Wide-stopband Bandpass Filter Research Articles

Design of highly selective balanced bandpass filter with wide differential-mode stopband and high common-mode suppression

A highly selective and wide stopband bandpass filter (BPF) with multiple transmission poles (TPs) and transmission zeros (TZs) has been proposed. The BPF employs a box-like coupling structure consisting of two half-wavelength resonators and a dual-mode open stub loaded resonator, enabling the generation of two TZs and four TPs. Three controllable TZs are obtained by adding an annular spiral open stub to the terminal of the input and output coupling lines, which significantly improves the selectivity of the BPF. To achieve a wide stopband characteristic, a wide stopband unit with three additional TZs is cascaded within the structure. A balanced BPF is realized by introducing a microstrip-slotline-microstrip balun structure to the input and output ports of the proposed BPF. Experimental results validate the feasibility of the proposed BPF and balanced BPF applied in 2.45 GHz ISM band. The introduction of eight TZs gives the BPF a 20 dB rectangular coefficient of 1.3 with an upper stopband exceeding than 12 GHz. The balanced BPF can achieve 40 dB of high common-mode(CM) suppression in the passband, while differential-mode (DM) transmission is close to the performance of the proposed BPF. The minimum insertion loss for BPF and balanced BPF is 0.8 dB and 1.3 dB, respectively.

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.

Design of substrate integrated-waveguide wide stopband bandpass filter for 5G applications

Design of substrate integrated-waveguide wide stopband bandpass filter for 5G applications

Compact and Wide Stopband Bandpass Filters Based on Dual-Mode Folded Circular Substrate Integrated Waveguide Cavities

This article presents a novel class of compact and wide stopband bandpass filters based on dual-mode folded circular substrate integrated waveguide cavities (FCSIWCs). By employing both TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{020}$</tex-math> </inline-formula> and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{110}$</tex-math> </inline-formula> modes of the FCSIWC as resonant modes and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{010}$</tex-math> </inline-formula> mode as nonresonating mode, a doublet with two poles and two transmission zeros (TZs) is implemented. The TZs can be located either both below or both above the passband, or one below and one above. By combining the dual-mode FCSIWC and single-mode folded rectangular substrate integrated waveguide cavities (FRSIWCs), a class of compact and wide stopband four-pole box-section filters is proposed. In addition, a more selective five-pole extended box-section filter is implemented by loading a complementary split-ring resonator (CSRR) on the four-pole filter structure, without occupying any additional area. Two prototypes are fabricated and measured to validate the proposed filters.

Dual composite right/left‐handed unit with improved spurious performance and its application in wide‐stopband bandpass filter

AbstractA compact dual composite right/left‐handed (D‐CRLH) unit with improved spurious performance is presented in this study. The proposed D‐CRLH unit consists of an interdigital capacitance (IDC) and a microstrip section inductor (MSI). Compared with the traditional IDC, the proposed IDC is improved by connecting the ends of the alternate fingers through the metallic paths on the back of the substrate. Thus, the spurious resonance at low frequency is eliminated and the usable bandwidth of the IDC is extended. The meander slots are also exploited in each finger of the IDC to increase the series capacitance, which contributes to reducing the circuit size. Furthermore, the proposed D‐CRLH unit is applied in the wide stopband bandpass filter (BPF) design to demonstrate its practicability. The BPF is fabricated and measured for demonstration. The measured results are in good agreement with the simulated results.

Wide Stopband Bandpass Filter Implemented by Stepped Impedance Resonator and Multiple In-Resonator Open Stubs

Stepped impedance resonator (SIR) has been widely used for applications in wide stopband bandpass filters. However, the reported SIR wide stopband bandpass filters are limited in either stopband performance or design complexity. Here we propose an approach to improve the stopband performance and reduce the design complexity simultaneously. Two in-resonator open stubs are adopted in a SIR (with tap-feeding) to stagger the frequencies of higher-order modes (compared with other SIR) and produce two adjustable transmission zeros without affecting the fundamental properties. For a SIR filter employing such a structure, the spurious passbands are doubly deteriorated by the staggering and up to four transmission zeros. At the same time, the fundamental passband is not affected, which significantly reduces the design complexity. As a result, not only wide stopband but also high-suppression stopband can be obtained in a simple design. A prototype based on the substrate integrated coaxial line (SICL) is experimented showing an impressive stopband performance. Agreeing with the simulation well, the measured stopband is extended up to about 12 f 0 with the suppression of 40 - 50 dB (f 0 is the center frequency). The proposed technique could be very useful to design a bandpass filter with a wide and high-suppression stopband efficiently.

