highly sensitive tunable devices, efficient nonlinear optical devices, and narrowband slow light devices.

A Metamaterial Bandpass Filter with End-Fire Coaxial Coupling

A miniaturized metamaterial (MTM) bandpass filter (BPF) based on end-fire coaxial coupling is proposed. End-fire coaxial coupling is achieved by using the coaxial cavity to connect with the SubMiniature version A connector. The subwavelength characteristics of the MTM lead to the miniaturization advantages of the filter in transverse dimensions. Moreover, the longitudinal length of the coaxial cavity can be sharply reduced by introducing matched blocks. As a result, the proposed filter has miniaturization merit both in transverse and longitudinal dimensions. The full-wave simulation results further reveal that the MTM BPF exhibits the advantages of low loss, low reflection, and low group delay. Additionally, the fractional bandwidth is approximately 13% when |S11| is less than −15 dB. The MTM BPF might have potential applications to array antennas for easily being expanded to two dimensional arrays.

Design and preparation of L-band multilayer low-group delay filter based on inner sputtering

Article propose a design for an L-band multi-layer MEMS cross-finger filter based on pore interior wall sputtering. Article analyze the structural parameters, such as resonator thickness and TSV structure, using HFSS simulation software. Findings indicate that the filter has a central frequency of 1.5 GHz, a bandwidth of 140 MHz, a band loss of less than 1 dB, return loss is greater than 25 dB, and a band group delay of less than 800 ps. Furthermore, Article conduct process design optimization and finished product testing for the filter, including optimizing the TSV process for the hole inner wall sputtering process. These results demonstrate the filter's broad application prospects.

Design and fabrication of a microstrip triplexer with wide flat channels for multi-band 5G applications.

In this paper, a new microstrip triplexer is designed to work at 2.5 GHz, 4.4 GHz and 6 GHz for mid-band 5G applications. All channels are flat with three low group delays (GDs) of 0.84 ns, 0.75 ns and 0.49 ns, respectively. Compared to the previously reported works, the proposed triplexer has the minimum group delay. The designed triplexer has 18.2%, 13.7%, 23.6% fractional bandwidths (FBW%) at 2.5 GHz, 4.4 GHz and 6 GHz, respectively. The obtained insertion losses (ILs) are low at all channels. These features are obtained without a noticeable increase in the overall size. A novel and simple resonator is used to design the proposed triplexer, which includes two pairs of coupled lines combined with a shunt stub. A perfect mathematical analysis is performed to find the resonator behavior and the layout optimization. The type of shunt stub is determined mathematically. Also, the smallness or largeness of some important physical dimensions is determined using the proposed mathematical analysis. Finally, the designed triplexer is fabricated and measured, where the measurement results verify the simulations.

Ultra-wideband high gain low group delay variation amplifier for phased-array radar system

This paper describes a ultra-wideband (UWB) three-stage cascaded high gain amplifier with low group delay variation for phased-array radar system. The shunt inductor at the input not only provides an electrostatic discharge (ESD) path to ground, but also introduces a new notch for S11, thus extending the matching bandwidth. Staggered tuning of load impedance peaks at each stage facilitates a balance between flat gain and low group delay variation. The output stage further enhances the overall gain while reinforcing bandwidth and stability through resistive feedback, and employs an adaptive bias circuit for linearity improvement. Implemented in SMIC 40-nm CMOS technology, the proposed amplifier achieves good input impedance matching, flat gain and low group delay variation of ±73.5 ps over 4.7–16 GHz. The whole power consumption is 198.3 mW and the output 1 dB compression point (OP1dB) is greater than 9 dBm. After careful design, the chip size is 0.64 mm2.

Design Study High Reflectors Graded Index Mirror Dispersive Properties

This paper investigates the dispersive properties of a spectral filter—a quarter-wave (QW) mirror. The study considers the modeling with a smoothly changing refractive index of the applied material (Rugate filter) using Fourier transform analysis of a high and low refractive index. These chirped structures exhibit high reflectivity and low group delay dispersion. The introduced result in this study is in some way better than already existing ones and/or can be used to obtain a meaningful practical effect, because it adopts calculation methods that are characterized by the accuracy and reliability of data using different statistical parameters and can be adopted with all modern and old methods of preparation. These improvements can have significant implications for various applications. Moreover, we investigate different statistical parameters, such as mean, median, mode, and standard deviation (STD), and analyze their impact on the rugate filter group delay (GD) and group delay dispersion (GDD) performance.

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.

Power-efficient polarization-insensitive tunable microring filter on a multi-layer Si3N4-on-SOI platform.

