Rejection Bandwidth Research Articles

Compact high attenuation wide rejection bandwidth 5-pole Butterworth LPF using transmission zeros in GaAs process

In this work, a systematic design method for a compact 5-pole Butterworth transverse resonance low pass filter (TR-LPF), in 0.15 μm Gallium Arsenide process, with wide rejection bandwidth (RBW), is presented. The circuit model of TR-LPF and closed-form expressions are provided to appreciate the design process. The fabricated TR-LPF has a cut-off frequency of 10.5 GHz, an insertion loss of 0.4 dB, and the return loss is better than 20 dB. The 20 dB, 30 dB, and 40 dB deep rejection bandwidths (RBWs), across 50 GHz, 45.5 GHz, and 17 GHz respectively, are obtained. The novel use of stubs and spur resonators, within stubs; provides the deep and wide RBW. The compactness of the TR-LPF is realized by the ‘C’-and ‘Z’-shaped folding of stubs. The dimension of the filter is approximately 0.11λg×0.079λg.

Sidewall Corrugation-Modulated Phase-Apodized Silicon Grating Filter.

In this work, phase-apodized silicon grating filters with varying sidewall corrugation width and location were investigated, while the resonance wavelength, extinction ratio, and rejection bandwidth were tuned flexibly. The grating filters with a waveguide width of 500 nm and grating period of 400 nm were fabricated and characterized as a proof of concept. The resonance wavelength of the device can be shifted by 4.54 nm by varying the sidewall corrugation width from 150 to 250 nm. The corresponding rejection bandwidth can be changed from 1.19 to 2.03 nm by applying a sidewall corrugation location offset from 50 to 200 nm. The experimental performances coincide well with the simulation results. The presented sidewall corrugation-modulated apodized grating can be expected to have great application prospects for optical communications and semiconductor lasers.

Design of Miniaturized 90-Degree Hybrid Coupler with Wide Rejection Band Using Neural Network.

In this paper, a 3 dB 90-degree hybrid coupler with size reduction and harmonics rejection was designed. In the proposed coupler structure, four simple low-pass filters (LPFs) were applied. An artificial neural network (ANN) was used to determine the dimensions of the applied LPFs based on EM simulation data. The applied ANN model could also provide the desired LPF parameters, including the cut-off frequency (fc), bandwidth (BW), and insertion loss (IL). Designing an applied LPF involves complex mathematical calculations and simulations to optimize parameters. However, by utilizing neural networks, the design process can be significantly streamlined and automated. Neural networks have the ability to learn complex patterns and relationships within data, making them well suited for optimizing the performance of applied components. The proposed 90-degree hybrid coupler works correctly at 1800 MHz and has a small size of 16.6 mm × 15.15 mm, which provides a 73% size reduction compared to a normal 1800 MHz coupler. The designed coupler not only decreases the circuit size but also provides a wide rejection band from 4.8 GHz to 11.2 GHz, which suppresses the second to sixth harmonics. The insertion loss parameter of this 90-degree hybrid coupler is less than 0.1 dB at the working frequency, which shows the superior performance of the proposed coupler.

On-chip ultra-high rejection and narrow bandwidth filter based on coherency-broken cascaded cladding-modulated gratings

Bragg filters are of essential importance for chip-scale photonic systems. However, the implementation of filters with sub-nanometer bandwidth and rejection beyond 70 dB is hindered by the high index contrast of the silicon-on-insulator platform, which makes filters prone to fabrication imperfections. In this paper, we propose to combine coherency-broken cascading architecture and cladding modulation to circumvent the intrinsic limitation. The cascading architecture effectively prevents the accumulation of phase errors, while the cladding modulation offers additional design freedom to reduce the coupling coefficient. A bimodal Bragg filter with a testing-equipment-limited rejection level of 74 dB and a 40 dB bandwidth of 0.44 nm is experimentally demonstrated. The minimum feature size is 90 nm, which significantly relieves the fabrication constraints.

