Bandpass Channels Research Articles

High‐isolation single‐layer dual‐mode substrate‐integrated waveguide diplexers for millimetre‐wave applications

AbstractNew coupling scheme substrate‐integrated waveguide (SIW) diplexers based on dual‐mode cavities are proposed for millimetre‐wave applications. Dual‐mode SIW cavities are simultaneously employed in common input and coupling cavity to produce filtering transmission poles and transmission zero (TZ). A common input SIW cavity with two orthogonal modes is employed instead of the traditional T‐junction for circuit miniaturisation, insertion‐loss reduction, and intrinsically high isolation. A critical dual‐mode SIW cavity with diagonally distributed modes has been employed in each channel to realise a controllable stopband TZ for high selectivity of passband's skirt. To further improve channel isolation and passbands' selectivity, a SIW diplexer based on dual‐ and single‐mode cavities is proposed, and four‐pole responses for each passband channel are designed. For the verification, two millimetre‐wave diplexers have been fabricated and tested.

Ensemble-based feature engineering mechanism to decode imagined speech from brain signals

Speech impairments, resulting from brain injuries, mental disorders, or vocal abuse, substantially affect an individual’s quality of life and can lead to social isolation. Brain–Computer Interfaces (BCIs), particularly those based on EEG, offer a promising support mechanism by harnessing brain signals. Owing to their clinical efficacy, cost-effective EEG devices, and expanding applications in the medical and social spheres, their usage has surged. This study introduces an ensemble-based feature engineering mechanism to pinpoint the optimal brain rhythm, channel subset, and feature set for accurately predicting imagined words from EEG signals via machine learning models. Leveraging the 2020 International BCI competition dataset, we employed bandpass filtering, channel wrapping, and ranking methods were applied to discern suitable brain rhythms and features associated with imagined speech. Subsequent application of kernel-based principal component analysis enabled us to compress the feature space dimensionality. We then trained various machine learning models, among which the kNN model excelled, achieving an average accuracy of 73% in a 10-fold cross-validation scheme ,surpassing 18% higher than the existing literature. The Gamma rhythm was identified as the most predictive of imagined speech from EEG brain signals. These advancements herald a new era of more precise and effective BCIs, poised to significantly improve the lives of those with speech impairments.

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.

High-speed wavelength interrogation system based on crossed HiBi-FLMs for array FBGs

A novel ultrafast wavelength interrogation system for array fiber Bragg gratings (FBGs) has been proposed and experimentally demonstrated, the operation principle is based on pulsed optical source (POS) combined with edge-filtering method and time-division multiplexing (TDM) technique. Thanks to the Gaussian-shape nature and numerous passband channels of the HiBi-FLM transmission, the simultaneous interrogation of array wavelength-division multiplexing (WDM) FBGs can be realized by employing crossed HiBi-FLMs scheme. The HiBi-FLM can provide an individual edge filter for each WDM-FBG and map the FBG reflection spectra into corresponding optical intensity, thus realizing the simultaneous interrogation of multiple WDM-FBGs. The interrogation speed of the proposed system is as high as 200 kHz, which can be further improved to hundreds of megahertz (MHz) by increasing the repetition rate of the POS, the response speed of the photodetector (PD), and the sampling rate of field programmable gate array (FPGA), as well as reducing the pulse width and the lengths of the delay lines. The proposed wavelength interrogation system features high speed, outstanding multiplexing capability, large dynamic range and simple configuration, thus providing a promising solution for various applications, such as quasi-distributed sensing, high-speed communication, medical treatment and the monitoring of ultrafast dynamic phenomena (e.g., molecular dynamics sensing and aircraft engine diagnostics).

A Fully Integrated Controllable Bandpass Filter With a Constant Q-Factor for Ultrasonic Applications

In this paper, a tuneable low-power active bandpass filter (BPF) is designed for channel selection in TSMC’s 65-nm CMOS technology. The proposed filter consists of two identical BPFs which are based on a gm-C topology, and can be controlled with a constant quality factor. The center frequency of this design can be changed to acquire a specific passband channel from 60 kHz to 2.5 MHz by adjusting the bias voltage in discrete increments, with an almost constant quality factor equal to 7.2. To validate the design, the integrated circuit and a test board are fabricated. Five passband channels are measured from the proposed design with a low power consumption equal to 68 ‘W. The measured dynamic range is equal to 51.6 dB when the total harmonic distortion (THD) is equal to 1%. Hence, the proposed controllable channel selection filter shows an excellent performance as compared to existing work and offers a great potential for use applications with heterogeneous sensor nodes.

