Filter Bandwidth Research Articles

A Wideband If Receiver Chip for Flexibly Scalable mmWave Subarray Combining and Interference Rejection

Large-scale multibeam phased array systems suffer from interbeam interference (IBI) that should be canceled either in the analog or digital domain. In wideband systems such as fifth generation (5G), interference rejection over a wide bandwidth is challenging to achieve, not only due to nonidealities of the receiver chain but also due to the properties of the radio channel. This article presents a scalable IBI cancellation (IBIC) scheme at intermediate frequency (IF) using an IF receiver (IF-RX) chip. The IF-RX provides the flexibility of not just interference rejection between the subarrays but also wideband signal combining over multiple subarrays. It also provides wideband filtering before the analog-to-digital converter (ADC) to support 5G channel bandwidths of up to 800 MHz, high linearity, and low noise figure. A calibration method is proposed to find the cancellation coefficients for the IF-RX in measurements. Furthermore, a simplified over-the-air (OTA) IBIC model for analyzing rejection bandwidth limitations is presented. Interference rejection performance is demonstrated through the OTA measurements using 5G new radio (5G NR) signals. In the OTA measurements, 34–37-dB rejection was achieved for 50–100-MHz signals, while error vector magnitude (EVM) requirements of the 5G standards were met with good margins. Finally, the interference rejection over <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\ttimes 100$</tex-math> </inline-formula> MHz carrier aggregated 5G NR waveform was demonstrated.

Applied Cavity Perturbation Used for Frequency Identification of Channel Ports in Manifold-Coupled Multiplexers

We investigate a practical technique for deembedding the channel filter S-parameters of manifold-coupled multiplexers (MUXs), without detaching filters from the manifold. The method is applicable for MUXs with an arbitrary number of channels and can be used for the device regardless of its bandwidth, guard band, or loss of filters. We reconfigure the N-port MUX to two simpler networks cascaded to each other. We assume that the manifold response is unknown and use the idea of applied perturbation on the channel filter, and then by comparing the response of the overall cascaded network, before and after the perturbation, we approximate the channel port response. The technique is useful in fast detecting the unexpectedly detuned channels or likely faults in the device without unnecessary plugging/unplugging; it is also useful in roughly tuning of the channel filers at the early stage of MUX tuning. The technique can be easily traced by the telecommunication community.

Parameter Justification of a Signal Recognition Algorithm Based on Detection at Two Intermediate Frequencies

Introduction. The signal recognition task for the purposes of RF spectrum management can be solved using a signal recognition algorithm with detection at two intermediate frequencies. This algorithm is based on time–frequency analysis using fast Fourier transform (FFT) and signal envelope processing. Due to the relative simplicity of transformations, this algorithm is implemented on commercially available field programmable gate arrays and allows processing received signals in near real-time. However, the justification of the algorithm parameters providing effective signal recognition by the criterion of minimizing the signal-to-noise ratio (SNR) has not performed so far. Aim. Justification of parameters of the developed signal recognition algorithm, providing the minimum required SNR at the algorithm input. Materials and methods. The efficiency of the developed algorithm was estimated by computer simulation in the MATLAB environment. Results. The influence of the parameters of functional blocks and received signals on the efficiency of the developed algorithm was investigated. For chirp, simple pulse, binary, and quadrature phase shift keying signals, the following parameters are recommended: a pulse duration of 5…20 μs; a chirp rate of 0.8…24 MHz/μs; a code duration of 0.5…1 μs. For these signal parameters, the parameters of the algorithm ensuring its efficiency according to the given criterion are as follows: the number of FFT points equals 1024; the Hamming weight window; bandwidths of band-pass filters are 4 MHz; signal envelope amplitude averaging coefficient equals 0.15…0.25. Conclusion. The algorithm with the scientifically valid parameters can be used for recognition of signals at the input minimum SNR for the given types and parameters of signals.

