High Stopband Research Articles

On design of preprocessing and postprocessing in cascaded-resonator-based harmonic analyzers and filter banks

The cascaded-resonator (CR)-based filter structure provides high attenuation in the stopbands thanks to the serially coupled resonators, which is an advantage in many applications of harmonic analyses and/or filtering. In addition to that, it has good properties provided by its parallel structure. On the other side, there are applications which besides the high stopband attenuation need wider (or even flat-top) passbands, lower group delays, etc. These performances can be modified/improved by preprocessing and postprocessing through reshaping of the primary CR-based filter bank frequency responses. The numerical complexity is also an important aspect where infinite impulse response (IIR) filters provide implementation with a smaller number of numerical operations, but involving nonlinearity of the phase responses and stability control issue. Although most of these issues have been discussed in the previous papers dealing with the design of the CR-based harmonic filtering and/or filter banks, the aim of this paper is to highlight them all together. In addition, some improvements of the previously described design techniques are suggested too.

Design and Miniaturized a High Suppression Stop band Micro strip Low Pass Filter by using Slot Defected Ground Structure for 5G Applications

Design and Miniaturized a High Suppression Stop band Micro strip Low Pass Filter by using Slot Defected Ground Structure for 5G Applications

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.

Wideband and Highly Selective BandPass Filter Using Substrate Integrated Waveguide Technology for Ku-Band Applications

A new compact design of bandpass filter using substrate integrated waveguide (SIW) is proposed and analyzed in this paper. It offers good in-band return loss, low insertion loss, wide passband, and high stopband attenuation. The filtering response is achieved by loading a couple of inverted tuning fork-shaped defected ground structures (DGS) on the bottom of the SIW cavity. DGS is utilized to enhance the upper stopband performance. To validate, the filter is fabricated using Rogers RT/Duroid 5880 with 0.508 mm thickness and tested. The filter has a center frequency of 15.44 GHz with 19% fractional bandwidth (FBW). The return loss is more than 20 dB and the insertion loss is about 1.2 dB. It finds its application in Ku band satellite communication.

Metamaterial inspired electromagnetic bandgap filter for ultra-wide stopband screening devices of electromagnetic interference

Presented here is a reactively loaded microstrip transmission line that exhibit an ultra-wide bandgap. The reactive loading is periodically distributed along the transmission line, which is electromagnetically coupled. The reactive load consists of a circular shaped patch which is converted to a metamaterial structure by embedded on it two concentric slit-rings. The patch is connected to the ground plane with a via-hole. The resulting structure exhibits electromagnetic bandgap (EBG) properties. The size and gap between the slit-rings dictate the magnitude of the reactive loading. The structure was first theoretically modelled to gain insight of the characterizing parameters. The equivalent circuit was verified using a full-wave 3D electromagnetic (EM) solver. The measured results show the proposed EBG structure has a highly sharp 3-dB skirt and a very wide bandgap, which is substantially larger than any EBG structure reported to date. The bandgap rejection of the single EBG unit-cell is better than − 30 dB, and the five element EBG unit-cell is better than − 90 dB. The innovation can be used in various applications such as biomedical applications that are requiring sharp roll-off rates and high stopband rejection thus enabling efficient use of the EM spectrum. This can reduce guard band and thereby increase the channel capacity of wireless systems.

A Single-Layer Wideband Differential-Fed Filtering Antenna With High Selectivity

In this communication, a single-layer, wideband, differential-fed filtering antenna with high selectivity is proposed. The developed filtering antenna possesses a simple structure and consists of a square patch, a square substrate integrated waveguide (SIW) cavity, a pair of symbiotic stepped impedance resonators (SSIRs), and a pair of complementary split ring resonators (CSRRs). The SIW cavity formed with sparse metallized posts is embedded in the square patch, and the impedance bandwidth can be broadened by merging the TM10 mode of the square patch, excited by the electromagnetic energy escaping from the sparse posts, with the TE210 mode in the SIW cavity through differential excitation. The SSIRs are connected with both radiating edges of the square patch. And two extra in-band resonances together with an upper-edge radiation null are simultaneously generated, so the impedance bandwidth and the frequency selectivity at higher stopband can be significantly improved. The CSRRs, surrounding around the differential excitation ports, are etched into the bottom surface of the SIW cavity, and a lower-edge radiation null is produced to further sharpen the roll-off rate. By adjusting the geometrical parameters of the SSIRs and CSRRs, the positions of the two radiation nulls can be independently controlled. For verifying the design method, a prototype of the developed single-layer filtering antenna has been fabricated and tested. The measurement results are well consistent with the simulated values, indicating good performance with a large -10 dB fractional impedance bandwidth of 21.2%, a peak realized gain of 9.3 dBi, two out-of-band rejection levels more than 26 dB, and very high selectivity.