A Multifunctionality Reconfigurable HMSIW Filter by Using EBG Structure and Diodes for C/X-Band Application

This letter presents a multifunctionality reconfigurable substrate-integrated waveguide (SIW) filter embedded in a microstrip line. The proposed filter used an electromagnetic bandgap structure (EBG) to compact the size and improve the electromagnetic features. The SIW filter consists of a three-cell EBG with metallic circular-shaped connected to the ground through cylindrical vias. Firstly, the base SIW structure offers a wide passband filtering response, and then, to obtain selective passband, wide band rejection, and controllable resonance frequencies, a three-cell EBG along with four diodes has been attached. The filter is designed and printed on a Rogers 4003 substrate with a thickness of 1 mm and is experimentally validated for functionalities operated at three modes with an average 3 dB bandwidth of 115 MHz in each frequency. In addition to that, two transmission zeros (TZ) have been produced in the upper band frequency. The filter’s response is also tunable by turning the diode off or on and changing the main parameters of EBG, the gab, and the position between cells. The study explores resonance frequency alterations in a three-state system of on/off. By eliminating or diminishing specific modes, and incorporating diodes, distinct resonance behaviors are observed. Moreover, shifting frequency resonance in a multiparameter system has been investigated. Increasing B1 induces a significant shift to lower values, while an increase in D1 leads to a decrease in the first and second resonance frequencies and an upward shift in the third. The designed filter has been fabricated and tested to compare and confirm simulated responses. Simulation and measurement results are in good agreement. The S-parameters of measured results gained a good response (>15 dB) within the passbands and stopbands and an insertion loss of 1.5 dB suitable for 5G and Wi-Fi systems.

Switchable and optically transparent ultrawide stopband frequency selective surface for electromagnetic shielding

In view of the fact that high-frequency electromagnetic waves mainly enter buildings through windows and glass doors, switchable optically-transparent shielding with broad stopband is increasingly needed. Herein, a novel design for a switchable and optically transparent frequency selective surface (FSS) with ultrawide-stopband is presented in this study. The structure consists of a polymethyl methacrylate (PMMA) layer sandwiched between polydimethylsiloxane (PDMS) layers which contain liquid metal microchannels arranged in an orthogonal Ω-shaped configuration. The mobility of the liquid metal can switch the FSS response from an all-pass to an ultrawide bandstop behavior. The proposed FSS achieves a rejection bandwidth of 18.1 GHz, covering P, L, S, C, X and Ku bands, while maintaining a transparency of 81% and high angular stability up to 80°, regardless of polarization. Furthermore, the mechanism behind the ultrawide stopband and high angular stability is explored through an analysis of reflection and absorption for both TE polarization and TM polarization. Experimental validation under both normal and oblique incidence demonstrates the ultrawide-stopband performance of the fabricated FSS.

A Miniaturized Bandpass Filter with Wideband and High Stopband Rejection Using LTCC Technology

This paper designs an L-band wide stopband bandpass filter by applying low-temperature cofired ceramic (LTCC) technology to the global positioning system (GPS) frequency band. Taking the Chebyshev filter as a prototype, an equivalent collector element (capacitive and inductor) structure is adopted to fully use the three-dimensional package structure of LTCC to reduce the filter size. The filter is integrated into an eight-layer LTCC dielectric, and the series–parallel connection of the collector elements in the resonance unit is utilized to produce out-of-band transmission zeros, while the input and output ports’ capacitance is adjusted to control the bandwidth. Harmonic suppression is achieved by cascading two new compact stopband filters, while the size increase is insignificant due to LTCC technology. The simulation results are as follows: the center frequency is 1.575 GHz, 1 dB relative bandwidth is 6.3%, insertion loss in the passband is as slight as 1.6 dB, return loss is better than 30 dB, rejection bandwidth up to 16 GHz is more than 44 dB, and the volume of the whole filter is 6.2 × 3.7 × 0.78 mm3.

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.