Study of rib protection devices based on resistant muffler theory for transcostal focused ultrasound therapy

High-intensity focused ultrasound (HIFU) is one of the effective means of treating cancer. One of the current challenges in HIFU treatment is how to minimize thermal damage to the rib during transcostal HIFU treatment and ensure that sufficient energy is delivered to the target area. In this paper, a sound insulation device mounted in front of the rib is proposed to address this challenge. The device is designed based on resistant anechoic theory, combining both reflective and resonant sound energy-blocking mechanisms to enhance the transmission loss and filter bandwidth. The structural parameters of the device are optimized using an orthogonal test method. A finite element method was used to simulate the sound and temperature fields of the sound insulation device with and without different rib spacings. The simulation results demonstrate a significant decrease in sound pressure at the ribs under the protection of the sound insulation device, with no significant difference in sound pressure at the target area. Consequently, the temperature at the ribs decreases, while the temperature at the target area tissue is guaranteed. Furthermore, transcostal HIFU experiments are conducted using real pig ribs and the experimental results validate the accuracy of the simulation results.

L-Band Erbium Fiber Laser with Tunable and Narrow Sub-kHz Linewidth Output

In this paper, a wavelength-selectable erbium-doped fiber (EDF) laser in L-band bandwidth with a simple structure and low cost is described. To obtain stable single-longitudinal-mode (SLM) and narrow laser linewidth, the 2 m unpumped EDF-based saturable absorber (SA) and 100 m single-mode fiber (SMF)-induced Rayleigh backscattering (RB) injection effect are cascaded in the ring cavity of the fiber laser. The EDF SA and feedback RB injection can cause the auto-tracking ultra-narrow bandwidth filter effect to suppress the multiple longitudinal mode oscillations and narrow the laser linewidth. Thus, the tunable SLM wavelength output of the EDF laser with sub-kHz linewidth can be achieved. In the measurement, two EDF ring lasers can be executed when the placement of EDF-based SA and SMF-induced RB are switched to experiment with different output characteristics. The experimental results show that the wavelength bandwidths of the two lasers are between 1558.0 and 1618.0 nm. Additionally, the optimal optical signal-to-noise ratio (OSNR), wavelength linewidth, output power, and stability of the presented EDF laser configuration are also achieved and discussed.

Parallel-coupled bandpass filters with directly coupled input and output resonators

A novel method for modifying input and output coupling in the parallel-coupled bandpass filters, which allows for direct connection of source and load to the outer resonators, is proposed. In the filter modification a coupled-resonator approach is utilized, which allows one for calculating both the impedance of the introduced new quarter-wave section and the necessary coupling modification of the first and second resonators. The proposed filter modification allows for realization of wider bandwidth filters by removing the necessity of narrow gap realization. Further the following gap in the filter is also enhanced, what helps in wide band filter realization. The presented theoretical approach has been confirmed by theoretically calculated responses of three- and seven-resonator filters. The theoretically investigated filter modification has been confirmed with the experiment in which a seven-resonator modified bandpass filter has been fabricated and measured. The presented measurement results confirm the theoretical predictions and prove the proposed design method.

Super-High-Frequency Bulk Acoustic Resonators Based on Aluminum Scandium Nitride for Wideband Applications.

Despite the dominance of bulk acoustic wave (BAW) filters in the high-frequency market due to their superior performance and compatible integration process, the advent of the 5G era brings up new challenges to meet the ever-growing demands on high-frequency and large bandwidth. Al1-xScxN piezoelectric films with high Sc concentration are particularly desirable to achieve an increased electromechanical coupling (Kt2) for BAW resonators and also a larger bandwidth for filters. In this paper, we designed and fabricated the Al1-xScxN-based BAW resonators with Sc concentrations as high as 30%. The symmetry of the resonance region, border frame structure and thickness ratio of the piezoelectric stack are thoroughly examined for lateral modes suppression and resonant performance optimization. Benefiting from the 30% Sc doping, the fabricated BAW resonators demonstrate a large effective electromechanical coupling (Keff2) of 17.8% at 4.75 GHz parallel resonant frequency. Moreover, the temperature coefficient of frequency (TCF) of the device is obtained as -22.9 ppm/°C, indicating reasonable temperature stability. Our results show that BAW resonators based on highly doped Al1-xScxN piezoelectric film have great potential for high-frequency and large bandwidth applications.