We develop and demonstrate a non-duplicate polarization-diversity tunable bandpass optical filter by leveraging the bi-directional transmission of add-drop dual-coupled microring resonators (MRRs) on a multi-layer Si3N4-on-silicon-on-insulator (SOI) platform. By using Euler-bends, we implement compact and low-loss Si3N4 MRRs with an equivalent bending radius of ∼38 µm. Fiber-to-fiber (on-chip) insertion loss of 4.3 dB (1.7 dB) with a low polarization-dependent loss of <0.5 dB and low differential group delay of <2.5 ps is achieved. The extinction ratio is more than 30 dB. The thermo-optic tuning efficiency of the Si3N4 MRRs is improved with a suspended micro-heater design. As a result, a wavelength tuning range of ∼2 nm and a 3-dB bandwidth tuning range of 20 GHz are experimentally demonstrated. The tuning efficiency is 33 pm/mW, which is ∼7.5 times higher than the previous design. This reconfigurable polarization-insensitive filter, with low loss, low cross talk, and high power efficiency, is highly promising for practical applications in optical communication and signal processing.

Minimized Group Delay FIR Low Pass Filter Design Using Modified Differential Search Algorithm

Designing a finite impulse response (FIR) filter with minimal group delay has proven to be a difficult task. Many research studies have focused on reducing pass band and stop band ripples in FIR filter design, often overlooking the optimization of group delay. While some works have considered group delay reduction, their approaches were not optimal. Consequently, the achievement of an optimal design for a filter with a low group delay value still remains a challenge. In this work, a modified differential search optimization algorithm has been used for the purpose of designing a minimal group delay FIR filter. The results obtained have been compared with the classical techniques and they turned out to be promising.

A Nonlinear Optimization Design Algorithm for Nearly Linear-Phase 2D IIR Digital Filters

In this paper, a new optimization method for the design of nearly linear-phase two-dimensional infinite impulse (2D IIR) digital filters with a separable denominator is proposed. A design framework for 2D IIR digital filters is formulated as a nonlinear constrained optimization problem where the group delay deviation in the passband is minimized under prescribed soft magnitude constraints and hard stability requirements. To achieve this goal, sub-level sets of the group delay deviations are utilized to generate a sequence of filters, from which the one with the best performance is selected. The quality of the obtained filter is evaluated using three quality factors, namely, the passband magnitude quality factor Qh and the group delay deviation quality factor Qτ, while the third one is a new quality factor Qs that assesses the performance in the stopband relative to the minimum filter gain in the passband. The proposed framework is implemented using the interior-point (IP) method in a MATLAB environment, and the experimental results show that filters designed using the proposed method have good magnitude response and low group delay deviation. The performance of the resulting filters is compared with the results of other methods.

Microstrip lowpass-bandpass triplexer with flat channels and low insertion losses: Design and fabrication for multi-service wireless communication systems

In this work, a new basic microstrip structure is proposed and analyzed to obtain a lowpass-bandpass triplexer without any extra matching networks. This is despite the fact that the number of literature on lowpass-bandpass triplexers that have been introduced so far is very low. The lowpass channel cut-off frequency is tuned at 1.85 GHz which makes it appropriate for mid-band 5G and GSM applications. The bandpass channels work at 3.25 GHz and 6.65 GHz for S-band, 5G, WiMAX and C-band applications. The designed triplexer occupies a compact area of 0.021 λg2. In comparison with the previously reported triplexers, the presented triplexer has three low insertion losses of 0.54 dB, 0.16 dB and 0.55 dB. Also, all its channels are flat with three low group delays of 0.79 ns, 0.98 ns and 0.85 ns. For verifying the designing technique and simulation results, we fabricated and measured our triplexer, where all the obtained results are close to each other.

32-channel wide-bandwidth massive RF photonic combiner based on distributed groups of arrayed photodetectors.

We propose and experimentally demonstrate a low-loss, radio frequency (RF) photonic signal combiner with flat response from 1 GHz to 15 GHz and low group delay variation of 9 ps. The distributed group array photodetector combiner (GAPC) is implemented in a scalable Si photonics platform and has applications in RF photonic systems that rely on combining massive numbers of photonic signals.

Design of elliptical photonic crystal fiber (E-PCF) for the transmission of 116 OAM channels across the S, C, L and U bands

Orbital angular momentum (OAM) modes over photonic crystal fibers (PCFs) have shown great capability in unleashing the available data rates in optical communication systems. In this paper, we propose and numerically design a novel elliptical photonic crystal fiber (E-PCF) using assisted Germania-doped silica as a material background and elliptical air holes. Using a systematic scanning methodology, we adjusted the E-PCF key parameters with the aim to explore appropriate designs that support large number of OAM channels featuring low confinement loss (CL). Numerical simulations using finite element method (FEM) show the supports of large number of independent/separate OAM channels (116 OAM with Δneff≥ 10−4). A detailed numerical modal analysis has been carried out over the S + C + L + U communication bands show that the designed E-PCF handles robust OAM modes. This includes low chromatic dispersion (CD = 92 ps/km/nm), low differential group delay (<60 ps/km), high effective mode area (max Aeff = 124 µm2), low nonlinearity coefficient (γ < 2.6 /W/m) and low confinement loss (Max CL = 2.07 × 10−4 dB/m). The obtained results and the comparisons with those recently reported in literature shows that the designed E-PCF could find applications in next-generation optical communication systems that uses OAM modes as data carriers.