Design and Fabrication of a MEMS Bandpass Filter with Different Center Frequency of 8.5-12 GHz.

The design simulation and fabrication results of a bandpass filter based on micro-electro-mechanical system (MEMS) switches are presented in this paper. The MEMS filter element consists of a MEMS capacitance switch and two resonant rings that are fixed onto coplanar waveguide lines through anchor points. The micromachine characteristics of the filter could be optimized to change the center frequency from 8.5 to 12 GHz by improving the geometrical parameters; other electrical parameters of the filter, such as stopband rejection, insertion loss, and return loss at each center frequency, were simulated and calculated. In order to evaluate the MEMS filter design methodology, a filter working at 10.5 GHz fabricated with an aluminum top electrode was used, and it displayed a low insertion loss of 1.12 dB and a high stopband rejection of 28.3 dB. Compared with the simulation results, these proposed filter showed better electrical performance. Our results demonstrated that the filter with the integrated RF MEMS switch not only provides the benefit of reduced size compared with a traditional filter, but also improves stopband rejection, insertion loss, and return loss.

Low-Profile Single-Layer Half-Mode SIW Filtering Antenna With Shorted Parasitic Patch and Defected Ground Structure

A low-profile single-layer half-mode substrate integrated waveguide (HMSIW) filtering antenna with compact circuit size is presented in this brief. The antenna features simple structure and consists of a half-mode substrate integrated waveguide cavity (HMSIWC), a shorted parasitic patch, and a folded defected ground structure (DGS) etched into the metallized ground plane. The half-mode technology is employed to reduce the overall dimension in the design. The shorted parasitic patch and the HMSIWC, both operating at half-mode states, are coupled with each other to form a second-order filtering response. And also a radiation null at higher stopband is introduced owing to the effects of the cross coupling. Furtherly, by etching a folded DGS into the metallized ground plane, an additional resonance in the passband and a controllable radiation null at lower stopband are simultaneously generated to broaden the impedance bandwidth and improve the selectivity of lower stopband respectively. For verification, a prototype of the developed HMSIW filtering antenna is designed, fabricated, and measured. The measured and simulated results are in good agreement, showing a wide impedance bandwidth of 9.2% at center frequency of 2.84 GHz, a flat in-band gain response with two controllable radiation nulls at both edges of the operating band, and a maximum boresight realized gain of 5.75 dBi. The proposed HMSIW filtering antenna demonstrates good in-band and out-of-band performance even with a very low profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.015~\mathbf {\mathrm {\lambda }} _{0}$ </tex-math></inline-formula> .

Optimal High Pass FIR Filter Based on Adaptive Systematic Cuckoo Search Algorithm

Abstract This paper presents the design of a desired linear phase digital Finite Impulse Response (FIR) High Pass (HP) filter based on Adaptive Systematic Cuckoo Search Algorithm (ACSA). The deviation, or error from the desired response, is assessed along with the stop-band and pass-band attenuation of the filter. The Cuckoo Search algorithm (CS) is used to avoid local minima because the error surface is typically non-differentiable, nonlinear, and multimodal. The ACSA is applied to the minimax criterion (L∞-norm) based error fitness function, which offers a better equiripple response for passband and stopband, high stopband attenuation, and rapid convergence for the developed optimal HP FIR filter algorithm. The simulation findings demonstrate that when compared to the Parks McClellan (PM), Particle Swarm Optimization (PSO), CRazy Particle Swarm Optimization (CRPSO), and Cuckoo Search algorithms, the proposed HP FIR filter employing ACSA leads to better solutions.

A new configuration of a compact printed coplanar low pass filter with high rejection

The aim of this contribution is a new study on the achievement, fabrication and the test of a new low pass filter (LPF) coplanar structure based on periodic resonators. The proposed structure can be easly integrated with microwave devices, the validated LPF circuit has a wide band pass and high band stop. The design was done by two electromagnetic (EM) solvers one is based on moment method and the other one on finite integration technique. In order to reach a final LPF structure with good characteristics concerning the insertion loss of−0.8 dB and high attenuation until 15 GHz, the cut-off frequency of this filter is equal to 6,77 GHz. Many series of optimization were conducted using multiple algorithms. The whole area of the validated LPF is16×40 mm2.

Broadband dual‐band bandstop filters based on step‐impedance stubs and transmission‐line networks

In this paper, a novel basic structure of a dual-band bandstop filter (DBSF) without coupled lines is proposed. In order to improve the performance, some optimizations are made to the basic structure, and two DBSF structures with multi-transmission zeros and multi-transmission poles are obtained. These filters have the advantages of simple structure, high selectivity, and high stopband rejection, among which the deepest stopband can be better than 45 dB. In addition, an extraction method of transmission zeros and transmission poles based on the S-parameter theory is proposed. The ideal 3-dB fractional bandwidths of the basic structure are 37.8% and 18.7%, respectively, 54.1% and 25.9% for the first improved structure, respectively, and 75.1% and 34.2% for the second improved structure, respectively. EM simulation results and measured results are highly unified to verify the proposed filter structure.