Towards a comprehensive model of binaural processing

Most classic models of binaural processing are partly built on assumptions that have been challenged or even contradicted by physiologic or psychoacoustic data. For example, that delay lines encode interaural time difference (ITD), that “binaural filters” are wider than auditory filters, or that the binaural system is sluggish and cannot encode rapidly changing ITDs. While these assumptions have been motivated by psychoacoustic data, they have also been contradicted by other psychoacoustic data. The present study revisits and challenges the respective reasonings. One result is that the psychoacoustic proof of delay lines contained an unmet assumption. Instead of “sometimes wider filters” we propose a spectral incoherence interference mechanism that appears to resolve the impasse of inconsistent filter bandwidth requirements. In the temporal domain, we model fast ITD encoding and binaural sluggishness is realized by slow reformation of the interaural statistics of auditory objects. The resulting model still has some unproven assumptions; however, it does not need to change its parameters depending on the type of stimulus or task. As the binaural filter bandwidths and processing speeds are now equivalent to their monaural counterparts and consistent with physiological findings, the model may be instrumental in moving to a more unified understanding of auditory processing.

Design and performance evaluation of a novel metamaterial broadband THz filter for 6G applications

Terahertz (THz) radiation, which has applications in the imaging of objects, non-destructive testing, satellite communication, medical diagnostics, and biosensing, has generated a great deal of attention due to its remarkable properties. This paper proposes a novel broadband filter for THz applications. The main idea is to overcome the insertion loss and bandwidth issues by modeling a frequency-domain finite difference method and guided-mode resonance (GMR). The optimal design scheme of the wideband pass filter based on the circular resonant ring is discussed by comparing the transmission parameters under various parameters. This scheme overcomes the restriction of the narrow passband bandwidth of the prior THz filters and achieves approximately 3 dB bandwidth of 0.54 THz. The proposed THz filter paper also has the advantages of a straightforward structure, low processing costs, and ease of conformal with other structures, and it can be used for stealth fighters, new communication technology, and precise instruments. In addition, when compared to existing models, the suggested filter offers higher 3 dB BW operation, increased transmittance, low insertion loss, and stable performance at various oblique angles.

Benefits of FIR-based spectral proper orthogonal decomposition in separation of flow dynamics in the wake of a cantilevered square cylinder

A comparative analysis is presented to illustrate the benefits of finite impulse response (FIR)-based spectral proper orthogonal decomposition (SPOD) over traditional proper orthogonal decomposition (POD) in separating coherent contributions within narrow spectral bandwidth. The wake of a cantilevered square cylinder of height-to-width ratio h/d=4 protruding a thin laminar boundary layer (δ/d=0.21) is investigated at a Reynolds number (Re) of 10600 using time-resolved stereoscopic particle image velocimetry. In the vicinity of the obstacle-plate junction region (z<0.5d), spectral analysis of the temporal modes obtained with both POD and FIR-based SPOD show fluctuation energy concentration centered on the vortex shedding frequency (fs), as well as weaker contributions at 0.1, 0.4, 0.9, 0.95, 1.05, 1.1, and 2fs. Broad-band spectral energy concentrations around 0.4fs are mainly observed close to the ground plane, while the energy contents at (1±0.05)fs and (1±0.1)fs increase at higher planes. With POD, the frequencies are not separated in the modes and it is very difficult to associate each to specific phenomena within the wake region. However, with tuning of the filter bandwidth, FIR-based SPOD represents each of the identified frequencies in a separate mode pair, which permits a better interpretation of the related dynamics. Notably, the improved modal separation assists in associating the 0.4fs spectral contribution with the interactions between the extensions of horseshoe vortex system and Kármán vortices in the wall-body junction region and the (1±0.05)fs and (1±0.1)fs frequencies to perturbation of the shedding cycle resulting from interactions with the lower frequency dynamics.

