Low Group Delay Research Articles

Minimax Design of M-D Sparse FIR Filters With Arbitrary Frequency Response Using SOCP

The number of coefficients of multi-dimensional (M-D) finite-extent impulse response (FIR) filters increases exponentially with the number of dimensions leading to significantly high computational complexities. In this brief, we propose a minimax design method for M-D FIR filters having sparse coefficients, therefore, having low computational complexities. We consider the design of M-D FIR filters with arbitrary frequency responses and low group delays of which the coefficients are complex valued. We formulate the minimax design as a second-order cone programming problem. Design examples confirm that M-D sparse FIR filters designed using the proposed method provide more than 60% reduction in the computational complexity for a similar error in the frequency response approximation compared to M-D FIR nonsparse filters designed using previously proposed minimax methods.

Compact high isolation UWB MIMO antennas

In this work, two elements (with two versions) compat UWB MIMO antennas are designed and fabaricted. CST software is used in the simulation process. The two elements MIMO antenna have a size of 29.5 × 60 mm2. Measured S parameters show that the MIMO antennas work well from 3 GHz up to 20 GHz (representing the maximum working frequency of the measurent instrumnts). Mesurement results show that the isolation between the antenna elemnts is higher than 23 dB for the first version of the two elements UWB MIMO antenna. In addition, mesurement results show that the isolation between the antenna elemnts is higher than 30 dB for the second version of the two elements UWB MIMO antenna. Measurements show a channel capacity loss lower than 0.4 bps/Hz and a low group delay variation.

Analysis and optimization of few-mode fibers with low differential mode group delay by variational method

Mode-division multiplexing (MDM) technology based on few-mode fibers (FMFs) is the current research hotspot of optical fiber communication system because of its ability to increase the transmission capacity several times. When the number of multiplexed modes is large, the crosstalk between modes can be removed by multiple input multiple output digital signal processing algorithm at the receiving end. The larger the differential mode group delay (DMGD, <inline-formula><tex-math id="Z-20220504070336-1">\begin{document}$ \tau_{\rm DMGD} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20212198_Z-20220504070336-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20212198_Z-20220504070336-1.png"/></alternatives></inline-formula>), the more complex the algorithm is. Therefore, in order to reduce the complexity of the receiver, it is necessary to use FMFs with low DMGD. The variational method is proposed to analyze any FMFs with higher refractive index of core than that of cladding. The analytical formula of the fundamental mode size, the normalized propagation constant for each of all guided modes, and DMGD relative to the fundamental mode are derived. Moreover, their relationship with the normalized frequency and other fiber manufacturing parameters are given. On this basis, the graded-index FMFs are studied, and the fiber parameters are optimized. The optimization parameters are the difference between the maximum core refractive index and cladding refractive index <i>n</i><sub>1</sub> – <i>n</i><sub>2</sub> = 0.01, the core radius <i>a </i>= 14 μm, and the paramenter of refractive index distribution <i>α </i>= 1.975. In the optimized FMF, 6 LP modes can be guided and |<inline-formula><tex-math id="Z-20220504070445-1">\begin{document}$ \tau_{\rm DMGD} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20212198_Z-20220504070445-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20212198_Z-20220504070445-1.png"/></alternatives></inline-formula>| is less than 15 ps/km within the C band and L band. In the end, the effects of the fiber manufacturing errors on DMGD are discussed.

A New ANFIS-Based Hybrid Method in the Design and Fabrication of a High-Performance Novel Microstrip Diplexer for Wireless Applications

In this work, we have used a novel adaptive neuro-fuzzy inference system (ANFIS) method to design and fabricate a high-performance microstrip diplexer. For developing the proposed ANFIS model, the hybrid learning method consisting of least square estimation and back-propagation (BP) techniques is utilized. To achieve a compact diplexer, a designing process written in MATLAB 7.4 software is introduced based on the proposed ANFIS model. The basic microstrip resonator used in this study is mathematically analyzed. The designed microstrip diplexer operates at 2.2[Formula: see text]GHz and 5.1[Formula: see text]GHz for wideband wireless applications. Compared to the previous works, it has the minimum insertion losses and the smallest area of 0.007 [Formula: see text] (72.2[Formula: see text]mm2). It has flat channels with very low group delays (GDs) and wide fractional bandwidths (FBWs). The GDs at its lower and upper channels are only 0.48[Formula: see text]ns and 0.76[Formula: see text]ns, respectively. Another advantage of this work is its suppressed harmonics up to 12.9[Formula: see text]GHz (5th harmonic). To design the proposed diplexer, an LC model of the presented resonator is introduced and analyzed. To verify the simulation results and the presented ANFIS method, we fabricated and measured the proposed diplexer. The results show that both simulations and measurements data are in good agreement, which give reliability to the proposed ANFIS method.

