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This article presents the design of a compact notch filter with a sharp roll-off and high rejection over a wideband. The filter comprises stepped impedance resonators that are interconnected to each other at strategic points on the resonator for optimal 3 dB roll-off and high rejection over a wide stop-band. The fabricated third-order filter exhibits a steep 3 dB roll-off and rejection exceeding 50 dB over the frequency range 2.70–6.19 GHz.

A novel coaxial stepped-impedance resonator (SIR) filter is proposed based on conventional multi-layer printed-circuit board (PCB) technology. The resonator results in a measured unloaded quality factor (Qu) of 185 at 3.7 GHz, has compact size, is self-shielded and has very low electromagnetic (EM) coupling to nearby RF circuits. The 3-D filter topology easily lends to advanced filter design with multiple transmission zeroes using cross coupling and source-to-load coupling on the top printed-circuit board layer. Two third-order fixed-band bandpass filters, and two fourth-order tunable bandpass filters are demonstrated in this technology. The fixed-band filters have an insertion loss of 1.6 dB with a fractional bandwidth of 6.5% at 3.6 GHz and occupy a size of 9 × 12 mm 2 . The tunable filter covers 2.1-2.9 GHz with a fractional bandwidth of 3.5%, and an insertion loss of 4.2-9.2 dB, limited by the silicon varactors. Multiple transmission zeroes are used in these designs to significantly improve the filter selectivity. Application areas are in fixed and tunable filters with very compact size and high shielding from nearby circuits for advanced communication systems.

One of the most critical aspects of virtual analog simulation of circuits for music production consists in accurate reproduction of their nonlinear behavior, yet this goal is in many cases difficult to achieve due to the presence of implicit differential equations in circuit models, since they naturally map to delay-free loops in the digital domain. This paper presents a novel and general method for non-iteratively implementing these loops in such a way that the linear response around a chosen operating point is preserved, the topology is minimally affected, and transformation of nonlinearities is not required. This technique is then applied to a generalized model of the Moog ladder filter, resulting in an implementation that outperforms its predecessors with only a modest computational load penalty. This digital version of the filter is shown to offer strong stability guarantees w.r.t. parameter variation, allows the extraction of different frequency response modes by simple mixing of individual ladder stage outputs, and is suitable for real-time sound synthesis and audio effects processing.

In this study, a three-input single-output voltage-mode biquadratic filter employing voltage differencing differential input buffered amplifier (VD-DIBA) is presented. The proposed filter uses two VD-DIBAs and two grounded capacitors without any external resistors, which is well suited for integrated circuit implementation. The circuit provides five standard transfer functions, namely, low pass, high pass, band pass, notch and all pass filters with electronic control of quality factor and pole frequency. Each transfer function can be selected by suitably selecting input signals via digital method. The filter does not require inverting of the input voltage signal. Moreover, the circuit possesses high input and low output impedances and thus it enables simple voltage-mode cascading. The PSPICE simulation and also experimental results are included, verifying the workability of the proposed filter. The given results agree well with the theoretical anticipation.

In this study, a second-order Chebyshev active bandpass filter with three finite transmission zeros at C-Band is presented. This filter utilises an active capacitance technique to compensate resistive losses of resonators, and a shunt-feedback inductor between input and output to achieve the transmission zeros in the bandpass filter. Moreover, one transmission zero is in the lower stopband, and two transmission zeros are in the upper stopband, thus improving the selectivity of the filter significantly. The filter is designed and fabricated in a standard 0.18 μm CMOS technology with a chip area of 0.92 mm × 0.76 mm including all testing pads. The filter achieves 0.77 dB insertion loss, 18 dB return loss, and 32% 3 dB bandwidth at 5.3 GHz with 2.2 mW power consumption. The measured NF and input P1 dB is 4.3 dB and 2.5 dBm, respectively. Finally, the rejection levels at these transmission zeros are greater than 14.4 dB.