Virtual inertia analysis of photovoltaic energy storage systems based on reduced-order model

The problem of non-ideal inertia of the photovoltaic energy storage system (PVESS) may occur due to unreasonable voltage control parameters. In response to this issue, this paper establishes an equivalent reduced-order model (EROM) for PVESS. This EROM considers the current control loop, voltage control loop and the virtual inertia control loop based on low-pass filter. This low-pass filter can effectively enhance the system’s virtual inertia. Since the output impedance of this EROM can visually reflect the external characteristics of the virtual inertia control loop, it is suitable for inertia analysis of PVESS. Furthermore, the impact of voltage control parameters and low-pass filter bandwidth on the system’s inertia is discussed from the perspective of the frequency response of the output impedance. Finally, the switch model of the PVESS is built on the RT-BOX hardware-in-the-loop experimental platform. The validity of the EROM and theoretical analysis is verified by several sets of experimental results.

Electroluminescence hyperspectral imaging of light-emitting diodes using a liquid crystal tunable filter

We demonstrate the use of a low-cost liquid-crystal-based wavelength-tunable filter and CMOS video camera to add hyperspectral imaging capabilities to a probe station equipped with a simple optical microscope. The resultant setup is used to rapidly resolve the spectral and spatial variations in electroluminescence typically observed for InxGa1−xN/GaN light-emitting diodes. Applying standard statistical analyses of variation within the multivariate datasets, such as moments and principal components, we observe inhomogeneities on a spectral scale significantly smaller than the bandwidth of the tunable filter. The resultant tool offers an alternative to scanning beam luminescence techniques for high-throughput hyperspectral analysis of optoelectronic devices.

Limits of the spatial ventricular gradient and QRST angles in patients with normal electrocardiograms and no known cardiovascular disease stratified by age, sex, and race.

Measurement of the spatial ventricular gradient (SVG), spatial QRST angles, and other vectorcardiographic measures of myocardial electrical heterogeneity have emerged as novel risk stratification methods for sudden cardiac death and other adverse cardiovascular events. Prior studies of normal limits of these measurements included primarily young, healthy, White volunteers, but normal limits in older patients are unknown. The influence of race and body mass index (BMI) on these measurements is also unclear. Normal 12-lead electrocardiograms (ECGs) from a single center were identified. Patients with abnormal cardiovascular, pulmonary, or renal history (assessed by International Classification of Disease[ICD-9/ICD-10] codes)or abnormal cardiovascular imaging were excluded. The SVG and QRST angles were measured and stratified by age, sex, and race. Multivariable linear regression was used to assess the influence of age, BMI, and heart rate (HR) on these measurements. Among 3292 patients, observed ranges of SVG and QRST angles (peak and mean) differed significantly based on sex, age, and race. Sex differences attenuated with increasing age. Men tended to have larger SVG magnitude (60.4 [46.1-77.8] vs. 52.5 [41.3-65.8] mv*ms, p < .0001) and elevation, and more anterior/negative SVG azimuth (-14.8 [-25.1 to -4.3] vs. 1.3 [-9.8 to 10.5] deg, p < .0001) compared to women. Men also had wider QRST angles. Observed ranges varied significantly with BMI and HR. SVG and QRST angle measurements were robust to different filtering bandwidths and moderate fiducial point annotation errors, but were heavily affected by changes in baseline correction. Age, sex, race, BMI, and HR significantly affect the range of SVG and QRST angles in patients with normal ECGs and no known cardiovascular disease, and should be accounted for in future studies. An online calculator for prediction of these "normal limits" given demographics is provided at https://bivectors.github.io/gehcalc/.

Nucleation control of high crystal quality heteroepitaxial Sc0.4Al0.6N grown by molecular beam epitaxy