Offset Voltage Reduction in Two-Stage Folded-Cascode Operational Amplifier Using High-Precision Source Degeneration

The demand for CMOS precision operational amplifiers for critical applications has continuously increased over time due to higher accuracy and sensitivity requirements. Trimming or chopper architectures are advanced solutions that reduce the offset voltage and improve the circuit’s parameters, but the complexity and the increased chip die size are serious downsides. An efficient solution is a source degeneration configuration to control the transistor’s current-mirror transconductance, which impacts the offset voltage, with cost savings and a die area reduction also obtained. This paper focuses on designing and implementing such an approach in a two-stage folded-cascode operational amplifier. State-of-the-art thin-film resistors that use silicon–chromium as the metallic alloy were implemented to reduce mismatch variations between these passive components. Distinct methods that control the offset voltage parameter are also discussed and established. A comparison between the offset voltage standard deviation obtained using different types of resistors and that achieved with the innovative high-precision resistors was also carried out. The source degeneration’s impact on the common-mode rejection ratio, power supply rejection ratio, bandwidth and phase margin was also analyzed, and a comparison between the proposed design and the classical one was performed. The process variation’s influence on the circuit functionality was studied. A pre-layout ±1.273 mV maximum offset voltage at T = 27 °C was achieved using vector/array notations for the amplifier with the best overall performance. Post-layout simulations that included parasitic effects were performed, with a ±1.254 mV maximum offset voltage reached at room temperature.

Design of single‐layer bandstop fractal frequency selective surface based on WLAN applications

AbstractIn this letter, we present a new frequency selective surface (FSS) for shielding 2.4–2.5 and 4.98–5.825 GHz wireless local area network (WLAN) bands. This FSS structure is based on the traditional Sierpinski octagon and we improve it. Compared with the traditional structure, the improved one has a smaller element size and better angular stability. The design is realized on float glass with a relative permittivity () of 8, and the unit cell size is 0.1152λ0 × 0.1152λ0 (λ0 is the free space wavelength at the first resonant frequency). Wide rejection bandwidths (−10 dB) of 910 and 1630 MHz are obtained at 2.4–2.5 and 4.98–5.825 GHz, respectively. The surface current distribution and the equivalent circuit model are illustrated to explain the resonance behavior of the proposed FSS. Furthermore, this FSS exhibits stable frequency response to incident angles of 0°–80° under transverse electric and transverse magnetic polarizations. Finally, this FSS structure was fabricated and measured. The measured results demonstrate that this FSS structure has good performance in WLAN applications.

Discrete-Time Frequency-Domain Disturbance Observer to Mitigate Harmonic Current in PMSM Drives and the Implementation With Reduced Delay

The disturbance observer (DOB) can be employed in electric drives to improve disturbance rejection. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -filter of classical frequency-domain DOBs to attenuate multiple harmonic disturbances is high-order and faces issues including discretization, numerical precision, and frequency adaption, thus its realization in variable-speed drives would be challengeable. This paper proposes a discrete-time multi-frequency DOB (MFDOB) to address these issues. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -filter of the proposed design is constructed with an integrator and several parallel resonators in a closed-loop structure. It uses a single parameter per harmonic to control the disturbance rejection bandwidth and the performance is guaranteed under various fundamental frequencies. The impact of the computation delay on the MFDOB-based current control is studied, and the system with less computation delay exhibits a higher stability margin and a wider range of low sensitivity. To eliminate the computation delay, a real-time pulse-width-modulation (PWM) update scheme is also developed for the DOB-based two-degree-of-freedom (2DOF) controller. The proposed method is evaluated on a laboratory permanent magnet synchronous machine platform.

Femtosecond laser fabrication of chirped and tilted fiber Bragg gratings for stimulated Raman scattering suppression in kilowatt-level fiber lasers.

Chirped and tilted fiber Bragg gratings (CTFBGs) are important all-fiber filtering components in high-power fiber lasers for stimulated Raman scattering (SRS) suppression. The fabrication of CTFBGs in large-mode-area double-cladding fibers (LMA-DCFs) by femtosecond (fs) laser is reported for the first time to the best of our knowledge. The chirped and tilted grating structure is obtained by scanning the fiber obliquely and moving the fs-laser beam relative to the chirped phase mask at the same time. By this method, the CTFBGs with different chirp rates, grating lengths, and tilted angles are fabricated, and the maximum rejection depth and bandwidth are ∼25 dB and ∼12 nm, respectively. To test the performance of the fabricated CTFBGs, one is inserted between the seed laser and the amplifier stage of a 2.7 kW fiber amplifier, and an SRS suppression ratio of ∼4 dB is achieved with no reduction in laser efficiency and degradation in beam quality. This work provides a highly fast and flexible method to fabricate large-core CTFBGs, which is of great significance to the development of high-power fiber laser systems.

