Passband Region Research Articles

Continuous-time analog filter with passband constant IIP3 based on common-gate amplifier

This paper presents an analog filter based on Rauch biquadratic cell. The filter exploits an improved analog stage that makes linearity performance uniform over the entire pass-band frequency region. All feedback analog filters suffer from poor linearity when the input tones frequency is in close proximity to the closed-loop poles frequency, where loop-gain reduces. This often forces an overdesign with higher current (higher power consumption) and/or higher overdrive voltages (lower dynamic range) in order to meet the linearity specifications over the whole filter pass-band region. The hereby proposed Rauch scheme resolves such a binding issue without power increasing and having the same IIP3 at low and at high frequency (up to the filter closed-loop poles frequency). Hence the linearity performance is in first approximation independent on the input tones bandwidth. In order to validate the hereby proposed idea a 4th-order 25 MHz −3 dB bandwidth pseudo-differential filter has been designed and simulated in CMOS 28 nm technology. The prototype consumes 820 µW from 1 V supply voltage and has 15 and 13 dBm IIP3 at 5 and 6 and 20 and 21 MHz input tones, respectively.

A reflective-type, quasi-optical metasurface filter

We introduce a new technique for designing quasi-optical, reflective-type spatial filters. The proposed filter is a reflective metasurface with a one dimensional, frequency-dependent phase gradient along the aperture. By careful design of each unit cell of the metasurface, the phase shift gradient provided by the adjacent unit cells can be engineered to steer the beam towards a desired, anomalous reflection direction over the passband region of the filter. Outside of that range, the phase shift gradient required to produce the anomalous reflection is not present and hence, the wave is reflected towards the specular reflection direction. This way, the metasurface acts as a reflective filter in a quasi-optical system where the detector is placed along the direction of anomalous reflection. The spectral selectivity of this filter is determined by the frequency dispersion of the metasurface's phase response. Based on this principle, a prototype of the proposed metasurface filter, which operates at 10 GHz and has a bandwidth of 3%, is designed. The device is modeled using a combination of theoretical analysis using the phased-array theory and full-wave electromagnetic simulations. A prototype of this device is also fabricated and characterized using a free-space measurement system. Experimental results agree well with the simulations.

Design of digital IIR filter with low quantization error using hybrid optimization technique

In this paper, a hybrid optimization technique based on particle swarm optimization (PSO) and artificial bee colony (ABC) algorithm is presented for the optimal design of infinite impulse response (IIR) filter with low quantization effect. In this method, different variants of PSO have been exhaustively tested, and the time varying coefficients-PSO (TVC-PSO) is used to formulate a new hybrid technique for better exploitation and exploration, which is further modified by sorting and replacement mechanism of Scout Bee from ABC algorithm. For designing IIR filter, an objective function is constructed that satisfies the absolute error including peak ripples in passband and stopband regions in frequency domain, while stability of designed filter is confirmed by exploiting the lattice form structure during iterative computation that also reduces computation complexity. Several attributes such as passband error $$(e_{\mathrm{p}})$$ , stopband error $$(e_{\mathrm{s}})$$ , and stopband attenuation $$(A_{\mathrm{s}})$$ are used to measure the performance of proposed algorithm. The simulation results presented in this paper evidence that this technique can be effectively used for designing digital IIR filter with higher filter taps, and low quantization effect for fixed number of bits.

Compact lowpass filter with flat group delay using lattice‐shaped resonator

A compact lowpass filter (LPF) using a lattice-shaped resonator is presented with a wide rejection band and sharp roll-off. The designed LPF has −3 dB cut-off frequency at 4.34 GHz. The fabricated LPF is simulated and tested; there is a good agreement between the simulation and experimental results. Experimental results show that the maximum variation of flat group delay is only 0.3 ns in the passband. Also, the measured return-loss and insertion loss are more than 19 dB and <0.1 dB in 88% of the passband region, respectively. The size of the designed filter is only 22.5 × 8.65 mm2.

Study of backward waves in multilayered structures composed of graphene micro-ribbons

In this paper, the multilayered structure composed of periodic arrays of graphene ribbons separated by the dielectric slabs is investigated for both the transverse electric (TE) and transverse magnetic (TM) polarizations. The transmission spectra show a stopband region between the low-THz frequency passband region and the higher-frequency one for TM polarization due to dual capacitive-inductive nature of the surface impedance corresponding to arrays of graphene ribbons. For TE polarization, the surface impedance is pure inductive; therefore, a passband region can be seen after the low-THz frequency stopband region. The in-plane permittivities are calculated based on the scattering parameters retrieval method. The negative permittivities are obtained in stopband regions corresponding to Bloch evanescent modes. This structure allows the propagation of backward waves in negative permittivity regime for TM polarization.