Substrate Integrated Waveguide Dual-Band and Wide-Stopband Bandpass Filters

In this letter, a new coupling structure implemented on a single-layer substrate and its application to design substrate integrated waveguide (SIW) dual-band and wide-stopband bandpass filters are presented. The TE101 and the TE102 modes of SIW cavity are used to design the proposed filters. By adjusting the dimensions of the coupling structure, the coupling coefficients of TE101 and TE102 modes can be controlled that can be used to design wide-stopband and dual-band bandpass filters. In the dual-band filter design, a slotline perturbation is used to lower the resonant frequency of TE102 mode while it has little effect on TE101 mode. To validate the proposed design approach, two SIW bandpass filters (wide-stopband and dual-band) are designed, fabricated, and measured.

A Compact Wide Stopband and Wide Passband Bandpass Filter Fabricated Using an SIR Technique

The demand for modern multiband and wideband communication systems is increasing. Bandpass filter architecture is widely used, and its reorganization and innovation can produce a new wideband filter. In this paper, two low-impedance stepped impedance resonators (SIRs) are strongly coupled to form an equivalent capacitor. This paper also presents a circuit that can become an inductor, a capacitor, and an inductive series resonant wide stopband bandpass filter. The center frequency of the bandpass filter is 2.3 GHz. The wide stopband frequency of the band is as high as 8.05 GHz. The center frequency can be controlled by a low-impedance capacitor when the same SIR is used in a set of architectures. In this paper, the center frequency is controlled by a 4.1 GHz series-resonant wide-stopband bandpass filter that is connected to the lower half of the transmission line. The overall circuit function becomes a wideband bandpass filter. This wideband circuit can filter up and down for a 3-dB cutoff frequency ranging from 1.9 to 4.5 GHz. The filter bandwidth is 2.6 GHz. The center frequency is 3.2 GHz.

Wide stopband bandpass filters based on quarter‐wavelength resonators

In this research, bandpass filters (BPFs) consisting of short-ended quarter-wavelength (λ/4) resonators with wide-stopband and compact size are presented. Two feed lines with loaded open stubs are coupled to the λ/4 resonators. Since the spurious passbands near even times of the fundamental frequency f 0 have been naturally suppressed by the short-ended λ/4 transmission line, only the harmonics around odd times of f 0 are remained. Transmission zeros are generated and controlled by the electrical lengths of coupled lines and loaded open stubs. They can be shifted to the locations of (2n + 1)f 0 by properly allocating the electrical length of each part. Hence, in theory all the harmonics are suppressed and broad stopband is achieved. For verification, two BPFs with different orders are designed. Measured results of the second-order BPF centred at 1.97 GHz indicate that the rejection level in the upper stopband, up to 7.1f 0 and 9.09f 0, is better than 41.8 and 27.1 dB, respectively. Simulated results of the third-order BPF reveal that the rejection level of the upper stopband up to 17f 0 is better than 32 dB. Excellent results demonstrate that the proposed BPFs are good candidates for wireless communication systems.

Resonance Characteristics of Substrate-Integrated Rectangular Cavity and Their Applications to Dual-Band and Wide-Stopband Bandpass Filters Design

Resonance characteristics of substrate-integrated rectangular cavity (SIRC) are systematically analyzed in this paper. Synthesis design techniques of substrate-integrated waveguide (SIW) dual-band bandpass filters (BPFs) and wide-stopband BPFs are demonstrated on the basis of these characteristics. The design concept of dual-band BPFs is to add some extra single-mode SIRC resonators to dual-mode resonator filters to increase the degrees of freedom in extracting direct-coupling coefficients, while the external quality factors $Q_{e}$ and cross-coupling coefficients desired in two passbands can be realized simultaneously by determining proper offset position of the I/O ports and cross-coupling window, respectively. Consequently, all the design parameters including $Q_{e}$ and coupling coefficients $M_{ij}$ required for both the passbands could be satisfied. The principle of wide-stopband BPFs is to select the constitutive SIRC resonators with identical fundamental frequency but staggered higher order ones to suppress multispurious peaks to low levels and narrow bandwidths. Then emphasis is placed on the rejection of TE202 mode, with its resonant frequency two times of TE101 for all SIRC resonators, by centered I/O ports and coupling windows. Several experimental prototypes of SIW dual-band BPFs and wide-stopband BPFs are designed and fabricated to validate these concepts. The measured results are in excellent agreement with the simulations.