Millimeter split ring filter for 5G application

This paper is about designing a split ring filter for the 5G applications. The framework of band pass channels is the major consideration of the design. The band pass channel allows only the corresponding band and rejects all other frequency bands. In the aspect of filter design, there are two significant variables such as size and effectiveness that are taken into account for deploying it in a portable 5G application. These constraints show the plan, recreation and creation of a pass band channel with the recurrence scope from 26 to 28 GHz. The designed filter for the channel can be utilized as the front finish for the down conversion of millimeter wave to microwave frequencies of 2–18 GHz.

Miniaturized Diplexers With Large Frequency Ratios Based on Common Half-Mode Dual-Mode SIW Junction-Cavities

Miniaturized substrate integrated waveguide (SIW) diplexers with widely separated channel passbands using common half-mode dual-mode SIW junction-cavities are presented and developed for 5G sub-6 GHz communications and wireless systems. With this kind of half-mode dual-mode junction-cavities to eliminate the conventional T-junctions and also to produce one transmission pole in each channel passband, significant circuit miniaturization can be achieved for SIW diplexers. Additionally, by exploiting the first dual modes in the half-mode SIW junction-cavities, flexibly allocated fractional bandwidths (FBWs) for the two channels can be realized through FBW design graphs, large frequency ratios can also be accommodated, which is difficult to implement using the whole-mode SIW cavity scheme due to spurious problems. Two compact SIW diplexers with large frequency ratios are synthesized, designed, fabricated, and measured for demonstration, including a third-order direct-coupled prototype centered at 3.5 and 5.0 GHz with a frequency ratio of 1.43 based on the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> /TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">301</sub> half-mode dual-mode junction-cavity and a fourth-order cross-coupled prototype centered at 3.5 and 5.5 GHz with a frequency ratio of 1.57 based on the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> /TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> half-mode dual-mode junction-cavity.

Performance of Oversampled Polyphase Filterbank Inversion via Fourier Transform: Continuous Signals

Signal channelization enables efficient frequency domain processing and is a mainstay of astronomical signal processing, but applications that require high time resolution necessitate reconstruction of the original wide band signal. In a previous paper, a near-perfect method of reconstructing a time-limited input signal from the output of an oversampled polyphase filterbank (PFB) was described. Here, we consider the case where continuous signals are processed. We show that the most simplistic approach, which utilizes non-overlapping windows and a fast Fourier transform (FFT) channelizer, introduces large errors whose magnitude can equal the signal. The ringing introduced by truncation at the end of a block, combined with the cyclic nature of FFTs, leads to errors that are concentrated at block boundaries. These localized errors can be heavily suppressed by utilizing overlapping windows and nearly completely eliminated by apodizing the data blocks with a Tukey window. After these improvements, the much smaller residual error is concentrated at the PFB channel boundaries and is due to adjacent channels having different gain slopes at the channel boundary. Increasing the channel passband equalizes the gain slope at the channel boundary, and the error is reduced further. With these changes, errors as low as −100[Formula: see text]dB are achieved, and the method of reconstructing the channelized data meets the stringent signal purity requirement for astronomical applications such as radio pulsar timing.