A High-Efficiency Diplexer for Sustainable 5G-Enabled IoT in Metaverse Transportation System and Smart Grids

Symmetry is essential in the design of complex systems like the Metaverse Transportation Sys-tem (MTS) and helps ensure that all components work together effectively. In the development of a microstrip diplexer for 5G-enabled IoT and MTS, maintaining symmetry is crucial to achieving flat responses with low group delays. By integrating transportation technology and the Metaverse, the Metaverse Transportation System (MTS) can greatly improve the effectiveness and intellect of transportation systems in reality. To establish a dependable network, it is essential to include 5G-enabled Internet of Things (IoT) and sensor networks with a sustainable design that focuses on efficiency and energy conservation. A three-channel microstrip lowpass-bandpass diplexer has been developed for 5G-enabled IoT and MTS implementation. Multi-channel designs are rare due to the complex design process, but this diplexer is very compact at only 0.004 λg2. All channels have flat responses with group delays of 0.34 ns, 1.7 ns, and 0.34 ns at the lower, middle, and upper passbands, respectively. The lowpass channel has a cut-off frequency of 1.22 GHz, suitable for mid-band 5G applications. Compared to previous work, this diplexer achieves the smallest size, lowest group delay, and insertion and return losses at the lower channel. It consists of a lowpass-bandpass section connected to a band-pass filter analyzed mathematically, and its performance has been verified through simulation and measurement with good accuracy.

Heterogeneously Integrated Multicore Fibers for Smart Oilfield Applications

In the context of Industry 4.0, the smart oilfield is introduced, which relies on large-scale information exchange among various parts, and there is an urgent need for special fiber links for both increased data transmission capacity and high-sensitivity distributed sensing. Multicore fibers can be expected to play a critical role, in the parts of cores that are responsible for data transmission, while others are used for sensing. In this paper, we propose a heterogeneously integrated seven-core fiber for interconnection and awareness applications in smart oilfields, which could not only support digital and analog signal transmission but could also measure temperature and vibration. The core for digital signal transmission has a low differential mode group delay of 10 ps/km over the C-band, and the crosstalk between adjacent cores is lower than −55 dB/km at the pitch of 50 μm. A 25-Gbaud transmission over 50 km is simulated. Each core for analog signal transmission has a large effective area of 172 μm2 to suppress the nonlinear effect due to the watt-scale input power. The proposed heterogeneously multicore fiber exhibits great potential to be applied in smart oilfields, meeting the demand for efficient and cost-effective oil production.

Design and Analysis of Z-Trench-Assisted 9-LP-Mode Fiber With Low Differential Modal Group Delay and High Spatial Density

Design and Analysis of Z-Trench-Assisted 9-LP-Mode Fiber With Low Differential Modal Group Delay and High Spatial Density

Implementation of broadband optical receiver amplifier with low group delay variation

Considering the ever-increasing growth of data traffic in communication systems, optical receiver amplifiers are now emerging as a key feature of various optical receivers. This article presents a broadband optical receiver amplifier for high-speed and low latency communication systems. The proposed amplifier is based on the distributed amplifier configuration, and employs the negative group delay technique to reduce the group delay variation. The experimental results of the proposed amplifier show a 15 dB average gain, 3 dB noise figure, and 8 ps group delay variation at frequency ranging from DC to 40 GHz. To the best of our knowledge, the proposed distributed amplifier (DA) demonstrates the lowest group delay variation among the reported forward optical module distributed amplifiers (DAs) for high data rates applications.

Dynamic terahertz transmission based on coupling reconfiguration of spoof surface plasmon polaritons.

In this paper, we propose a dynamic transmission structure based on the coupling reconfiguration of spoof surface plasmon polaritons (SSPPs) in a 2D coplanar grating. By embedding a VO2 film into the signal line, the dynamic transmission is realized by reconfiguring the coupling of terahertz waves from quasi-TEM waves to SSPPs. The analysis shows that the transmission can be modulated in almost the entire band of the SSPPs, which further benefits a promising group delay due to the weak dispersion characteristic in the frequency region much lower than the cut-off frequency of SSPPs. In addition, for the dynamic modulation caused by the coupling reconfiguration, only rather a small area of VO2 film is needed to break the robustness of the 2D coplanar grating. Therefore, the coupling reconfiguration mechanism proposed in this paper facilitates the realization of an easily on-chip integrated dynamic SSPPs transmission structure with ultra-large bandwidth, and low group delay time difference. Accordingly, the presented mechanism will play a positive role in promoting the development of terahertz dynamic devices.