A novel self‐packaged DBBPF with multiple TZs for 5G sub‐6 GHz applications

AbstractIn this article, we proposed a self‐packaged dual‐band bandpass filter (DBBPF) with high isolation and low insertion loss (IL) for 5G sub‐6 GHz applications. To get high stopband suppression, multiple and controllable transmission zeros (TZs) are introduced. A pair of quarter‐wavelength stepped‐impedance resonators (QSIRs) and half‐wavelength hairpin resonators (HWHR) are introduced to form a cross‐coupled five‐star topology to generate two passbands and multiple TZs analyzed by mixed electromagnetic couplings. A pair of U‐shape resonators are designed on G6 to fully excite the resonators and introduce source/load TZs at the same time. The generation of TZs by separate electric and magnetic coupling paths (SEMCP) is discussed. The DBBPF achieves a low IL of 0.85/1.13 dB with fractional bandwidths (FBW) of 11.0%/6.9% at center frequencies of 3.45 and 4.9 GHz for 5G sub‐6 GHz applications, respectively. The total size is only 0.32 λg × 0.45 λg.

A Charge-Sharing IIR Filter With Linear Interpolation and High Stopband Rejection

This article introduces a new discrete-time (DT) charge-sharing (CS) low-pass filter (LPF) that achieves high-order filtering and improves its stopband rejection while maintaining a reasonable duty cycle of the main clock at 20%. It proposes two key innovations: 1) a linear interpolation of the sampling capacitor and 2) a charge re-circulation of the history capacitors for deep stopband rejection. Fabricated in 28-nm CMOS, the proposed IIR LPF demonstrates a 1–9.9-MHz bandwidth (BW) programmability and achieves a record-high 120-dB stopband rejection at 100 MHz while consuming merely 0.92 mW. The in/out-of-band IIP3 is +17.7 dBm/+26.6 dBm, and the input-referred noise is 3.5 nV/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sqrt {\mathrm{ Hz}}$ </tex-math></inline-formula> .

Dual-Band, Differentially-Fed Filtenna With Wide Bandwidth, High Selectivity, and Low Cross-Polarization

A compact dual-band, differentially fed filtenna with wide bandwidth, high selectivity, and low cross-polarization is presented. It is composed of a slot-loaded rectangular patch, two pairs of shorting pins, a pair of novel differential coupling feedlines, and a defected ground structure (DGS). Good broadside radiation patterns with an adjustable frequency ratio (FR) between its two bands are realized. A pair of U-shaped slots is loaded on the patch to enhance the bandwidth of the lower passband. The DGS and its compact differential feedlines produce five out-of-band radiation nulls to improve the frequency selectivity of the two passbands. Simultaneously, extra in-band resonances are introduced that broaden the impedance bandwidth while maintaining a compact <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.155\lambda _{0}^{2}$ </tex-math></inline-formula> aperture size and a relatively low profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.065\lambda _{0}$ </tex-math></inline-formula> height). Prototypes were fabricated, assembled, and tested. The measured results, in agreement with their simulated values, demonstrate that it exhibits −10 dB fractional impedance bandwidths of 17.5% and 8.2%, peak realized gain values of 8.4 and 9.5 dBi, and cross-polarization levels smaller than −44 and −40 dB, in its lower and upper passbands, respectively. Its dual-band quasi-elliptic responses have sharp roll-off rates and high stopband suppression levels.

Low loss triplexer with wide stopband using CRLH-TL for WLAN/WiMAX/5G Wi-Fi applications

ABSTRACT This paper reports the design and development of a planar triplexer for WLAN/WiMAX/5G Wi-Fi applications based on a composite right-/left-handed transmission line (CRLH-TL) with low passband insertion loss, high channel isolation, wide stopband and minimal fabrication complexity. Even- and odd-mode methods are used to extract resonant properties of the globe-shaped open stub loaded stepped impedance resonator (GSOSL-SIR). The transmission line model of the GSOSL-SIR is analyzed and based on that; three bandpass filters are designed at 2.4/3.5/5.5 GHz. The equivalent LC circuit model for GSOSL-SIR-based CRLH-TL is provided with all lumped parameters fully defined. Finally, Triplexer is proposed by connecting all the three bandpass filters where each channel shows measured center frequency of 2.4/3.48/5.52 GHz with 3 dB fractional bandwidth of 22.08/22.19/16.3%. The proposed triplexer achieves high channel isolation (>30 dB) and low in-band insertion losses (1.1/0.87/1.3 dB) for the three filter channels. Additionally, the triplexer has measured 20 dB rejection levels from 6.5 GHz to 14.64 GHz and 10 dB rejection levels from 6.22 GHz to 19.85 GHz. The observed concordance between measured, electromagnetic simulated and equivalent LC circuit simulated results supports the utility of the design method.