Design of Wide-Stopband Bandpass Filter and Diplexer Using Uniform Impedance Resonators

This paper proposes a simple and effective method to designing wide-stopband bandpass filters and diplexers using uniform impedance resonators. Microstrip terminated parallel coupled lines are utilized to generate the filtering functions. By adjustment of the electrical lengths of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be obtained. Appropriate positioning of these zeros enables the suppression of spurious frequencies. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for both homogeneous and inhomogeneous mediums are given in detail. Different combinations of the frequency position of the transmission zeros can provide various characteristics. To extend the stopband bandwidth, one or more transmission zeros can be distributed on different harmonic frequencies. To demonstrate the proposed method, two bandpass filters and a diplexer are designed and fabricated. The measured results are in good agreement with the simulated ones. The first filter provides a high attenuation of 40 dB up to 6.8 times the fundamental frequency $(f_{{{0}}})$ and the second filter provides a lower attenuation of 28 dB, but this time extending up to $14.9f_{{{0}}}$ .

Dielectric Constant Measurement of Low Loss Materials Using NB BPF with Modified Slow Wave Resonator

Compact wide-stopband narrow bandpass filter using modified slow wave resonators is proposed. The basic filter consists of an open-stub, transmission line and coupled line. Using transmission line theory and coupled line structure, the new design methodology of a narrowband BPF is employed and resonant frequency has been clearly explained. Experimental results show that the designed filter has a fractional-bandwidth of 2 %, an insertion loss about 0.38 dB and return loss better than 30 dB. Spurious response suppression is achieved until 5f0. The overall physical size of this filter is only 23.9 mm × 10.2 mm or 0.41 źg × 0.175 źg, having a smaller size compared with conventional narrowband pass filters. The bandwidth of this filter has capability of changing with the coupled lines used in the middle of the proposed filter structure, having tunable resonance frequencies. Due to the narrow bandpass property, the proposed filter is used as a sensor to measure the dielectric constant of materials. The resonant characteristics of resonator vary with dielectric constant of the material. The proposed filter is designed, simulated and fabricated. The measured and simulated results are well complied with each other.

X‐band substrate integrated waveguide bandpass filter using novel defected ground structure cell

ABSTRACTIn this letter, an X‐band wide stopband bandpass filter is presented, which combines substrate integrated waveguide with defected ground structure (DGS) cells. Three DGS cells, including a pair of face to face modified dumbbells embedded with E‐shape slots, are adopted to achieve bandpass performance. The wide stopband is implemented by loading low pass filter, which is designed using stepped impedance open stubs, at the input/output ports. To validate the methodology, a filter with center frequency of 8.55 GHz is designed and measured, and the measured results are in good agreement with simulated ones. The designed filter has an insertion loss of 1.45 dB, a return loss of 18.8 dB in passband, and a wide upper stopband of more than 30‐dB suppression up to 45 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1156–1160, 2015

The Design of Wide-Stopband HTS Bandpass Filter

This paper presents the design of a wide-stopband HTS bandpass filter (BPF). The 9-pole wide-stopband BPF has a center frequency 2.21GHz and bandwidth 100 MHz. Based on the step impedance resonator,this filter increase the harmonic frequency to more than 3 times of fundamental frequency. Optimization simulation results shows that insertion loss is less than 0.3 dB in the passband,and stopband suppression is greater than 80 dB within 0~f0-BW and greater than 60 db within the f0 + BW ~ 3 f0. Within the passband, dB (S (2, 1)) &lt; -20. This design not only achieved a good wide stopband and solved the interference problem but also had a simple structure which is easy to implement.

