Channel Filter Research Articles

Compact High-Isolation LTCC Diplexer Using Common Stub-Loaded Resonator With Controllable Frequencies and Bandwidths

In this paper, a low-temperature co-fired ceramic (LTCC) diplexer is presented with compact size and high isolation. By using the common stub-loaded resonator shared by two channel filters, combining and matching networks are eliminated and only three resonators are used to design the two second-order channel filters, resulting in simple structure and miniaturized size. A novel transmission path is utilized to not only realize the higher channel filter but also prevent the signal at the lower frequency band. And a specific coupling region is selected to simultaneously realize the coupling strength required by lower channel filter and a transmission zero at higher-band frequency. In this way, each channel filter can generate a transmission zero at the passband frequency of the other channel filter, resulting in high isolation. Moreover, the bandwidths and center frequencies of the two channel filters can be individually controlled due to the design flexibility of the multilayer LTCC structure. For demonstration, a diplexer operating at 3.5 and 5.5 GHz is fabricated. The core circuit has the compact size of 1.9 mm $\times1.7$ mm $\times2$ mm or $0.054~\lambda _{g} \times 0.048 \lambda _{g} \times 0.057~\lambda _{g}$ . Within the 3-dB passbands of the lower and higher channel filters, the measured isolation levels are better than 40 and 45 dB, respectively.

Predistortion for Wideband Nonlinear Satellite Downlinks

In this letter, an efficient predistortion scheme is proposed to compensate imperfections in a satellite channel due to the nonlinear power amplifier and the output channel filter. The predistorter is a Wiener system consisting of the linear and nonlinear components, which are trained independently. The predistorter is well suited to systems where the data bits are generated onboard the satellite. The proposed setup effectively compensates the distortions and has lower complexity compared with other strategies.

Selective exclusion and selective binding both contribute to ion selectivity in KcsA, a model potassium channel

The selectivity filter in potassium channels, a main component of the ion permeation pathway, configures a stack of binding sites (sites S1-S4) to which K+ and other cations may bind. Specific ion binding to such sites induces changes in the filter conformation, which play a key role in defining both selectivity and permeation. Here, using the potassium channel KcsA as a model, we contribute new evidence to reinforce this assertion. First, ion binding to KcsA blocked by tetrabutylammonium at the most cytoplasmic site in the selectivity filter (S4) suggests that such a site, when in the nonconductive filter conformation, has a higher affinity for cation binding than the most extracellular S1 site. This filter asymmetry, along with differences in intracellular and extracellular concentrations of K+versus Na+ under physiological conditions, should strengthen selection of the permeant K+ by the channel. Second, we used different K+ concentrations to shift the equilibrium between nonconductive and conductive states of the selectivity filter in which to test competitive binding of Na+ These experiments disclosed a marked decrease in the affinity of Na+ to bind the channel when the conformational equilibrium shifts toward the conductive state. This finding suggested that in addition to the selective binding of K+ and other permeant species over Na+, there is a selective exclusion of nonpermeant species from binding the channel filter, once it reaches a fully conductive conformation. We conclude that selective binding and selective exclusion of permeant and nonpermeant cations, respectively, are important determinants of ion channel selectivity.

Surface plasmon resonance-induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers**Project supported by the National Natural Science Foundation of China (Grant Nos. 61505175 and 61475134) and the Natural Science Foundation of Hebei Province, China (Grant Nos. F2017203110 and F2017203193).

Surface plasmon resonance induced tunable polarization filters based on nanoscale gold film-coated photonic crystal fibers were proposed and analyzed. The characteristics of the polarization filter were calculated by finite element method (FEM). The gold film was selectively coated on the inner wall of one cladding air hole which was located near the fiber core along the y-axis direction. When the phase of core fundamental mode and surface plasmon polaritons (SPPs) mode matches,the two modes couple with each other intensely. Numerical results show that the resonance wavelength and strength vary with fiber structural parameters and the index of the infilling liquid. The fiber parameters were optimized to achieve specific functions. Under the optimal structure, we realized a dual channel filter at the communication wavelength of 1.31 µm and 1.55 µm for y polarization direction and x polarization direction. Then a single channel polarized filter at the communication wavelength of 1.55 µm is also achieved by adjusting the refractive index of the infilling liquid. The proposed polarization filters realized dual channel filtering and single channel filtering simultaneously under the same structure for the first time to the best of our knowledge.