Investigation of New Microstrip Bandpass Filter Based on Patch Resonator with Geometrical Fractal Slot.

A compact dual-mode microstrip bandpass filter using geometrical slot is presented in this paper. The adopted geometrical slot is based on first iteration of Cantor square fractal curve. This filter has the benefits of possessing narrower and sharper frequency responses as compared to microstrip filters that use single mode resonators and traditional dual-mode square patch resonators. The filter has been modeled and demonstrated by Microwave Office EM simulator designed at a resonant frequency of 2 GHz using a substrate of εr = 10.8 and thickness of h = 1.27 mm. The output simulated results of the proposed filter exhibit 22 dB return loss, 0.1678 dB insertion loss and 12 MHz bandwidth in the passband region. In addition to the narrow band gained, miniaturization properties as well as weakened spurious frequency responses and blocked second harmonic frequency in out of band regions have been acquired. Filter parameters including insertion loss, return loss, bandwidth, coupling coefficient and external quality factor have been compared with different values of perturbation dimension (d). Also, a full comparative study of this filter as compared with traditional square patch filter has been considered.

Design of computationally efficient 2D FIR filters using sampling‐kernel‐based interpolation and frequency transformation

A closed-form design of a two-dimensional (2D) finite impulse response (FIR) filter with circular, rectangular, fan or quadrant-fan shapes in the passband region is presented. The computationally efficient 2D FIR filter can be implemented using frequency transformation and sampling-kernel-based interpolation instead of an optimisation algorithm. When compared with the existing method, the proposed method reduces 90% of multiplications for filtering. Several design examples are demonstrated to verify the performance of the proposed design.

Compact microstrip lowpass filter with very sharp roll-off and ultra-high figure-of-merit for wireless applications

This study presents a novel lowpass filter (LPF) with very sharp roll-off and ultra-high figure-of-merit (FOM). The −3 dB cutoff frequency of the proposed LPF is set nearby 1.39 GHz to eliminate the higher frequencies for wireless applications in communication systems. The measurement results indicated that the transition band of the proposed LPF is 0.04 GHz from −3 dB to −20 dB and 0.06 GHz from −3 dB to −40 dB, which shows a very sharp roll-off. Also, an ultra-wide stopband from 1.39 GHz to 20.2 GHz and low insertion loss and high return loss in the passband region are achieved. The proposed LPF has an ultra-high FOM which is probably the highest FOM ever reached in related works until 2014, thus showing its strong sufficiency. The proposed LPF is fabricated and tested, and there is a good agreement between the simulation and measured results.

Green Color Purification in Tb(3+) Ions through Silica Inverse Opal Heterostructure.

The ordered SiO2:Tb(3+) inverse opal heterostructure films are fabricated through polystyrene spheres hetero-opal template using the convective self-assembly method to examine their potential for color purification. Their optical properties and photoluminescence have been investigated and compared with individual single inverse opals and reference (SiO2:Tb(3+) powder). The heterostructures are shown to possess two broad photonic stop bands separated by an effective pass band, causing suppression of blue, orange, and red emission bands corresponding to (5)D4 → (7)F(j); j = 6, 4, 3 transitions, respectively and an enhancement of green emission (i.e., (5)D4 → (7)F5). Although the suppression of various emission occurs because of its overlap with the photonic band gaps (PSBs), the enhancement of green radiation is observed because of its location matching with the pass band region. The Commission International de l'Eclairage (CIE) chromaticity coordinates of the emission spectrum of the heterostructure based on polystyrene sphere of 390 and 500 nm diameter are x = 0.2936, y = 0.6512 and lie closest to those of standard green color (wavelength 545 nm). In addition, a significant increase observed in luminescence lifetime for (5)D4 level of terbium in inverse opal heterostructures vis-à-vis reference (SiO2:Tb(3+) powder) is attributed to the change in the effective refractive index.