Packaged Filtering Power Divider With High Selectivity, Extended Stopband and Wideband Isolation

A packaged filtering power divider (FPD) is presented, investigated and synthesized. The radiation loss and electromagnetic interference are reduced since the FPD is insulated in a completely enclosed substrate-integrated cavity. The isolation performance and transmission property of the proposed FPD are determined by the odd- and even-mode equivalent circuit, respectively. A 3rd-order quasi-elliptic filtering response is attained by the multi-mode filtering sections composed of doubly-stub-loaded parallel-coupled lines. Five extra TZs are generated by both the central-loading (CL) T-shaped stub and side-loading (SL) short-circuited 180° and open-circuited 90° branches, which further improves the selectivity of the passband and suppresses the higher-order harmonics. Two isolation resistors are elaborately placed between the two power-division paths, which significantly improves the isolation level over the whole passband and stopband. The design equations including the position of the TPs and TZs, and the values of the isolation resistors are derived in the synthesis procedure. For verification, an FPD prototype is designed, simulated, and measured. It exhibits advantages in terms of low loss, sharp band-edge skirts as well as wideband rejection and isolation, which is suitable for IoT (Internet of Things) applications and antenna-array feeding networks.

Bandpass Filter With Reconfigurable Rejection and Deep-Upper-Wideband Harmonics Suppression Using Spoof Surface Plasmon Polaritons of Hollowed-Bow-Tie Cells

A bandpass filter with a reconfigurable rejection is designed and experimentally validated by exploiting spoof surface plasmon polaritons (SPPs) of hollowed-bow-tie (HBT) cells. As a novel structural discovery, the dispersion curve of the proposed C-loaded HBT cell splits into two modes comparing with the traditional bow-tie cell. With properties of propagating on metal–dielectric interfaces and the exponential increasing propagation constant, SPPs waves show advantages of low crosstalk and tightly confined fields, and experimental results verify that the harmonics suppression level of the transmission characteristic is above 20 dB from 6 to 16 GHz. Moreover, integrated with lumped elements, direct current (dc) bias circuits, and varactor diodes, the designed bandpass filter also has a low cutoff frequency and a reconfigurable rejection. By regulating the bias voltage, the rejection level, frequency, and bandwidth of the stopband are tuned accordingly. The cell dispersion relationships, equivalent circuits, and the near-field distribution are given for theory analyses, and all the full-wave simulations validate well with measurements. The proposed bandpass filter lays a ramming foundation for complex reconfigurable integrated microwave systems, electronically controlled antenna feed networks, and adjustable anti-interference systems.

On Controlling the Passband and Stopband of UWB Band-Pass Filter

In this article, the passband, and stopband of quarter wavelength stubs-based Band Pass Filter (BPF) are controlled by a straightforward and new method. This method depends on inserting an attenuation pole and tuning the passband by a Circular Slot Ring Resonator (CSRR) and rectangular slot beneath the BPF’s stubs. Hence, controlling the passband width without any further area usage is achieved. The stop-band rejection level and bandwidth are controlled by inserting Band Stop Filter (BSF) after the BPF such that the used rectangular slots beneath the stubs control the stop-band bandwidth. For verification, third-order Chebyshev BPF and Butterworth BSF filters are used. The proposed filter passband is chosen to cover the sub-6 GHz different 5G bands. The proposed BPF has an ultra-wide 3 dB passband of 2.97 GHz (2.35 GHz-5.32 GHz) and a 20 dB stopband of 4.59 GHz (6.18-10.77 GHz). The proposed BPF filter is fabricated, measured, and the results are in good agreement with their simulated counterparts.

Implementation of High-Q Embedded Band Pass Filter in Wireless Communication

At 12.8 MHz center frequency, the advanced miniaturized polymer-based planar high quality factor (Q) passive elements embedded bandpass filter works in the L-band. Because most of the demands operate inside the spectrum, the wideband or high-speed operation necessary to enhance must be acquired in microwave frequency ranges. The channel has a quiet, high-performance microfilter with wideband rejection. Capacitors and inductors are used in the high quality factor (Q) passive components, and related networks are incorporated in the filter. Embedded layers are concatenated using Three-Dimensional Integrated Circuit (3D-IC) integration, parasitics are removed, and interconnection losses are negotiated using de-embedding methods. A wireless application-based Liquid Crystalline Polymer (LCP) viewpoint is employed as a substrate material in this work. The polymer processes, their properties, and the incorporated high-Q Band Pass Filter Framework. The suggested filter model is computed and manufactured utilizing the L-band frequency spectrum, decreasing total physical length by 31% while increasing bandwidth by 45%.