Novel design of ring resonator based temperature sensor using photonics technology

In the present paper, we study the transmission of the two-dimensional photonic crystal (PC) superellipse ring resonator. The fast growing applications of optomechanical systems lead to strong demands in new sensing mechanism in order to design the sensing elements to nanometer scale. The photonic crystal based resonator has been investigated as promising solutions because the band gap structure and resonator characteristics are extremely sensitive to the deformation and position shift of rod / cavity in PC resonators. This structure opens a single channel filter. The study is extended for tuning of channel filter’s wavelength with a temperature of this structure. The transmission of the channel filter shows a red shift with temperature linearly. This wavelength shift of the channel filter is used for the sensor application. The sensitivity for the proposed structure is found to be 65.3 pm/°C. The outstanding sensing capability renders PC resonators as a promising optomechanical sensing element to be integrated into various transducers for temperature sensing applications.

Six‐channel diplexer with compact size and high isolation

A six-channel microstrip diplexer with compact size and high isolation is presented. The six-channel diplexer includes two pairs of multimode resonators with a pseudo-interdigital structure and a distributed coupling feeding line. Modal characteristics of the multimode resonator are explained by the even-odd-mode method. The centre frequencies of channel filters can be controlled independently, while bandwidths can be determined by the coupling coefficient and external quality factor. The distributed coupling feeding line has advantages of size reduction and small loading effect. Therefore, each channel filter can be designed independently. Moreover, the distributed coupling feeding line forms the zero degree feeding structure which can bring transmission zeros to realise high isolation. Finally, a six-channel diplexer prototype working at the centre frequencies of 1.8, 2.4, 3.0, 3.8, 4.7 and 5.8 GHz with over 30 dB isolation is fabricated and measured. Simulated and measured results show a good agreement.

Single image fog and haze removal based on self-adaptive guided image filter and color channel information of sky region

In this paper, we report an effective algorithm for removing both fog and haze from a single image. Existing algorithms based on atmospheric degeneration model generally lead to non-definite solutions for the haze and thick fog images, though they are very efficient for thin fog images. In general, as the algorithms based on vision enhancement cannot automatically adjust weight coefficient for the different structure images, the excessive or inadequate enhancement may emerge. In this paper an original degradation image is primarily segmented into the sky and non-sky regions, and then the main boundaries of non-sky region are extracted using L0 smoothing filter. So our vision enhancement algorithm automatically adjusts weight coefficient according to various structure images. At the stage of vision enhancement, guided image filter famous for its excellent boundary preservation is adopted. As for haze image, the color channel information scattered by haze particles can be obtained in the sky region to make an effective color correction. Both the subjective and objective evaluations of experimental results demonstrate that the proposed algorithm has more outstanding recovery effect for haze and thick fog images. Moreover, the proposed algorithm can judge fog or haze image, which is a by-product of this research.

A compact diplexer with a split-ring resonator junction

Diplexers are three-port filtering devices with a junction connecting two channel filters; the common port connects to an antenna which serves the two channel filters bearing the second and the third port. In the design of diplexers, the technique used in connecting the two channel filters is of great importance to the designers. This is because it determines the size, the effectiveness of signal splitting and combining as well as the ease in implementation. In this paper, an asynchronously tuned double split-ring resonator (SRR) was used in joining the two channel filters. Without incurring any extra space for the junction, the SRR, being a dual-mode resonator, also functioned as a resonant pole for each channel filter. A diplexer operating at 2 GHz and 3 GHz with 4% fractional bandwidths and 20 dB return loss has been demonstrated. The interactions between the SRR and the channel filters were investigated. Good agreement between the simulated and the measured responses was achieved.

Multi-fiber coding on the auditory nerve and the origin of critical-band masking

Understanding the physiological mechanisms that underlie the exquisite frequency discrimination abilities of listeners remains a central problem in auditory science. We describe a computational model of the cochlea and auditory nerve that was developed to evaluate the frequency analysis capabilities of a system in which the output of a basilar membrane filter, transduced into a probability-of-firing function by an inner hair cell, is encoded on the auditory nerve as the instantaneous sum of firings on a critical band of fibers surrounding that filter channel and transmitted to the central nervous system for narrow-band frequency analysis. Performance of the model on vowels over a wide range of input levels was found to be robust and accurate, comparable to the Average Localized Synchronized Rate results of Young and Sachs [J. Acoust. Soc. Am. 1979, 66, 1381-1403]. Model performance in perceptual threshold simulations was also evaluated. The model succeeded in replicating psychophysical results reported in classic studies of critical band masking.