Microstrip/coplanar waveguide (CPW) hybrid bandpass filter with electromagnetic (EM) coupling has been developed, and a hybrid tri-band bandpass filter has been proposed. For each passband, the filter center frequency can be easily controlled, and the bandwidth can be adjusted. The hybrid bandpass filters have simple topologies, high frequency selectivity, and multiple passbands. The tri-band filter has been fabricated and measured, and the design has been demonstrated.

A novel balanced differential bandpass filter implemented in coplanar waveguide (CPW) technology is presented. The filter is based on the use of two magnetically coupled CPW folded-stepped impedance resonators. The use of magnetic coupling, instead of the more common electric coupling, provides inherent common-mode rejection. Measured and simulated results demonstrate the benefits of the proposed balanced filter.

This paper presents a compact triple-band bandpass filter based on metamaterials. The miniaturization is realized by the principle of phase compensation of metamaterial. Compared with the conventional half-wavelength filter, the metamaterial filter has a small size of 10 mm×10 mm. The triple-band bandpass filter performance has been validated by the electromagnetic simulation software of high frequency structure simulator (HFSS). The results illustrate that the filter is designed with center frequencies of 2.4 GHz, 5.1 GHz and 8.8 GHz, bandwidths of about 7.9% (2.31—2.50 GHz), 7.8% (5.0—5.4 GHz) and 7.4% (8.50—9.15 GHz), respectively, and it shows good band pass characteristics.

In this work, a new ultra-wideband (UWB) bandpass filter (BPF) with notch band (NB) at 5–6 GHz is presented. The design is performed using the impedance matching method based on optimization of objective function defined in the frequency range 3.1–10.6 GHz. The filter structure is composed of uniform transmission line loaded, at its center, with stepped impedance stub to generate two transmission zeros at cutoff frequencies, and uniform transmission line stub for NB purpose. The fabricated filter has a compact size of 306.17 mm2 and fulfills the UWB BPF specifications with a sharp selectivity and an efficient cancellation of two Wireless Local Area Network frequencies (5.2 and 5.8 GHz). © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2176–2178, 2016

A quasi-elliptic function bandpass filter (BPF) based on parallel feed topology is presented. The parallel feed topology is realised by splitting the input/output port of the filter into two paths through a T-junction to excite a pair of resonators simultaneously. This configuration contributes to further improving the selectivity of the filter by introducing more transmission zeros (TZs) near the passband. In addition, a defected microstrip structure is utilised to enhance the out-band attenuation and spur suppression. In order to verify the proposed topology, a fourth order BPF with cross-coupling is designed, fabricated and measured. The measured frequency responses agree well with simulated ones. Four TZs can be obtained with two TZs on each side of the passband.

In this letter, a novel direct coupling matrix synthesis approach is proposed for the narrowband mixed topology filter (i.e., the filter structure part with extracted-pole and part with cross-coupled configurations). First, canonical coupling matrix for the filter is constructed based on a set of new characteristic polynomials with complex coefficients to generate extracted-pole sections at the source and load directly. Then, a specific matrix rotation sequence is introduced to reduce the filter to a more practical N-tuplets & extracted-pole mixed topology. For validation purposes, two illustrative examples are given. As the synthesis is done by a simpler coupling matrix process, the presented approach provides a more convenient solution for synthesizing mixed topology filters with terminal extracted-pole sections.

In this letter, we present a new absorptive bandstop filter topology that is capable of operating in the microwave regime (C-Band) and is capable of creating large attenuation using resonators which are comprised of printed circuit elements and surface mount elements. This particular topology allows for a high level of miniaturization when compared to transmission line realizations. Simulated and measured results are presented and show good correlation. We demonstrate a prototype absorptive bandstop filter that operates within the C-band, achieves $>$ 50 dB of rejection, and has a total size of 7 mm $\times$ 8.2 mm.

