Multi-band Bandpass Filters Research Articles

Design of novel multiband bandpass filters based on coupled symmetric short‐circuit stub multimode resonators

AbstractIn this letter, the working mechanism of suggested bandpass filters with connected symmetric short‐circuit stub multimode resonators is described. Because of the design flexibility, the suggested bandpass filters' centre frequencies may be modified based on the design approach. Meanwhile, the suggested bandpass filters have reduced insertion losses and compact sizes. A prototype is built and tested with six passbands centred at 1.57/2.38/3.55/5.14/5.83/6.78 GHz to confirm the design and analysis. Good agreement between the simulated, and measured results is observed, indicating that the proposed structure can be applied in the field of communication, information, and automation.

Miniaturized Multiband Substrate-Integrated Waveguide Bandpass Filters with Multi-Layer Configuration and High In-Band Isolation

This article presents a multiband bandpass filter structure with an in-line topology based on substrate-integrated waveguide (SIW) technology. A multi-layer configuration is employed to achieve circuit miniaturization. By constructing the coupling matrix, the coupling relationships among all resonators are quantitatively characterized, enabling the extraction of the theoretical frequency response and guiding circuit modeling and optimization. We designed and fabricated a third-order tri-band SIW filter and a third-order quad-band SIW filter, achieving a return loss of nearly 20 dB across all passbands. The close agreement between simulated and measured results validates the proposed design model. Additionally, the high in-band isolation of over 40 dB is demonstrated between all adjacent bands, highlighting the potential applicability of this technology in multiband scenarios.

A dual-function tunable terahertz multiband bandpass filter based on PET woven-wire meshes with conductive coating surfaces

A multifunctional terahertz (THz) device with frequency tunability, amplitude modulation and spectral filtering abilities, and substrate flexibility is highly desired for various applications, such as THz communication, sensing, wearable optoelectronics. Therefore, this study proposed a 3D artificial material based on a flexible polyethylene terephthalate (PET) woven-wire mesh with conductive coating surfaces. This material was conceptually demonstrated in experiments as a dual-functional THz device. In addition, the transmission properties of this artificial material were experimentally and numerically explored with reasonable agreement. Then, the underlying mechanism of the spectral characteristics was qualitatively elucidated. The amplitudes and frequencies of the spectral characteristics were successfully validated to be passively manipulated by tailoring the structural parameters of a unit cell and changing the surface conductivities of a device. This process opened the application feasibility of a frequency tunable bandpass filter and a power switch at the THz regime. For the bandpass filter application, the tri-frequency modulation capability was experimentally demonstrated, and a frequency tuning bandwidth of 0.249 THz was achieved by varying the conductivity of the device’s surface-coating layer from 0.44 to 77 MS/m. For the power switch application, the largest modulation depth between the on and off states of a device was successfully demonstrated at approximately 21.3 dB at 0.271 THz. This dual-function THz device has the advantages of compactness, low cost, and easy fabrication, thus providing an alternative strategy to develop tunable, flexible, and versatile THz devices for broad applications.

Multiband bandpass filter with asymmetric dual‐band response based on metacell

AbstractThe impressive growth in present‐day wireless communication systems demands compact, low‐power, cost‐effective, planar multiband microwave devices to increase the speed of communication and reduce hardware requirements, which subsequently reduce the power requirement of the system. Accordingly, this article aims to design a multiband microstrip bandpass filter with asymmetric dual‐band response based on metacell. The proposed filter is designed for wide and narrow dual‐band responses with fractional bandwidths of 72% and 2.6%, respectively. For the first time in this article, a new application of metacell in the design of dual‐band filters is discussed. A folded asymmetric step‐impedance resonator and a novel metacell structure—Dual loop split ring resonators are used to obtain wideband and dual‐band responses, respectively. The proposed work discusses the design methodology, and analysis of metacell structure based on a quasistatic model and compares simulation results with experimental results. The proposed dual‐band filter presents an insertion loss (S21) of less than 1 dB and input reflection coefficient (S11) greater than 10 dB in both passbands centered at 3.3 and 5.7 GHz. The designed filter is suitable for wireless communication applications—Wireless Access in the Vehicular Environment.