Eosin fluorescence: A diagnostic tool for quantification of liver injury

Hepatitis is one of the most common life threatening diseases. The diagnosis is mainly based on biochemical analysis such as liver function test. However, histopathological evaluation of liver serves far better for more accurate final diagnosis. The goal of our study was to evaluate the eosin fluorescence pattern in CCl4-induced liver injury model compared with normal and different treatment groups. For this purpose, liver tissues were stained with H/E and examined under bright field microscope but the fluorescence microscopy of H/E stained slides provided an interesting fluorescence pattern and was quite helpful in identifying different structures. Interesting fluorescence patterns were obtained with FITC, Texas Red and Dual channel filter cubes that were quite helpful in identifying different morphological features of the liver. During the course of hepatic injury, liver cells undergo necrosis, apoptosis and overall cellular microenvironment is altered due to the modification of proteins and other intracellular molecules. Intensified eosin fluorescence was observed around the central vein of injured liver compared to normal indicating enhanced binding of eosin to the more exposed amino acid residues. To conclude, eosin fluorescence pattern varies with the health status of a tissue and can be used further for the diagnosis and quantification of severity of various liver diseases.

Tune-All RF Planar Duplexers With Intrinsically Switched Channels

A class of frequency-agile planar duplexers with independently controllable channels in terms of center frequency, passband-width, out-of-band power-attenuation characteristics, and tune-all transfer-function capabilities is reported. Each channel filter is made up of frequency-reconfigurable resonators that are coupled to its direct input-to-output electrical path through static impedance inverters and generate power transmission zeros (TZs). Thus, the duplexer channels are exclusively reconfigured by means of dynamic TZ allocation. Furthermore, the channel filters can be intrinsically switched-OFF by incorporating a bandstop-filtering function into them. The operational principles of this spectrally adaptive duplexer concept are expounded and experimentally demonstrated through the manufacturing and characterization of a microstrip prototype in the UHF range.

Design of quad-channel diplexer adopting channel filters with impedance transformers

Design of quad-channel diplexer adopting channel filters with impedance transformers

A Compact Substrate Integrated Waveguide Diplexer Using Dual Mode Resonator as a Junction for System in Package Applications

ABSTRACTIn this article, a simple single-layer substrate integrated waveguide diplexer is proposed in which a dual mode cavity is used as a junction. A square substrate integrated waveguide cavity with corner cut perturbation is as the dual mode cavity and the odd and even modes of this cavity are a part of the receiver and transmitter channel filters, respectively. These two modes are coupled to the other sections of the receiver and transmitter filters in such a way that the designed receiver and transmitter filters are independent from each other. The diplexer coupling diagram is studied and characteristic polynomials of the diplexer are obtained based on the characteristic polynomials of receiver and transmitter channel filters. The proposed diplexer provides high isolation between two passbands and also has a compact size; therefore, it can be suitable as a section of a system on substrate. A prototype diplexer is fabricated by a printed circuit board process on a single layer. Design process and simulated and measured results of the fabricated diplexer are presented.

Ultra-wide tuning single channel filter based on one-dimensional photonic crystal with an air cavity**Project supported by the National Natural Science Foundation of China (Nos. 61575138, 61307069, 51205273), and the Top Young Academic Leaders and the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi.

By inserting an air cavity into a one-dimensional photonic crystal of LiF/GaSb, a tunable filter covering the whole visible range is proposed. Following consideration of the dispersion of the materials, through modulating the thickness of the air cavity, we demonstrate that a single resonant peak can shift from 416.1 to 667.3 nm in the band gap at normal incidence by means of the transfer matrix method. The research also shows that the transmittance of the channel can be maximized when the number of periodic LiF/GaSb layers on one side of the air defect layer is equal to that of the other side. When adding a period to both sides respectively, the full width at half maximum of the defect mode is reduced by one order of magnitude. This structure will provide a promising approach to fabricate practical tunable filters in the visible region with ultra-wide tuning range.

Compact Quad-Band Bandpass Filter Using Double-Diplexing Structure

AbstractThis paper presents a compact quad-band bandpass filter (QB-BPF) using double-diplexing structure, which consists of two channel filters and a pair of modified manifold-coupled lines. Each channel filter is realized by the asymmetrical coupling shorted stub loaded stepped-impedance resonator (SSLSIR) dual-band bandpass filter (DB-BPF), and the modified manifold line constructed by lumped elements is proposed to connect two channel filters to constitute the QB-BPF. The fabricated QB-BPF occupies a compact circuit size of 0.178λ

Analysis of circulating tumor cells from lung cancer patients with multiple biomarkers using high-performance size-based microfluidic chip.