Tunable wide bandstop and narrow bandpass filters based on one-dimensional ternary photonic crystals comprising defects of silver nanoparticles in water

In this study, we propose a novel structure comprising a one-dimensional photonic crystal of ZnSe/Nb2O5/BK7 as a tunable wide bandstop filter to cover the visible range of 500–800 nm. The transmittance spectrum of the structure was numerically investigated using the transfer matrix method. A stopband covering the range of 609–682 nm was obtained when the structure had nine ternary unit cells. The range widened to cover 576–707 nm when the number of unit cells increased to 20. A narrow bandpass filter was obtained when a defective layer comprising silver nanoparticles dispersed in water was inserted in the middle of the photonic crystal. We demonstrated the tuning of the single bandpass channel by considering the dispersion of the materials due to the modulation of the filling factor and size of the silver nanoparticles as well as the angle of incidence for radiation. The resonant peak with a transmittance of more than 0.85 obtained at normal incidence shifted from 620.8 to 644.5 nm within the bandgap as the filling factor increased from 0.0 to 0.10. We also found that the resonant peak shifted slightly (from 631.5 to 632.4 nm) when the radius of the silver nanoparticles increased from 1.0 to 15.0 nm. In addition, when the angle of incidence increased from 10° to 80°, the resonant peak shifted from 630.0 to 545.8 nm. Therefore, the proposed structure is promising for fabricating practical tunable wide bandstop and single-channel bandpass filters in the visible region.

Compact filtering crossover design based on SIW quintuple‐mode resonators

AbstractA compact filtering crossover utilizing substrate integrated waveguide (SIW) quintuple‐mode resonator (QMR) technology is proposed for the first time. Benefiting from this technology, the proposed crossover firstly breaks the status quo that SIW crossover filtering response is only concentrated in single passband, thereby extending the applications of the SIW crossovers. In design, the QMR is derived by embedding metal‐via holes in the conventional SIW resonant cavity, thus to produce quintuple resonant modes featuring with specific electric distributions. Next, by dividing these modes into two groups, a triple‐mode bandpass filter (BPF) channel and a single‐mode dual‐band BPF channel are both realized. To implement two flat passband channels, there are two SIW cavities cascaded. And also, the isolation between two channels is implemented by employing the orthogonal characteristic. In this way, a crossover is implemented. The proposed design method can be a good candidate for developing SIW multi‐band filtering crossovers. For verification, an example circuit has been designed, fabricated, and measured.

Identification of Nonlinear Channels in Bandpass Communication Systems with OFDM Inputs

A general approach to the derivation of simple yet accurate formulas for identifying bandpass nonlinear channels in or-thogonal frequency-division multiplexing (OFDM) systems is proposed in this paper. The OFDM is an widely adopted tech-nique for wideband communication applications. An OFDM signal could be highly vulnerable to nonlinearities in a com-munication link. This makes proper estimation of the nonlin-ear channel essential for an OFDM system. A nonlinear bandpass communication channel is commonly described by a complex Voletrra series, in which the task of nonlinear channel identification is to determine the Volterra kernels. This task can become very difficult when the order of the nonlinear system increases. In this paper, we explore higher-order sta-tistical properties of the OFDM signal to develop a universal scheme for solving the Volterra kernel identification problem. Based on this scheme, a simple yet accurate formula for identifying Volterra kernels of 5th-order nonlinear OFDM systems is derived. The resulting solution is shown to attain the minimum mean square error (MMSE) in both theory and computer simulation.

Differential Evolution Algorithm for Ship Path Planning in Open Waters

A general approach to the derivation of simple yet accurate formulas for identifying bandpass nonlinear channels in or-thogonal frequency-division multiplexing (OFDM) systems is proposed in this paper. The OFDM is an widely adopted tech-nique for wideband communication applications. An OFDM signal could be highly vulnerable to nonlinearities in a com-munication link. This makes proper estimation of the nonlin-ear channel essential for an OFDM system. A nonlinear bandpass communication channel is commonly described by a complex Voletrra series, in which the task of nonlinear channel identification is to determine the Volterra kernels. This task can become very difficult when the order of the nonlinear system increases. In this paper, we explore higher-order sta-tistical properties of the OFDM signal to develop a universal scheme for solving the Volterra kernel identification problem. Based on this scheme, a simple yet accurate formula for identifying Volterra kernels of 5th-order nonlinear OFDM systems is derived. The resulting solution is shown to attain the minimum mean square error (MMSE) in both theory and computer simulation.