Low loss negative group delay circuit using self‐packaged suspended line

A matched negative group delay (NGD) circuit with ultra-low insertion loss by using self-packaged multi-layer suspended line is proposed. Two transmission paths with different electric-lengths are used to produce positive phase slope, which would bring a negative group delay, while a coupled line is used for matching, and the commonly applied absorption resistors are not required. The NGD circuit has been fabricated and measured, and the design has been demonstrated with a measured NGD time of −2.84 ns, a NGD bandwidth of 34 MHz, a low insertion loss/signal attenuation (S21) of no more than 2.73 dB, and a S11 attenuation of about 27.8 dB. Both self-packaging and metallized air cavities are used to reduce the wave leakage, and the multiple via holes usually used for electromagnetic shielding are saved, which greatly reduce the fabrication complexity.

АНАЛИЗ УПРАВЛЯЕМОСТИ НЕКОТОРЫХ ЦИФРОВЫХ ФИЛЬТРОВ С КОНЕЧНОЙ ИМПУЛЬСНОЙ ХАРАКТЕРИСТИКОЙ

This overview article covers finite impulse response filters and filter banks. The use of these filtersfor hearing aids is considered. Ways to compensate for hearing loss and ways to increase loudnessusing broadband amplification are considered. A schematic diagram of a method for digitalsignal processing using a bank of filters, as well as a technique for synthesizing interpolation filterswith low computational complexity, is presented. Also, the application of the MATLAB system for thesynthesis of narrow-band non-recursive FIR filters, their design procedure, methodology and examplesare considered. Finite Impulse Response (FIR) filters and filter banks have specific propertiesthat guarantee stability. Therefore, they are popular in many applications such as communicationsystems, audio signal processing, biomedical instruments, and so on. Unfortunately, due to the longerwavelength, the cost of implementing an FIR filter is usually not higher than an infinite impulse response(IIR) filter that meets the same requirements. It is well known that the length of an FIR filter isinversely proportional to its transition bandwidth. Therefore, the disadvantage becomes acute when agiven filter has a narrow transition band. The main goal is to consider computationally efficientmethods for designing FIR filters and filter banks. The masking method (FRM) results in significantsavings in the number of multipliers. Next, a 16-band, low group delay, non-equal-spacing digitalFIR filter bank is considered. Overall latency is significantly reduced as a result of a new filter structurethat reduces the interpolation factor for prototype filters. Masking filter may be an interpolatedfinite impulse response (IFIR) filter that helps reduce complexity.

Design and Fabrication of a Novel Ultra Compact Microstrip Diplexer Using Interdigital and Spiral Cells

A dual-band bandpass-bandpass microstrip diplexer with very small size and good performance is designed in this work. The proposed diplexer has a novel structure which is introduced for the first time in this paper. In comparison with the previously reported diplexers, it occupies the most compact size of 0.002 λg2 (226.7 mm2), fabricated on 0.787 mm dielectric substrate height. The resonance frequencies of the presented diplexer are located at 0.76 GHz and 1.79 GHz making it suitable for the global system for mobile communications (GSM) applications. It has a wide flat channels with two fractional bandwidths (FBWs) of 41.1% and 50%. Another feature of the proposed diplexer is its ability to suppress the harmonics. It can attenuate the 1st to 7th harmonics. Moreover, it has low insertion losses and low group delays at both channels while the isolation and return losses are acceptable. Finally, the proposed diplexer is fabricated and measured to verify the simulation results, where a good agreement between the simulation and measurement results is obtained.