Vertically Integrated Coaxial Resonator-Based Multiband Bandpass Filters Using SLA 3-D Printing

This letter reports on a novel multiband RF filtering concept and a compact low-loss integration scheme for coaxial resonator-based multiband bandpass filters (BPFs). Size compactness is achieved by: 1) vertically stacking its constituent resonators, so that the available 3-D volume is optimally occupied; 2) the use of subwavelength capacitively loaded coaxial resonators; and 3) monolithic integration enabled by stereolithography apparatus (SLA) additive manufacturing (AM). A unique coupling routing diagram (CRD) is proposed and implemented with capacitively loaded coaxial resonators that allow to independently control the passband and stopband frequencies and facilitate both symmetric and asymmetric responses. A dual-band and triple-band BPFs operating at sub-6 GHz were designed, manufactured, and tested demonstrating highly miniaturized form factors and passbands with in-band insertion loss (IL) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> 0.2–0.3 dB, i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\mathrm{eff}}$</tex-math> </inline-formula> : 640–1030.

Design of Fractal-Based Tri-Band Microstrip Bandpass Filter for ISM,WLAN and Wimax Applications

The Peano fractal geometries exhibit a notable ability to space filling due to their distinctive characteristics. In this study, we introduce a Peano-based first-generation flat microstrip multi-band bandpass filter. The filter is presented as a possible solution for ISM, WLAN, and WiMAX applications thanks to its design with symmetric three coupled lines and asymmetric two coupled lines. The first version of the Peano fractal curve was used to design a bandpass filter with a satisfactory response at 2.44, 3.79, and 5.75 GHz. A substrate with a relative dielectric constant of 3.48 and a thickness of 0.762 mm was used to create the filter. The filter architectures' simulated performances were assessed using the CST STUDIO SUITE-based method of moments (MoM). The results show that the proposed filter architecture has good return loss and transmission properties, in addition to its reduced size and inexpensive cost

Synthesis Design of Multiband Bandpass Filters Employing Multimode Bandstop Resonators With Star-Like Topology

Multimode resonators (MMRs) can be utilized to build multiband bandpass filters (MBPFs). Each individual mode serves as the operating mode for one of the passbands in a well-known coupling topology. However, several difficulties are involved with the classical design method. In this article, we present a novel star-like topology to design MBPFs based on MMRs. Differently from the classical use, in the proposed novel topology, they are so regarded as bandstop resonators and provide multiple controllable transmission zeros. To explain the proposed concept and the implementation method, two bandstop MMRs – a classical dual-mode stub loaded resonator (DSLR) and a new tri-mode dual-stub loaded resonator (TDSR) – are investigated with detailed design formulas and diagrams. Then, a tri-band MBPF with equal individual sub-bands, a quad-band and two quint-band MBPFs with unequal individual sub-bands are synthesized and designed using the proposed bandstop MMRs. Additionally, simulations and experiments are used to verify the efficiency of all prototypes. Good agreements with the theoretical calculations are observed for all the MBPFs.

Analytical Design of Compact Multiband Bandpass Filters with Multiconductor Transmission Lines and Shunt Open Stubs

A compact topology for implementing compact multiband bandpass filters is presented in this paper. To achieve the desired frequency response, two identical short-circuited multiconductor transmission lines (MTLs) and properly connected shunt open stubs are interconnected. Using this configuration, it is possible to design multiband bandpass filters effortlessly. As both the MTLs and the stubs are distributed elements, spur-line band-stop filters are added to mitigate the first replica of the structure’s frequency response. To assess the behavior of the developed filter design procedure, a prototype consisting of a six fingers-MTL and two shunt open stubs has been designed, manufactured, and analyzed, showing excellent agreement between analytical and measured results, considering that no simulation or optimization process has been performed during the design process, just for result verification. Furthermore, it is possible to establish a design criterion that allows the fast and reliable synthesis of multiband responses by varying just a small number of geometrical parameters of the MTLs and the corresponding stubs.