Design and Fabrication of an Integrated Dual-Channel Thin-Film Filter for the Mid-Infrared

Micro-filters fabricated using integration methods is now the trend for multichannel filters in imaging spectrum systems. Traditional multichannel bandpass filters are mainly fabricated separately by multilayered thin films and then glued together. This approach involves the complexity of precision cutting, dicing, and adhesive bonding; therefore, the possibility of miniaturization is quite limited. In this work, a dual channel bandpass thin film filter for the mid-infrared was fabricated by using the lift-off process. The structure of a 4-cavity Fabray–Perot (F-P) type filter was designed and optimized. The bandpass filter over the range 3.55–3.75 µm with full width at half maximum (FWHM) of 274 nm and the bandpass filter over the range 4.85–4.95 µm with FWHM of 246 nm were obtained with a 4.5 µm joint width. The average transmittance of the filters is more than 83.5% and optical density value of the cutoff is 3. The thickness of 3.55–3.75 µm bandpass filter was measured and the thickness error was analyzed. The results show that the thickness error, especially the thickness error of spacer layers, induces the degradations of peak transmission and bandwidth. This kind of mid-infrared filter has important application in space remote sensing, military, and civil fields.

Reconfigurable diplexer using hybrid couplers and perturbed TE012 cavities

AbstractA continuously tunable Ku-band waveguide diplexer is proposed in this paper. This diplexer is based on a hybrid coupler topology and is composed of an input filter centered at 11.9 GHz with a 200 MHz bandwidth, a pair of ladder-type hybrid couplers, and a pair of tunable filters. This diplexer can provide two bandpass channels (channels 1 and 2) that can continuously go from a state where the bandwidths of channels 1 and 2 are maximum (up to 140 MHz) and minimum (down to 40 MHz), respectively, to another configuration where the bandwidth of channel 1 is the largest and the bandwidth of channel 2 is the narrowest. We propose a tunable filter based on TE012 mode circular cavities that are perturbed by low-loss dielectric inserts to obtain such performance. The resonant frequency of these cavities can be continuously tuned between 11.8 and 12 GHz due to the linear movement of the dielectric perturber. The design process for these components is presented and a breadboard device has been manufactured and measured to prove the concept. Different measured configurations of the diplexer are demonstrated, showing that the 200 MHz operating bandpass between 11.8 and 12 GHz can be efficiently separated into two tunable channels. The measured bandwidth of channels 1 and 2 in the manufactured diplexer can be tuned from 135 to 40 MHz (and vice versa) while maintaining an average guard band between the channels of approximately 26 ± 7 MHz. The obtained bandwidth tuning ratios are 3.2 for the highest channel and 3.1 for the lowest channel.

A non‐reciprocal bandpass diplexer

This letter presents a non-reciprocal diplexer with integrated functions of a conventional bandpass diplexer and two isolators. This is achieved by spatio-temporally modulating the resonator frequencies in a coupled-resonator diplexer. Due to the high channel-to-channel isolation, the diplexer channels can be independently modulated without affecting each other. A microstrip diplexer example is demonstrated with good agreement between the measurement and the simulation. The fabricated diplexer has two non-reciprocal bandpass channels at 829 and 997 MHz, with a minimal insertion loss of 4.9 and 6.1 dB, and a 20-dB isolation bandwidth of 38 and 37 MHz, respectively. To the best of the authors' knowledge, this is the first time that a non-reciprocal diplexer has been presented.

A Novel 1.7–2.85-GHz Filtering Crossover With Independently Tuned Channel Passbands and Reconfigurable Filtering Power-Dividing Function

In this article, a novel filtering crossover with independently tuned channel passbands and reconfigurable filtering power divider (PD) function based on evanescent-mode cavity (EVA) is proposed for the first time. It consists of four substrate-integrated-waveguide (SIW) EVA resonators loaded with piezoelectric actuators for frequency tuning. Four sets of varactors are used between adjacent resonators for control of interstage coupling, whereas four sets of varactors are inserted between ports and resonators for input-output matching. By controlling resonant frequencies of the EVA resonators and coupling coefficients between adjacent resonators, the passbands of the two orthogonal channels in the filtering crossover can be independently tuned in either synchronous or asynchronous fashion within the frequency range of 1.7-2.81 GHz. Meanwhile, by detuning the resonant frequency of one resonator in the crossover, the proposed structure can be reconfigured to become a three-port filtering PD with continuous frequency tuning covering 1.7-2.85 GHz. Moreover, with the independently tuned feature, a filter with reconfigurable filtering PD and diplexer functions can be easily achieved by attaching the proposed crossover to an external matching junction. Several prototypes were given to demonstrate the proposed techniques. Good agreement is obtained between simulated and measured results.