High ScN fraction ScxAl1−xN has promise in important application areas including wide bandwidth RF resonators and filters, and ferroelectric devices such as non-volatile memory, but demands high crystal quality. In this work, the role of the nucleation layer (NL), ScxAl1−xN growth temperature, and strain management to preserve the wurtzite crystal structure are investigated to maximize both acoustoelectric and ferroelectric material properties for high ScN fraction ScxAl1−xN grown on SiC substrates. A 5 nm AlN nucleation layer reduces the x-ray diffraction 0002 reflection full width at half maximum (FWHM) for a Sc0.32Al0.68N film by almost a factor of 2, and reducing the growth temperature to 430 °C enables a Sc0.40Al0.60N film with a FWHM of 4100 arcsec (1.1°) while being only 150 nm thick. Grading the initial ScxAl1−xN layer from x = 0.32 to 0.40 suppresses the formation of rock-salt grain nucleation at the Sc0.40Al0.60N lower interface and reduces the anomalously oriented grain density by an order of magnitude. Increasing the total ScxAl1−xN growth thickness to 500 nm produces an average x = 0.39 ScxAl1−xN layer with a FWHM of 3190 arcsec (0.89°) and an anomalously oriented grain areal fill factor of 1.0%. These methods enable the lowest heteroepitaxial ScxAl1−xN FWHM reported for x ∼ 0.4, with layer thicknesses and defect densities appropriate for high frequency (&amp;gt;10 GHz) filter applications.

Partially Etched Piezoelectric Film Filled with SiO2 Structure Applied to A1 Mode Resonators for Transverse Modes Suppression.

With the arrival of the Fifth Generation (5G) communication era, there has been an urgent demand for acoustic filters with a high frequency and ultrawide bandwidth used in radio-frequency (RF) front-ends filtering and signal processing. First-order antisymmetric (A1) lamb mode resonators based on LiNbO3 film have attracted wide attention due to their scalable, high operating frequency and large electromechanical coupling coefficients (K2), making them promising candidates for sub-6 GHz wideband filters. However, A1 mode resonators suffer from the occurrence of transverse modes, which should be addressed to make these devices suitable for applications. In this work, theoretical analysis is performed by finite element method (FEM), and the admittance characteristics of an A1 mode resonator and displacement of transverse modes near the resonant frequency (fr) are investigated. We propose a novel Dielectric-Embedded Piston Mode (DEPM) structure, achieved by partially etching a piezoelectric film filled with SiO2, which can almost suppress the transverse modes between the resonant frequency (fr) and anti-resonant frequency (fa) when applied on ZY-cut LiNbO3-based A1 mode resonators. This indicates that compared with Broadband Piston Mode (BPM), Filled-broadband Piston Mode (FPM) and standard structures, the DEPM structure is superior. Furthermore, the design parameters of the resonator are optimized by adjusting the width, depth and filled materials in the etched window of the DEPM structure to obtain a better suppression of transverse modes. The optimized A1 mode resonator using a DEPM structure exhibits a transverse-free response with a high fr of 3.22 GHz and a large K2 of ~30%, which promotes the application of A1 mode devices for use in 5G RF front-ends.

Space–time-range clutter suppression via tensor-based STAP for airborne FDA-MIMO radar

Frequency diverse array (FDA) multiple-input multiple-out (MIMO) radar has an inherent higher-dimensional data structure that can be exploited in temporal, spatial, and range-dependent dimensions for space–time-range adaptive processing (STRAP). This paper addresses the problem of tensor filters in application to space–time-range clutter suppression for FDA-MIMO radar. The characteristics of space–time-range clutter are discussed to establish the multidimensional signal models. FDA-MIMO radar can divide the secondary range cell within the range resolution cell of MIMO radar when they have the same matching filter bandwidth in the receive channel. Specifically, the target-free covariance information can be estimated from more secondary training cells for FDA-MIMO radar. According to the discussed properties of space–time-range clutter, namely secondary clutter rings, clutter degrees of freedom (DOFs), and the range-dimensional non-stationary characteristic, a tensor-based STRAP approach with range compensation is proposed to suppress clutter for FDA-MIMO radar. Numerical results verify the mentioned clutter characteristics and illustrate the importance of the samples number and range compensation operation for the proposed tensor filter. Finally, the STRAP performance benefits of FDA-MIMO radar over MIMO radar are discussed by simulations.