Design of Multiband Bandpass Inline Topology Filters Using Compact Multicoupled Line Structures

This paper presents the synthesis and design of multiband bandpass filters (MBPFs) with in-line topology. The coupled-line coupling structures are employed to achieve multi-channel responses and compact footprint. Two different approaches are developed in this research to implement coupled-line MBPFs based on frequency transformation methods. The first synthesis method is based on the direct mapping technique. According to this method, a quad-band bandpass filter is theoretically synthesized and designed. The second proposed method is based on generlized ladder-type network analysis with frequency-invariant reactance elements (FIRs). It enables designing MBPFs with arbitrary number of passbands. To validate this method, a sext-band MBPFs is theoretically investigated, synthesized and designed in microstrip technology as well. Very good in-band filter performance and very good band-to-band isolation are observed for the proposed MBPFs. These results show that the proposed synthesis methods and structures are attractive solutions to design MBPFs with coupled line technology.

A Survey on Microstrip Single/Multiband Bandpass Filter for 5G Applications

For a long time, extensive research on microstrip bandpass filters has been documented to meet the standards of modern multiservice wireless communication systems. The multiband bandpass filters (BPF) are required for the receiver front end to function as a single device that caters to many bands at the same time. Planar bandpass filters are particularly promising because of their simplicity of manufacture using printed circuit technology, compactness, and low integration cost. Due to the need for high integration, low cost, and high-speed data transmission, the design and implementation of filters for fifth-generation (5G) mobile communication systems is difficult. This paper presents and discusses a detailed survey of existing research on microstrip singlemultiband bandpass filter designs for fifth-generation applications, with a focus on the latest advancements in this research and the difficulties that researchers face. Various designs and techniques were given. A detailed comparison of several design techniques is presented and discussed to offer researchers the benefits and drawbacks of each technique and design that may be of interest to a certain application. Recent microstrip single/multiband BPFs are included in the surveys, which use different design techniques and achieve varying performance for current and future fifth-generation applications.

Substrate Integrated Waveguide Multiband Bandpass Filters and Multiplexers: Current Status and Future Outlook

Multiband bandpass filters (BPFs) and multiplexers are essential front-end modules in the development of multifunction, multistandard, and multiband wireless communication, sensing, and positioning systems that are required in current and future intelligent electronics applications. In this paper, numerous implementation schemes and topologies of multiband BPFs and multiplexers, which have been proposed, studied, and developed so far, are holistically summarized and elaborated in terms of their merits and drawbacks. Subsequently, various technical approaches and diverse design methodologies based on substrate integrated waveguide (SIW) technology are thoroughly examined and reviewed with respect to technical features, electrical performances, and practical applications. Finally, future research and development directions and prospects of SIW multiband BPFs and multiplexers are briefly unraveled.

Селективные свойства двухрезонаторных структур и высокоизбирательные фильтры на их основе

An increase in the frequency selectivity of microstrip filters is traditionally achieved by forming transient response zeros at final frequencies. In this case, the specified requirements for the selectivity of filters are provided with a smaller number of resonators, and, consequently, lower loss es in the passband are achieved in more compact structures. Thus, the effectiveness of this approach to the synthesis of microstrip filters is determined by the number of transient response zeros that can potentially be formed in various structures. One way to form damping transient response zeros is to introduce additional cross-couplings between non-adjacent resonators. However, when synthesizing highly selective filters based on such widely used N-resonator structures, a limited number of transient response zeros equal to N-2 is formed. At the same time, two-resonator structures are known in which a much larger number of transient response zeros is formed, which is several times greater than the number of resonators in them. However, each of these structures has its own specific frequency-selective properties, which limits the scope of their wide application as universal links. The aim of this work is the synthesis of highly selective two-cavity structures with various types of frequency characteristics, which expands the scope of such structures. The frequency properties of microstrip two-resonator structures of a new type, which have broad functionality and increased frequency selectivity, are studied. It is shown that in multistage structures on two half-wave hairpin resonators, under certain conditions, a significant number of transient response zeros is formed, which is two to three times greater than the number of resonators in the filter, and parasitic transmission bands also degenerate. Depending on the ratio of the coefficients of electromagnetic interaction in different sections of the length of the coupled resonators, they acquire the properties of both single-band and multi-band bandpass filters, as well as low-pass filters. The noted features predetermine the possibility of wide application of these structures as both independent compact filters and basic units as part of higher-order filters with a significantly limited number of resonators. The results of electrodynamic 3D modeling and experimental studies of the proposed structures are presented, which are in good agreement.