Substrate-Suspended Air Cavity Resonator and Its Application in Low Phase Noise Oscillator

In this paper, we present a substrate-suspended air cavity resonator featuring high-Q, consisting of five separate layers for confining electromagnetic energy. Its field distribution is analyzed in depth. By appropriately coupling the two resonators, a second-order Chebyshev bandpass frequency selection network is obtained, and design procedure is described. It forms a specific group delay response, in which high values can be achieved within a narrow frequency range around the center frequency. The frequency selection network has great flexibility in adjusting its magnitude and phase responses so that low insertion loss and high group delay are achieved simultaneously. This feature plays an important role in reducing phase noise when it is applied in a microwave oscillator. For demonstration, an X-band oscillator example was designed and fabricated. As the measured results show, it works at 11.16 GHz, and the phase noise at 100 KHz away from the oscillation frequency is as low as −120.68 dBc/Hz.

Short Broadband Fiber Gratings With Low Group Delay

Fiber Bragg gratings (FBGs) are essential optical components, which due to their design flexibility offer numerous prospects for a wide range of applications in fiber laser, sensor, and telecommunication technologies. Here we demonstrate that a phase mask interferometer driven by a deep-ultraviolet femtosecond laser enables inscription of FBGs with top-hat spectral reflection bandwidth. FBGs with the bandwidth of 2 nm have been achieved with inscription of several superimposed narrow FBGs with bandwidth less than 0.2 nm. The induced refractive index modulation profile of the superimposed gratings has been investigated with two measurement methods, namely, optical frequency domain reflectometry and the layer-peeling method. The analysis has shown that the spatial modulation index profile follows a sinc profile and has a very narrow central peak of less than 0.4 mm. Importantly, the FBGs provide low group delay values in comparison to their chirped counterparts. Additionally, the small center structure makes such gratings ideal for fiber sensing with high local resolution. The demonstrated FBG inscription method, developed initially to fabricate optical reflectors for infrared laser systems, can be translated to other applications, such as biophotonics, telecommunications, sensing and astrophysics.

Synthesis of Linear-Phase FIR Filters With a Complex Exponential Impulse Response

In this paper, a novel recursive realization method with word length reduced is proposed to synthesize linear-phase FIR filters for arbitrary bandwidth. By exploring the sparsity in the frequency domain, it constructs the desired impulse response with few complex exponential series (CES) and very sparse additional coefficients (AC) with equal length. The design problem is formulated as a combinatorial optimization problem by confining the frequencies of CES to a finite dictionary. To reduce the computational complexity at optimization, an iterative algorithm is presented, where appropriate frequencies of CES and zero locations of AC can be quickly determined. Thereafter, an efficient parallel structure is introduced to implement the proposed filter. To verify the performance of the proposed method, MATLAB simulation and Field-programmable gate array (FPGA) implementation are made. It shows that the proposed method requires 18bits23bits word length while the existing advanced recursive realization method the piecewise-polynomial-sinusoidal recursiveneeds 59bits59bits for the same filter specifications. Meanwhile, the method can achieve comparable multiplier reduction compared with the state-of-the-art low-complexity techniques but produce a low extra group delay. Moreover, it can realize variable bandedges with a fixed filter structure.

An Area-efficient Microstrip Diplexer with a Novel Structure and Low Group Delay for Microwave Wireless Applications

In this work, a novel structure of a microstrip diplexer consisting of coupled patch cells is presented. It works at 2.5 GHz and 4.7 GHz for wireless applications. The proposed structure is well miniaturized with a compact area of 0.015 λg2, fabricated on 0.787 mm substrate height. It has two wide fractional bandwidths (FBWs) of 28% and 17.9% at the lower and upper channels, respectively. Another feature of the proposed design is the low group delays, which are better than 0.4 ns for both channels. Moreover, the designed diplexer can suppress the harmonics up to 10 GHz. Meanwhile, the insertion losses at both channels are low. The design method is based on proposing an approximated equivalent LC circuit of a novel basic resonator. The information about the resonator behavior is extracted from the even and odd modes analysis of the proposed equivalent LC circuit. Finally, our introduced diplexer is fabricated and measured to verify the simulation results, where the simulated and measured results are in good agreement.