Broadband Dual-Polarized Differential-Fed Filtering Antenna Array for 5G Millimeter-Wave Applications

This article presents a novel broadband dual-polarized filtering patch antenna array using low-temperature cofired ceramic (LTCC) process for 5G millimeter-wave (mmW) applications. The filtering antenna element is implemented using a ± 45° polarized patch antenna fed by two pairs of differential L-type probes. An additional square ring and open strips are connected to each probe, resulting in radiation nulls and realizing the lower/upper stopband rejection level over 24 dB with skirt selectivity. The cross coupling among these structures not only introduces filtering responses, but also contributes to broadening the passband of 24.25–29.5 GHz covering 5G n257/n258/n261 bands. The antenna performance is validated by equivalent circuits based on transmission line models, which reveals clearly the principles of filtering antenna step by step and provides guidelines for further designs. The proposed filtering antenna element is expanded to a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> filtering antenna array with shunt-fed feeding networks. The spacing between elements is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.48~\lambda _{0}$ </tex-math></inline-formula> . The measured results demonstrate that the array performs good filtering characters including high stopband rejection, high selectivity, and wide upper stopband up to 40 GHz, where the antenna efficiency (considering radiations from all the directions) is less than 5%. In addition, the differential feeds provide symmetric radiation patterns with low cross-polarized counterparts. Compared with other reported works, the proposed filtering antenna/array has excellent performances of wideband, high stopband rejection and wide upper stopband for potential 5G mmW applications.

Design of coaxial dual‐band filter with high stopband rejection

This paper proposes a design of dual-band coaxial filter with high stopband rejection. By setting the half-window coupling structures and loaded resonators, the stopband rejection of the dual-band coaxial filter can be significantly improved. An L band coaxial dual-band filter is designed and measured as an example. The stopband rejection of the design is increased from 2.7 times to 3.52 times the center frequency of the filter, which verifies the proposed method.

Tailoring the band-pass properties of FSS-based THz filters

High-performance THz band-pass filters are highly demanded for THz spectroscopy and imaging applications. In this work, we have analyzed the spectral features of a THz band-pass filter and divided the spectrum into three spectral regions, including a pure waveguide region, a subwavelength region and a cut-off region. Based on the understanding of the spectrum, we have proposed and fabricated two kinds of THz band-pass filters, which were characterized by time-domain THz spectroscopy and show narrow bandwidths and high stopband suppression.

Compact, Wide Stopband, Shielded Hybrid Filter Based on Quarter-Mode Substrate Integrated Waveguide and Microstrip Line Resonators

A novel miniaturized bandpass filter (BPF) with high stopband rejection based on a hybrid structure is proposed with shielded quarter-mode substrate integrated waveguide (QMSIW) and microstrip technologies. The shielded QMSIW cavity provides a high-quality ( $Q$ ) factor with substantial size reduction. This filter exhibits flexible response with four poles and two controllable transmission zeros (TZs) by incorporating two quarter-wavelength microstrip resonators into two back-to-back QMSIW resonators. The working principles for higher order mode suppression and filter coupling topology are carefully illustrated by eigen-mode simulation, coupling matrix, and field distribution analysis, respectively. Compared with the reported works, the proposed four-order BPF demonstrates advantageous features in terms of a compact size of $0.62\,\,\lambda _{0}\times 0.62 \,\,\lambda _{0}$ , a low insertion loss of 1.2 dB, a wide passband (22.7%), and a high stopband rejection (better than 36 dB).

Microwave photonic notch filter with integrated phase-to-intensity modulation transformation and optical carrier suppression.

We demonstrate for the first time, to the best of our knowledge, an on-chip microwave photonic (MWP) notch filter with high stopband rejection and integrated optical carrier suppression in a phase modulator-based system. The notch filter was achieved through phase modulation to intensity modulation (PM-to-IM) transformation and dual-sideband-processing using a network of three ring resonators (RRs) in a low-loss silicon nitride (Si3N4) platform. We show simultaneous PM-to-IM conversion and optical carrier processing for enhancing the filter performance using a single RR. We achieve filtering with a high stopband rejection of >55dB, an optical carrier suppression up to 3 dB, a radio frequency link gain of 3 dB, a noise figure of 31 dB, and a spurious-free dynamic range of 100dB⋅Hz2/3. These experiments point to the importance of vectorial spectral shaping of an MWP spectrum for advanced functionalities.