Development of highly selective compact high-temperature superconducting quad-band bandpass filter using interdigital feeding structure for radio astronomy

Astronomers at the Mizusawa Very Long Baseline Interferometry Observatory of the National Astronomical Observatory of Japan are promoting the development of broadband receivers in the ultra-high frequency (UHF) band. The presence of extensive radio frequency interferences (RFI) in the UHF band hinders continuous broadband radio observations in this band. A promising technical solution to this problem is to use a superconducting multi-band bandpass filter as it enables the bundling of several RFI-free bands. We have developed a high-temperature superconducting compact quad-band bandpass filter (QB-BPF) at 0.7, 1.4, 1.6, and 2.1 GHz with low loss and steep cutoff characteristics for broadband receivers. That consists of two six-pole dual-band bandpass filters. We have devised an interdigital feeding structure with a high degree of freedom that enables the external quality factor to be designed individually for each band. A compact QB-BPF was fabricated using double-sided YBa2Cu3Oy thin films on a 36.4 mm × 42.0 mm (0.22λ g × 0.25λ g) Al2O3 substrate. The measurement results agreed well with the simulated ones, indicating that the QB-BPF overcomes the problem of extensive RFI in the UHF band.

Compact multiband bandpass filters based on parallel coupled split structure multimode resonators

In this letter, a novel sext-band bandpass filter (BPF) using two split-type multiple-mode resonators is proposed. The filter is composed of two sets of resonators which are respectively designed to realize Filter 1 with two passbands and Filter 2 with quad passbands. Then the two BPFs are combined by parallel coupling feed lines for sext-band responses, and each of the six centre frequencies in the proposed sext-band BPF is able to be controlled due to the design freedom. To validate the design and analysis, a prototype filter has been fabricated with six passbands centred at 1.88/2.59/3.48/5.26/5.82/6.75 GHz. The measured result of the fabricated filter agrees well with the simulation, which shows that the proposed structure is a good candidate for sext-band BPF designs and validates the proposed design flow well.

Design of 3-D Integrated SIW Multiband Bandpass Filter With Split-Type Extended Doublet Topology

A new class of 3-D integrated multiband bandpass filters (BPFs) based on substrate integrated waveguide (SIW) technology is presented in this work, for the first time. Split-type dual-extended doublet (SDED) coupling topologies are developed to propose these BPFs with a desired multiband response by the LEGO-style assembly of planar SIW resonant-mode blocks. These design schemes offer attractive and promising advantages with regard to compact size, low cost, flexible and expandable topology, as well as integration of high-density integrated circuits. For demonstration, dual- and triple-band BPFs are designed, fabricated, and measured. The measurement results are in good agreement with the simulation ones. Results indicate that the proposals can provide not only nice selective multiband signal transmission in such flexibly extensible topologies with new spatial schemes but also increase space utilization and reduce footprint.