Circulating tumor cells (CTCs) have attracted pretty much attention from scientists because of their important relationship with the process of metastasis. Here, we developed a size-based microfluidic chip containing triangular pillar array and filter channel array for detecting single CTCs and CTC clusters independent of tumor-specific markers. The cell populations in chip were characterized by immune-fluorescent staining combining an epithelial marker and a mesenchymal marker. We largely decreased the whole time of detection process to nearly 1.5h with this microfluidic device. The CTCs were subsequently measured in 77 patients with lung cancer and 39 healthy persons. The microfluidic device allowed for the detection of CTCs with apparent high sensitivity and specificity (82.7% sensitivity and 100% specificity). Furthermore, the total CTC counts were found to be elevated in advanced patients with metastases when compared with those without (20.89±14.57 vs 8.428±5.858 cells/mL blood; P<0.01). Combined epithelial marker and mesenchymal marker analysis of CTCs could provide more information about metastasis in patients than only usage of epithelial marker. In conclusion, the development of the size-based microfluidic device for efficient capture of CTCs will enable detailed characterization of their biological properties and values in cancer diagnosis.

Optical band-stop filter and multi-wavelength channel selector with plasmonic complementary aperture embedded in double-ring resonator

A compact nanoscale wavelength band-stop filter with aperture embedded in double-ring resonator is proposed and numerically investigated by using Finite-Difference Time-Domain (FDTD) method. With a narrow aperture created between embedded double rings, the modes of the split-ring cavity can be modulated by the aperture in different manners when the parameters of the aperture are changed. Furthermore, the absorption peaks of resonator modes can be selectively inhibited by altering the positions of the aperture without changing outer size of the resonator. Based on above characteristics, a 1×2 multiple-contact channel selector is designed with a rotating aperture which can select the output waveguide. The proposed filter and selector have potential applications in highly integrated optical circuits.

One-step synthesis of organic microwire-disk interconnected structure for miniaturized channel filters

Miniaturized channel filters are in high demand for many applications such as photonic integrated circuits, information-based technology, and platforms for investigation of light–matter interactions. Recently, several photonic schemes have been proposed to achieve nanofilters, which require sophisticated growth techniques. Here, we have fabricated microdisk whispering-gallery-mode (WGM) resonators through controlled assembly of organic materials with an emulsion-solvent-evaporation method. Based on this emulsion assembly method, the diameters of microdisks can be easily controlled, and more importantly, a microwire-disk interconnected structure is able to be constructed via one-step assembly. This microwire-waveguide-connected microdisk heterostructure can be utilized as a channel drop filter. Our results have demonstrated a facile way to achieve flexible WGM-based photonic components which can be integrated with other functional devices.

OFDM symbol detection integrated with channel multipath gains estimation for doubly-selective fading channels

Orthogonal Frequency Division Multiplexing (OFDM) is a technique for wideband transmission that is commonly used in modern wireless communication systems because of its good performance over frequency selective channels. However OFDM systems are sensitive to channel time variations resulting in Inter-Carrier Interference (ICI), that without suitable detection methods can degrade performance significantly. Channel State Information (CSI) is essential to various OFDM detection schemes, and its acquisition is a critical factor over time varying channels. This work considers a Kalman filter channel multipath gains estimation technique for time varying environments, integrated with a novel detection scheme for OFDM based on a Sphere Decoding (SD) algorithm derived to exploit the banded structure of the channel matrix. This combined scheme employs decision–feedback from the SD requiring only a low pilot symbol density, and hence improves bandwidth efficiency. Three techniques for integrating the Kalman filter operating in decision–feedback mode, with SD data detection that produces these decisions, are considered in this paper. When compared with other competing schemes, this integrated symbol detection and channel multipath gains estimation approach for OFDM provides performance advantages over time varying channels. Furthermore, it is shown that for moderate Doppler shifts the degradation that carrier phase noise induces in this scheme is small.

Design of Microstrip Low-Pass–Bandpass Multiplexers Using Distributed Coupling Technique

In this paper, a five-channel low-pass–bandpass frequency quintplexer and a five-channel low-pass–bandpass frequency triplexer are presented. The multiplexer consists of a long distributed coupling feeding line, output feeding lines, a low-pass filter, and four bandpass channel filters. To validate the design concept, the two multiplexers are designed, fabricated, and tested, where the simulation results agree well with measurement results.