Dual-Band Ring Coupler Based on the Composite Right/Left-Handed Folded Substrate-Integrated Waveguide

In this letter, a dual-band ring coupler based on the folded substrate-integrated waveguide (FSIW) is proposed. The artificial structure, the composite right/left-handed (CRLH) transmission lines were implemented in the FSIW by loading the interdigital capacitors in the middle metallic layer to generate a left-handed passband region below the cutoff frequency of the ordinary waveguide ${\rm TE}_{10}$ mode for coupler miniaturization. The FSIW is the folded counterpart of the substrate-integrated waveguide (SIW) and thus can prevent the CRLH transmission lines from radiation loss by shielding the interdigital capacitors in the waveguide. Besides, the FSIW-based coupler is able to eliminate the electromagnetic interference (noise) with adjacent objects and lend itself to multilayer circuit integration. A ring coupler that operates at 4.3 and 7.6 GHz was developed and experimentally verified. To the best of the authors' knowledge, it is the first time that a dual-band rat-race was implemented and reported based on the CRLH-FSIW structure.

Study and Fabrication of Filter Film in Tactical Optical Fiber Communication System

The development of optical fiber transmission technology provides a broad application prospect for the communication of real-time battlefield information. The information could be communicated between the front and headquarters through the cable by using tactical optical fiber communication system, which ensures the missions of military intelligence communicated and tactical real-time arrangement are completed successfully. According to the requirements of multiplexer for military tactical optical fiber communication system, the filters with low-loss have been developed. Filters are prepared by the depositing method of dual ion beam sputtering, Nb2O5 and SiO2 have been chosen as deposition materials, and the filter film is designed and optimized with the help of TFCalc software. In order to broaden the shortwave cutoff region of the filter, the long-wave pass film have been added behind the initial film, and the thickness of the matching layers have been optimized, which based on the concept of equivalent refractive index, the insertion loss of the pass-band of the filter has been reduced. The optical extreme value method and average time method have been used to control layers thickness, and the problem of the layers thickness accuracy controlling have been solved by using the method of real-time calibration of the deposition rate and the repeatability of parameters accurately control. The transmission spectrum of the filter has been tested, which demonstration that the center wavelength of the filter is 1511.2nm, the width of the filters pass band is 17.1nm and 23.5nm in the region of-0.5dB and-35dB respectively, the worst insertion loss within pass band region is-0.1dB, the ripple of the pass band is 0.06dB. The results show that the preparation of the filter meets the using requirements of military tactical fiber optic communication system well.

Optimal Sharpening of Compensated Comb Decimation Filters: Analysis and Design

Comb filters are a class of low-complexity filters especially useful for multistage decimation processes. However, the magnitude response of comb filters presents a droop in the passband region and low stopband attenuation, which is undesirable in many applications. In this work, it is shown that, for stringent magnitude specifications, sharpening compensated comb filters requires a lower-degree sharpening polynomial compared to sharpening comb filters without compensation, resulting in a solution with lower computational complexity. Using a simple three-addition compensator and an optimization-based derivation of sharpening polynomials, we introduce an effective low-complexity filtering scheme. Design examples are presented in order to show the performance improvement in terms of passband distortion and selectivity compared to other methods based on the traditional Kaiser-Hamming sharpening and the Chebyshev sharpening techniques recently introduced in the literature.

Design of optical notch filters using apodized thickness modulation

An apodized thickness design method for discrete layer notch filters is presented. The method produces error tolerant designs with low ripple in the passband regions without any additional numerical optimization. Several apodization functions including Gaussian, cosine squared, as well as quintic are considered. Theoretical and experimental results from ion beam deposited sample designs for single-notch as well as multinotch filters are presented. Good agreement is observed between the theoretical design and the experimental measurement even when the deposition process is only controlled on time. This demonstrates the low layer error sensitivity of the apodized designs.

Suppression of bending waves in a periodic beam with timoshenko beam theory

Active control of bending waves in a periodic beam by the Timoshenko beam theory is concerned. A discussion about the possible wave solutions for periodic beams and their control by forces is presented. Wave propagation in a periodic beam is studied. The transfer matrix between two consecutive unit cells is obtained based on the continuity conditions. Wave amplitudes are derived by employing the Bloch-Floquet theorem and the transfer matrix. The influences of the propagating constant on the wave amplitudes are considered. It is shown that vibrations are still needed to be suppressed in the pass-band regions. Wave-suppression strategy described in this paper is employed to eliminate the propagating disturbance of an infinite periodic beam. A minimum wave-suppression strategy is compared with the classical wave-suppression strategy.

An improved particle swarm optimization method for multirate filter bank design

In this paper, a new particle swarm optimization (PSO) based method is proposed for the design of a two-channel linear phase quadrature mirror filter (QMF) bank in frequency domain. The origional particle swarm optimization technique is modified by introducing the concept of Scout Bee from Artificial Bee Colony (ABC) technique for designing a low pass prototype filter having ideal filter characteristics in the passband and stopband regions, and its magnitude response at quadrature frequency is 0.707. The design problem is formulated as a linear combination of passband error and residual stop band energy of the low pass filter, and the square error of the overall transfer function of the QMF bank at the quadrature frequency π/2, in the transition band. The design results included in the paper clearly show the improvement of the proposed PSO technique over earlier reported results.