Wide Stopband Bandpass Filter Implemented With Spur Stepped Impedance Resonator and Substrate Integrated Coaxial Line Technology

A novel wide stopband bandpass filter implemented with spur stepped impedance resonator (SSIR) and substrate integrated coaxial line (SICL) technology is proposed in this letter. SSIR possesses capabilities of both suppressing and staggering spurs without complicated fine-tuning, and SICL is very suitable for wide stopband applications. A prototype with compact size is fabricated, and the measured results exhibit extended stopband up to 8.76 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> with a rejection better than 40 dB (except for a little 36.5 dB burr in 7.06 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ), or 9.36 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> with rejection better than 30 dB.

Compact Wide Stopband Bandpass Filter on Multilayer Organic Substrate

We present the design and development of a compact wide stopband bandpass filter using novel quasi-lumped LC resonators on a defected ground structure. The resonators are built on a multilayer organic substrate and are coupled to external circuits by shunt-inductive impedance inverters. Experimental results show that the filter has a center frequency of 960 MHz and a 3 dB fractional bandwidth of 8%. The filter has a wide stopband that has an out-of-band rejection of better than 30 dB up to five times of the center frequency. The size of the filter is 5.4 mm × 27 mm or 0.027λg×0.132λg, where λg is guided wavelength at 960 MHz.

A wide stopband band-pass HTS filter with staggered resonators

This letter presents a novel high-temperature superconducting (HTS) band-pass filter with a very wide stopband using the method of staggered resonant modes, that is, dissimilar resonators with the same fundamental frequency but different harmonic frequencies. A new type of resonator that is suitable for this method is proposed. The design rules and design process of this method are analyzed in detail. A six-pole HTS band-pass filter centered at 500MHz with a 2MHz bandwidth is successfully designed and fabricated. Measured out-of-band rejection is better than 60dB and can reach up to 13GHz, which is about 26 times the fundamental frequency.

Design of a wide-stopband bandpass filter using stepped impedance resonators

In this paper, a compact bandpass filter (BPF) with improved stopband characteristics using stepped impedance resonators (SIRs) is proposed. The filter consists of two quarter-wavelength SIRs with radial stubs and a PI-network of capacitance, which is used to suppress the upper frequency spurious signals. An odd- and even-mode analysis is adopted considering the structure’s symmetry. A new BPF centered at 1.57 GHz has been designed and fabricated to verify the validity of the proposed method. Measured results are in good agreement with the electromagnetic simulation. The frequency selectivity was enhanced via introducing two finite transmission zeros (TZs) near the passband, located at 1.21 GHz with 43.5 dB rejection and 3.10 GHz with 62.3 dB rejection, respectively. The spurious frequencies of the upper stopband are suppressed better than 20 dB from 2.07 to 16.25 GHz. And the circuit only occupies 0.09 λg × 0.09 λg.

Full-wave analysis of a compact bandpass meandering resonator filter using method of lines

Full-wave analysis based on the method of lines and the generalized transmission line equations is applied for the design of a small-size wide stopband bandpass filter. The analytical calculation in the direction of propagation and using nonequidistant discretization enables the analysis of the method of lines to be efficient for structures that can be divided into cascaded subsections along the propagation direction of the wave. The proposed filter consists of a pair of meandering uniform impedance resonators and feeding lines. Wide stopband and high selectivity as well as compact size of the filter are achieved due to the effect of multipath between the feeding points and the resonators that leads to suppression of the first and second harmonic of the filter. The modes distribution and the scattering parameters of the designed filter are computed and studied, leading to an achievement of a passband return loss greater than 18 dB and insertion loss about 1.7 dB. The designed filter is fabricated and tested, where good agreement is found between the numerical and experimental results.

Design of a dual‐band bandpass filter with a wide stopband

A novel wide-stopband dual-band bandpass filter with a modified coupled line and lowpass filters is proposed. The modified coupled line is realised with two open stubs added to the conventional coupled line's open ends. With this proposed circuit, additional transmission zeros will appear around two passbands. Moreover, these predictable transmission zeros can be utilised to tune the two passbands’ bandwidths. Furthermore, with the lowpass filter embedded, located at the input/output port, a wide stopband can be obtained. Finally, agreement between measurement and the theoretical prediction validates the proposed structure.