Virtual Admittance Feedforward Compensation and Phase Correction for Average-Current-Mode-Controlled Totem-Pole PFC Converters

This paper explores a current distortion problem in totem-pole bridgeless power factor correction (PFC) converters with average current mode (ACM) control. With in-depth modeling for the current and voltage loops, it was found that the current distortion is caused by the limited current loop bandwidth and input filter capacitor. These factors lead to the presence of a susceptance component in the input admittance, which degrades the power factor (PF) and total harmonic distortion (THD) of the PFC converter. To solve this problem, this paper proposes virtual admittance feedforward compensation (VAFC) and phase correction methods to adjust the input admittance to pure conductance. The VAFC can generate virtual admittance that compensates for susceptance components in the input admittance, while phase correction can generate an equivalent current source that offsets the current in input capacitors. Furthermore, a phase lock loop (PLL) is introduced to realize the VAFC, which reduces the feedforward interference caused by input voltage sampling noise. Finally, an experimental prototype was built to verify the effectiveness of the proposed strategies. According to the test results, the proposed compensation strategy improves the PF by 1.23%, while reducing the THD by 2.52% and achieving a peak efficiency of 98.69%.

Design and analysis of tunable optical filter based on silicon-on-insulator photonic crystal for visible light communication

In this paper, tunable narrow bandwidth band-stop and band-pass optical filters for visible light communication (VLC) are designed and numerically investigated using a photonic crystal (PC) structure. Designing a tunable filter for visible light communication is crucial for enhancing spectral utilization and maximizing communication efficiency. A rectangular defect with optimized sides length utilized in the center of the PC structure based on the desired filtering characteristics. To obtain a favorable narrow bandwidth filter for visible light wavelengths, this defect is filled with a specific liquid crystal. In addition, an electric field is applied to the proposed structure in order to change the refractive index of the liquid crystal and achieve tunability in the desired range. The functional wavelength ranges of band-pass and band-stop filters are 550–570 nm and 565–585 nm, respectively. Applying an electric field causes a shift in the central wavelengths of the filters. It is shown that a 1.5 nm central wavelength shift for a band-stop filter and a 0.9 nm central wavelength shift for a band-pass filter can be achieved by changing the voltage source up to 1.5 V. In addition, the impact that the variation in the length of the rectangular defects’ sides has on the filtering characteristics of the proposed device is studied.

Improving the Accuracy and Resolution of Filter- and Frequency-to-Time Mapping-Based Time and Frequency Acquisition Methods by Broadening the Filter Bandwidth

In this article, a method for improving the accuracy and resolution of the filter-and frequency-to-time mapping (FTTM)-based time and frequency acquisition system in the fast sweep scenario is proposed by broadening the filter bandwidth. It is found that the width of the generated pulse via FTTM is mainly determined by the impulse response of the filter when the sweep rate is very fast. Therefore, appropriately increasing the filter bandwidth can significantly reduce the pulsewidth, so as to improve the measurement accuracy and resolution. To verify the validity, short-time Fourier transform (STFT) and microwave frequency measurement (MFM) systems employing the stimulated Brillouin scattering (SBS)-based FTTM are further investigated by inserting a frequency-sweep pump wave for SBS gain bandwidth broadening. The improvement of accuracy and frequency resolution is well confirmed by comparing the measurement results with and without SBS gain spectrum broadening. The MFM accuracy is improved by more than ten times compared with other reported works under a similar fast sweep rate, and the frequency resolution of the STFT is also much improved compared with our former results.

Toward Band n78 Shear Bulk Acoustic Resonators Using Crystalline Y-Cut Lithium Niobate Films With Spurious Suppression

This work presents the study of suspended Y-cut Lithium Niobate shear bulk acoustic resonators for wide band filter applications in the frequency range of 3.5-4.5GHz. The resonators consist of a Lithium Niobate film with Aluminum top interdigitated electrodes (IDE) and floating bottom metal plate. Through vertical electric field excitation, shear bulk acoustic waves are generated in each unit cell of the device functioning as a quasi-independent resonator. Measured devices at 3.7GHz having large relative resonance-antiresonance bandwidth of 16.7% (750MHz), with 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{\Omega }$</tex-math> </inline-formula> impedance at resonance are presented. Suppression of higher order lateral harmonics through etching of trenches in the Lithium Niobate and geometric optimization is discussed.2022-0205