THEORY AND REALIZATION OF SIMPLE BANDPASS FILTERS WITH ANTIPARALLEL CONFIGURATION

This paper introduces a theoretical analysis as well as a design example for bandpass fllters (BPF) with a distinctive topology. Based on the analysis of simple two-port symmetrical lossless networks with a parallel structure, a method for obtaining normalized BPF prototypes with desired bandwidths was developed. These prototypes can be scaled to any central frequency and symmetrical real termination in the same way as conventional fllters. It is also demonstrated that with a slight modiflcation of the basic BPF prototypes, transmission zeros with controllable frequencies can be introduced in both the lower and the upper stopband region. Such modifled prototypes are more convenient for the realization of printed fllters than the basic BPF prototypes. The proposed fllters have almost identical characteristics in the broad vicinity of the passband region either when composed of ideal lumped elements or of transmission lines (TLs). Due to its simplicity, the proposed concept could be applied for the realization of a printed BPF at a large variety of PCB types, substrates and practical design conflgurations. A microstrip BPF model is realized for the experimental veriflcation of the presented theory. The measured and theoretical results show excellent agreement, conflrming the proposed concept and the exactness of the methodology.

Novel droop-compensated comb decimation filter with improved alias rejections

This paper presents a novel two-stage comb decimator with the improved magnitude characteristic. Simple multiplierless corrector filters, which are designed using the frequency sampling and IFIR methods, are introduced. The proposed filters compensate the comb passband droop in the wideband passband region and increase the attenuations in the folding bands. Using the multirate identity the filters may be moved to a lower rate. The filter design depends only on the number of the cascaded comb filters and do not depend on the decimation factor M.

Narrow line-width filters based on rugate structure and antireflection coating

Filters that have high transmittance over the passband region of the reflectance spectrum are designed by combining rugate structures and antireflection (AR) coatings. It is found that, under certain conditions, the refractive index of the substrate could be “converted” to the air-side refractive index of the graded-refractive-index coating. A method for the fabrication of graded-index coatings by rapidly alternating deposition of low (SiO2) and high (Nb2O5) refractive index materials is introduced, and this technology was used to fabricate a rugate structure. An AR coating with a refractive index of 1.23 was grown onto the rugate structure by glancing angle deposition technology. Optical measurements of the combined structure show excellent transmittances over the wavelength regions around the reflection band and high reflectances in the stopband.

A hybrid method for designing linear-phase quadrature mirror filter bank

In this work, a hybrid method in frequency domain for design of a linear-phase quadrature mirror filter bank is proposed. The nonlinear least square hybrid method based on Levenberg-Marquardt (LM) and Quasi-Newton (QN) is developed for the design of a low-pass prototype filter whose responses in the passband and stopband are ideal, and the filter bank response at quadrature frequency is 0.707. The proposed method is employed to optimize the quadratic measure of ideal characteristics of the prototype filter and filter bank at quadrature frequency. Performance and effectiveness of the proposed method in terms of peak reconstruction error (PRE), mean squares error in passband and stopband regions, and error in transition band at quadrature frequency are shown through numerical examples and comparison of the results with other existing method. It was found that the proposed method is very simple and easy to implement for QMF bank design problem.

Sharp Transition Multiband Filter in Speech Processing Scheme for Hearing Impaired

Problem statement: A simple analytical approach to the synthesis of a sharp transition, linear phase, multiband FIR filter is presented. The filter magnitude response is modeled using trigonometric functions of frequency. Approach: Employing variable density of ripple cycles in passband and stopband regions with large density of ripples cycles at the sharp transition edges, reduces the abrupt discontinuities at these edges. Results: As a result, Gibb’s phenomenon is reduced in the filter implementation thus giving a flat passband and good stopband attenuation. A closed form expression for impulse response coefficients is obtained. The filter design is easily tunable and allows for variation in transition bandwidth of each band. A speech processing scheme is implemented using a pair of the proposed sharp transition multiband FIR filters to split the speech spectrum into complementary short time spectral bands. Conclusion: The adjacent speech formants are fed dichotically to the two ears to reduce the effect of spectral masking and hence improve speech perception in sensorineural hearing impaired.