Collinear opto-optical loss modulation for carrier-envelope offset stabilization of a fiber frequency comb.

Opto-optical loss modulation (OOM) for stabilization of the carrier-envelope offset (CEO) frequency of a femtosecond all-fiber laser is performed using a collinear geometry. Amplitude-modulated 1064 nm light is fiber coupled into an end-pumped semiconductor saturable absorber mirror (SESAM)-mode-locked all-polarization-maintaining erbium fiber femtosecond laser, where it optically modulates the loss of the SESAM resulting in modulation of the CEO frequency. A noise rejection bandwidth of 150 kHz is achieved when OOM and optical gain modulation are combined in a hybrid analog/digital loop. Collinear OOM provides a simple, all-fiber, high-bandwidth method for improving the CEO frequency stability of SESAM mode-locked fiber lasers.

Active Control of Highly Autocorrelated Machinery Noise in Multivariate Nonminimum Phase Systems

In this paper, a novel multivariate active noise control scheme, designed to attenuate disturbances with high autocorrelation characteristics and preserve background signals, is proposed. The algorithm belongs to the class of feedback controllers and, unlike the popular feedforward FX-LMS approach, does not require availability of a reference signal. The proposed approach draws its inspiration from the iterative learning control and repetitive mode control methods, and employs a modified inverse model learning law. The classical inverse model learning law is well known to offer fast convergence and high steady-state performance, provided that the secondary path is minimum phase and well known. The proposed modified inverse model learning law employs a spectral factorization trick, which allows one to use the method with nonminimum phase plants of arbitrary order. Moreover, our scheme includes a controller bandwidth limiting mechanism that can be used to tune the disturbance rejection bandwidth and to improve the closed-loop robustness to errors in the model of the secondary path. The algorithm’s behavior and performance are verified with computer simulations that demonstrate suppression of electrical transformer noise and include realistic models of the secondary path. The results show high-level selective attenuation and fast convergence.

Design of high‐efficiency , multi‐octave hybrid continuous mode power amplifier with novel low‐pass filtering matching network

This paper presents a design method for a multi-octave, high-efficiency power amplifier (PA) with a novel low-pass filtering matching network. Both extended continuous Class-F and continuous Class-F−1 are engaged to expand the design space for the ultra-broad operating band. A wideband vertex coupled radial stubs (VCRS) low-pass filter alongside a transmission line network (TLN) is proposed as an output impedance matching network of the PA. The wide rejection band and sharp transition band of this filter make it suitable for harmonic tuning PAs. To verify the feasibility of the proposed structure, the PA is fabricated and its performance is measured. The fractional bandwidth of 155% across 150 to 1200 MHz with a drain efficiency of 61%–73% and output power of 38.9–39.5 dBm is achieved.

Sinusoidal and rectangular Bragg grating filters: Design, fabrication, and comparative analysis

In this paper, we compare the characteristics of several waveguide Bragg gratings (WBGs) with sinusoidal and rectangular corrugated sidewalls in high confinement integrated optics. Our measurements confirm the performance of both the rectangular and sinusoidal grating as band-rejection filters for TE-polarized signals in the telecom C-band. These measurements demonstrate record high extinction ratios of 35 and 28.91 dB for sinusoidal and rectangular WBGs with a rejection bandwidth as narrow as 4.42 and 6.165 nm. The simulation results and measurements show that the filter bandwidth and coupling coefficient can be changed by altering the corrugation width (ΔW), allowing us to control the filter’s quality factor precisely. The bandwidth of rectangular WBGs drops for ΔW&amp;gt;80 nm, constraining the design of devices requiring broadband WBGs. In contrast, the bandwidth of sinusoidal WBG continues to increase for ΔW&amp;gt;80 nm, providing a wider bandwidth for designers. These findings demonstrate the potential for effective integration of new photonic functionalities into low-footprint electro-optical waveguide tools for sensing, communicating, and computing applications.