Design of Sparse FIR Filters with Low Group Delay

Design of Sparse FIR Filters with Low Group Delay

Designing High-Performance Multimode Fibers Using Refractive Index Optimization

The rich design landscape of optical fibers offers many opportunities for refractive index optimization. In particular, the refractive index profiles of multimode fibers (MMFs) and multicore fibers (MCFs) govern the behavior of spatial and polarization modes, including their bandwidth, mode count, mode coupling, modal dispersion, chromatic dispersion, and mode-dependent loss. In this article, we obtain update equations to optimize the shapes of fiber refractive index profiles for various applications using gradient descent. Starting with an initial fiber designed according to standard best practices, our methods iteratively modify the refractive index profile to improve upon the initial design. Interestingly, we see that optimization can sometimes yield large improvements in key fiber properties, such as a 20-fold reduction in the root-mean-square modal group delay spread, even though the index profile is changed very little from the initial design. We show that our methods can be used to tailor the mode coupling, modal dispersion and chromatic dispersion properties to desired values, and that optimization can be successfully applied over a large bandwidth. We provide illustrative design examples, including an optimization of a graded-index MMF with low group delay spread for long-haul mode-division-multiplexed transmission. Our algorithms can be used to design novel fibers or optimize existing fibers for next-generation transmission systems.

SICL‐based wideband crossover with low phase imbalance and group delay

This study presents a wideband crossover developed using substrate integrated coaxial line (SICL) technology. The proposed SICL-based crossover isolates the two physically overlapping channels by routing the signal in a middle conductor of SICL through the transmission line created in the top and bottom ground plane using a metalised blind via. An equivalent model is proposed to study the role of substrate height in the proposed crossover. The design methodology is affirmed by fabricating and testing the experimental prototype. The measured results show isolation between channels are more than 19 dB with better than 18 dB return loss and less than 1.2 dB insertion loss from 0.2 to 20 GHz. Owing to the non-dispersive nature of SICL line and simplistic design technique with minimal discontinuities the designed crossover demonstrates low peak-to-peak group delay variation, less than 0.04 ns over the entire bandwidth. The proposed crossover due to its symmetric design provides low path difference of less than $\pm $±2.45$^\circ $° up to 20 GHz ($\leq $≤$\pm 1^\circ $±1° up to 10 GHz) without any additional phase compensation technique. Utilization of electromagnetically robust self-packaged components designed in SICL technology provides superior front-end communication system within a small footprint.

UWB Fractal Antennas with Low Group Delay Variation

In this paper, two Sierpinski carpet UWB fractal antennas are designed and fabricated. The first fractal antenna is an antenna that has not any notch filter. The second one is an antenna with double notch filters. Antenna without notch filter has an operating band of (3.1–10.8) GHz with a gain of 5.3 dB at 10 GHz. This antenna has a low group delay variation. Antenna with double notch filters working at (3.36–12) GHz band shows a gain reduction and higher group delay at the filters operating band. Out of the notch filters operating band, the antenna has a low group delay variation and a gain near to the gain of the antenna without notch filters. The MIMO version of the antenna shows an operating band up to 10.8 GHz and isolation between ports higher than 15 dB.

High-Linearity 19-dB Power Amplifier for 140–220 GHz, Saturated at 15 dBm, in 130-nm SiGe

This letter presents an integrated power amplifier (PA), with high linearity and efficiency, which uses a passive four-way power distribution network to increase the maximum output levels. The gain unit consists of a differential preamplifier and power stage, interfaced by passive baluns at the input and output. The circuit is intended for ultrawideband mm-wave communication systems operating around 180 GHz. It exhibits a gain of 19 dB, with low ripple and group delay variation, over a large bandwidth of 80 GHz. The 1-dB compression point and the saturated output power occur around 13 and 15 dBm, respectively. The maximum dc power consumption is 830 mW and results in a power-added efficiency of up to 3.5%. The final chip occupies an area of 0.92 mm2 and is implemented in a 130-nm SiGe BiCMOS process, which offers a maximum oscillation frequency $f_{\text {max}}$ of 450 GHz. To the best of authors’ knowledge, this circuit demonstrates one of the largest bandwidths, in combination with the highest output power and best linearity, of any silicon-based PA operating above 200 GHz.

A Compact Ka-Band 4-bit Phase Shifter With Low Group Delay Deviation

This letter presents a compact $Ka$ -band 4-bit switch-type phase shifter with low group delay deviation (GDD) using 28-nm CMOS technology. A magnetically coupled all-pass network (APN) configuration is employed to achieve both equal and flat group delay characteristics versus frequency at each phase state. The measured rms phase error is 1.2°, and the gain error is 1.1 dB at 33 GHz. The average measured insertion loss is 12.8 dB at 33 GHz, and the input and output return losses are both lower than −10 dB from 29 to 37 GHz. The fabricated phase shifter has a compact size of 0.08 mm2 excluding pads, low GDD of ±4 ps, and rms group delay error of $Ka$ -band phase shifter has the lowest GDD per bandwidth (GDD/BW) compared with other reported passive phase shifters.