Coupling Matrix Design of Compact Multiband Cascaded Trisection Bandpass Filters

In this brief, a universal coupled topology to design cascaded multiple passbands bandpass filters (BPFs) with numerous in-band poles and out-band transmission zeros (TZs) is presented. Based on the proposed topology, the coupling matrices are constructed to design multiband bandpass filters (MBPFs) with cascaded trisection (CT) BPFs’ filtering responses. To validate the theory and topologies, a quad-band CT BPFs with TZs located in each lower sub-band is successfully synthesized firstly. Then, a dual-band and tri-band CT BPF with TZs generated in the upper side of each passband are theoretically investigated by employing the coupling matrix. Finally, the proposed dual- and tri-band examples are implemented in compact planar multi-coupled lines structures. In all individual passbands, measured insertion losses (ILs) and measured return losses (RLs) are better than 2.82 dB and 15.9 dB, respectively. Good matching level between the simulated and experimental results have been achieved.

Miniaturized Multiband Bandpass Filters Based on a Single Multimode Resonator Loading Branches

In this paper, the operating mechanism of proposed bandpass filters with a single multimode resonator loaded with branches is introduced. Based on the design procedure, the center frequencies of the proposed bandpass filters can be controlled due to the design freedom. Meanwhile, the proposed bandpass filters (BPFs) feature compact sizes and small insertion loss. To validate the design and analysis, a prototype was fabricated and measured with six passbands centered at 1.23/1.76/2.38/4.24/5.23/6.75 GHz. The measured result of the fabricated filter agrees well with the simulation, which indicates that the proposed structure can serve as a potential candidate for multiband BPF designs.

New microstrip multiband filter for modern wireless applications using Kappa substrate material

In this paper, a new multiband bandpass filter using Kappa substrate has been designed to be operated under resonant frequencies of 3.02 and 3.56 GHz for the first band, 6.2 GHz for the second band, and 7.1 GHz for the third band with excellent scattering parameters. The projected filter employs dual microstrip elements of non-symmetric step impedance resonators and uniform impedance resonator and microstrip feeder based on symmetric step impedance resonator. The filter has been in agreement simulated S11 and S21 scattering parameters using AWR and Sonnet electromagnetic solvers.

New highly narrowband miniature microstrip bandpass and bandstop filters based on SIR components for wireless systems

ABSTRACT This study presents new miniaturized designs of microstrip multiband bandstop filter (BSF) and multiband bandpass filter (BPF) employing step impedance resonators (SIRs) and RT/Duroid 6010 substrate. The projected bandstop filter can be adopted in applications for removing the interference of narrowband signals from the allocated bands of other wireless systems operated under 2.5, 5.84, and 9.79 GHz. On the other hand, the designed bandpass filter can be used in RF transceivers operating in various isolated narrow frequency bands at operating frequencies of 5.35, 5.555, 6.36, 7.84, 8.385, and 9.5 GHz. The novelty of this paper comes from the considerable smallness of the designed filters and extremely low fractional bandwidths (less than 1%) as compared with numerous reported filters in the literature, especially the superconducting filters. Both filter designs have been verified through measurement, and the measured consequences are in line with the simulation ones.

A novel asymmetrical interdigital coupled line‐based penta‐band bandpass filter design with enhanced selectivity employing square complementary split ring resonator

This article demonstrates design of a novel miniaturized penta-band bandpass filter (BPF) having enhanced selectivity with 10 transmission zeros (TZs) employing asymmetrical interdigital coupled lines and square complementary split-ring resonators (SCSRR). The arrangement of a split in open-circuited stubs with SCSRR presents an independently controllable additional TZ. The measured minimum insertion losses and shape factors are 1.1, 0.95, 1.35, 1.5, 1.65 dB and 2.1, 1.6, 1.7, 1.85, 1.7, respectively. Hence, this futuristic design structure with five passbands prominently delivers improved selectivity and low-insertion loss compared with other progressive multi-band BPFs. The fabricated penta-band BPF's physical area is 17.5 × 28.5 mm2 and renders five passbands operating at 1.8, 2.4, 3.5, 4.9, and 5.8 GHz for GSM, Wi-Fi, Wi-Max, public safety applications, and WLAN applications, respectively.