Design of a Microwave Lowpass – Bandpass Filter using Deep Learning and Artificial Intelligence

In this paper, a lowpass – bandpass dual band microwave filter is designed by using deep learning and artificial intelligence. The designed filter has compact size and desirable pass bands. In the proposed filter, the resonators with Z-shaped and T-shaped lines are used to design the low pass channel, while coupling lines, stepped impedance resonators and open ended stubs are utilized to design the bandpass channel. Artificial neural network (ANN) and deep learning (DL) technique has been utilized to extract the proposed filter transfer function, so the values of the transmission zeros can be located in the desired frequency. This technique can also be used for the other electrical devices. The lowpass channel cut off frequency is 1 GHz, with better than 0.2 dB insertion loss. Also, the bandpass channel main frequency is designed at 2.4 GHz with 0.5 dB insertion loss in the passband.

Design of Microstrip Multifunction Integrated Diplexers With Frequency Division, Frequency Selection, and Power Division Functions

In this study, a novel circuit model was proposed for the design of multifunction integrated diplexers with frequency division, frequency selection, and power division functions. The proposed highly integrated multifunctional diplexer mainly comprises only two different-frequency multimode resonators and two isolation resistors, which results in a compact circuit size. The distributed coupling technique was adopted to integrate the two multimode resonators. One resonator was used to form a channel passband, and the other resonator was used to form another channel passband. Moreover, each channel passband can be independently designed and flexibly allocated. The two resistors loaded between the output feeding lines were introduced to improve the impedance matching of the output ports and the isolation between the output ports for each channel. The coupling structures, theoretical analysis, and design procedure for the proposed multifunction integrated diplexers are described. For demonstration, multifunction integrated diplexers with second-order and third-order filtering responses were designed and fabricated using microstrip technology. The experiment and simulation results were consistent and indicated satisfactory in-band and out-of-band performance.

8fJ/Step Bandpass ADC With Digitally Assisted NTF Re-Configuration

In this work we propose a single channel band-pass (BP) SAR ADC with dynamic noise transfer function (NTF) re-configuration. The proposed ADC employs a low-power two-stage architecture. After the SAR finishes quantization, the residue is extracted by firing the comparator multiple times. An estimate of the residue is obtained by employing a maximum likelihood based estimator (MLE). The output of the ADC is obtained by subtracting a delayed version of the estimated residue from the SAR output thus generating a complex NTF with multiple notches in the spectrum. A 65nm ADC prototype achieves 74.1/78dB SNDR/DR over a 101.2kHz bandwidth while consuming $17~\mu \text{W}$ from a 1V supply at 2.43MS/s. The ADC core occupies an area of 0.12mm2. The ADC achieves 8fJ/c-step bandpass FoM which is $85\times $ better than state-of-the-art BP ADCs with similar bandwidth and $8.7\times $ better than all reported state-of-the-art BP ADCs.

A novel miniaturized microstrip lowpass-bandpass diplexer using patch and interdigital cells for wireless networks

This paper presents a novel design of lowpass-bandpass microstrip diplexer using patch and interdigital cells. In comparison with the previously reported lowpass-bandpass diplexers, the proposed design has the most compact size with the overall area of 0.018 λg2 (351.7 mm2) fabricated on 0.787 mm dielectric substrate height. The lowpass channel has a cut-off frequency (fc) at 1.57 GHz. The resonance frequency of the bandpass channel is located at 3.35 GHz, which is suitable for WiMAX applications. Having low insertion losses at the lowpass and bandpass channels is another feature of this work. For the frequencies above the bandpass channel, the harmonics are attenuated up to 2.8 fc. A theory method is presented to show the behavior of the proposed structure. Finally, the designed diplexer is fabricated and measured, where the simulation results match well with the measurements.