All-pass-based design of nearly-linear phase IIR low-pass differentiators

ABSTRACT A new approach to the design of the nearly linear phase infinite impulse response low-pass differentiators using a parallel all-pass structure is discussed in this paper. The magnitude and phase responses of the proposed low-pass differentiators are first formulated as functions of the phase responses of the corresponding all-pass filters, and a set of equations is derived such that the magnitude response approximates the ideal one in the weighted Chebyshev sense both in the passband and the stopband. The maximum passband phase response linearity error is shown to be related to the maximum passband magnitude error and the value of an additional design parameter. Comparison with the existing nearly-linear phase infinite impulse response low-pass differentiators shows that the low-pass differentiators designed using the proposed method usually require less multiplications, which comes at the cost of a somewhat higher filter order and consequently higher group delay. However, as the reduced number of multiplications lead to lower power consumption if hardware implementation is considered, the proposed low-pass differentiators are an attractive alternative in applications where low group delay is not of crucial importance.

A Grounded Coplanar Waveguide-Based Slotted Inverted Delta-Shaped Wideband Antenna for Microwave Head Imaging

A wideband grounded coplanar waveguide (GCPW) based patch antenna for head imaging is discussed in this paper. The proposed antenna is integrated with a slotted inverted delta-shaped main radiating patch, coplanar waveguide elements, and slotted partial ground. The prime objective of usages of coplanar waveguide elements is enhancing antenna effectiveness. In the prototype, examined different categories of slots in the ground and particularly rectangular and elliptical-shaped slots are used to improve the radiation directivity, gain, and efficiency. The optimized dimension of the antenna is $50\times 44\times 1.524$ mm3 by using the Rogers RO4350B substrate. The measured and simulated results demonstrate that the proposed prototype has a bandwidth of 2.01 GHz (1.70–3.71 GHz) with nearly directional radiation characteristics. The highest gain of the prototype is 5.65 dBi, and the maximum 93% radiation efficiency over the frequency band. The antenna has a lower group delay, higher fidelity factor (>95%), which are significant factors for microwave head imaging. Various design structures are performed to achieve the most satisfactory result. The proposed prototype is designed and analyzed by 3D CST 2019 simulator software. Later, the antenna is fabricated and measured to examine the performance. Thereafter, a single antenna and twelve-antennas array element are configured and placed surrounding the 3D realistic shaped Hugo head model to validate the effectiveness of the single antenna as well as the designed antennas array. The antenna has satisfactory field penetration into the human head tissues with a safe SAR (specific absorption rate). Less than 0.00233 W/kg SAR is attained over the operating frequency range, which is lower than the reported antennas. The Iteratively Corrected Delay Multiply and Sum (IC-DMAS) imaging algorithm will be applied for imaging purposes. The investigation through the literature of the statistical and measured data evident that the proposed antenna is apposite for the wideband microwave head imaging applications.

Compact slot‐loaded ultra‐wideband multiple‐input multiple‐output antenna with fractal‐inspired isolator

In this paper, a compact multielement ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna is presented. The proposed antenna is designed by integrating novel technique of stub-loaded slot, split square ring (SSR), and fractal-inspired isolator. The antenna size is effectively miniaturized by implementing three-sided symmetrical stub-loaded Koch slot and square split ring. The impedance bandwidth is broadened by using small notched partial ground plane. The mutual coupling between the element is impressively reduced by isolating the structure with a Sierpinski fractal. As a result, the proposed antenna achieves a UWB response with a very broad impedance bandwidth of 3.1 to 19 GHz. Moreover, the proposed antenna obtains high peak stable gain and diversity gain of up to 10 dBi, lower group delay (<1 ns), and lower envelop correlation coefficient of <.01. The proposed antenna has electrically small dimensions of 35 × 53 × 0.8 mm. With this low-profile configuration, the proposed antenna is especially a good candidate for portable UWB-MIMO wireless communication system.