In this paper a narrow band band-pass filter with a wide upper stopband using short-circuited microstrip coupled-lines is presented. This filter can be implemented easily by using single layer microstrip. The equivalent transmission line circuit model is used to achieve a useful analysis of the proposed filter performances. To validate the design and analysis, the band-pass filter is designed, simulated using the full-wave EM simulator ADS and fabricated on a 31 mil thick RT/Duorid 5880 substrate with a relative dielectric constant 2.2 and loss tangent of 0.0009. The measured results show that it can operate at 2.41 GHz and up to the 19.2 GHz 20 dB stopband. The filter is evaluated by experiment and simulation with a good agreement.

A new single substrate-integrated bandpass-bandstop (BP-BS) filter cascade, implemented using high-Q, heavily-loaded, evanescent-mode cavity filters, is presented. The cascade has the capability of dynamically tuning its passband and stopband at any two independent frequencies within a frequency range. A modular design approach is used to design the cascade by directly cascading synthesized coupling matrices of bandpass and bandstop filters. To demonstrate the concept, a 4% second-order Butterworth bandpass filter is integrated with a second-order Butterworth bandstop filter, with 2% fractional bandwidth at 10-dB rejection, to form a cascade that can be tuned continuously from 3000 to 3600 MHz. Measurement shows that a filter cascade with insertion loss as low as 0.9 dB and isolation as high as 100 dB is feasible.

This letter presents a novel reconfigurable dual- band bandpass filter (DBBPF) with independently controlled passbands and constant absolute bandwidths (ABW). The design procedures follow the traditional synthesis approach of filters. Moreover, in order to meet the requirement of constant ABW, theoretical analysis and calculation are carried out to determine proper parameters of coupling regions. Finally, the proposed DBBPF exhibits 21.8% fractional tuning range of the first passband from 0.98 to 1.22 GHz and 17.9% of the second passband from 1.63 to 1.95 GHz, and 3-dB ABWs are 76 $\pm$ 4 MHz and 100 $\pm$ 4 MHz, respectively.

A tunable balanced bandpass filter using a short coupled-line resonator is proposed. The design aims at achieving a wide tuning range in the differential-mode for both of the center frequency and bandwidth with high common-mode suppression. The proposed filter uses a short section (about one-eighth of one wavelength) of parallel-coupled lines connecting the differential ports of the device and five pairs of varactors. A theoretical analysis using the even-odd mode theory is presented to verify the tunability of the design and calculate the initial values of its design parameters. For validation, a prototype is designed, fabricated and tested. The measured results indicate that the differential-mode tuning range for the center frequency and 3 dB- bandwidth extend from 0.58 to 1.22 GHz, and from 65 to 180 MHz, respectively, with more than 30 dB of common-mode suppression in the operating differential-mode passband. Moreover, the proposed device has a compact size (with respect to the guided wavelength) of only $0.12\lambda_{G}\times 0.08\lambda_{G}$ .

A low-noise tunable filter with high dynamic range and minimum power consumption is presented and addressed with circuit details. It is based on an active solution simulating an inductive behaviour that allows improving the filter quality factor without affecting the noise performance. The low-order bandpass filter is realised with minimum number of components and it is suitable to be integrated in integrated circuit or used in hybrid transceiver and modern reconfigurable radio systems. A prototype board with discrete components has been fabricated and tested with good results.

A novel fifth-order suspended stripline (SSL) low-loss bandpass filter with four transmission zeros is proposed. The technique of utilising only one cross-coupling structure introduces four transmission zeros to provide high selectivity. By adjusting the parameters of the coupling open loop, the performance of out-of-band of the filter can be changed. A detailed discussion of this effect of the coupling open loop is given. The highest out-of-band rejection of the filter is more than 70 dB. An SSL bandpass filter is designed, fabricated and measured. The measured results are in good agreement with the simulated results.

In this paper, a multi-objective optimal design for transformerless hybrid active power filter (HAPF) is proposed. The interactions between the active and passive circuits is analyzed, and by taking the interactions into consideration, a three-dimensional objective problem comprising of performance, efficiency and cost of HAPF system is formulated. To deal with the multiple constraints and the strong coupling characteristics of the optimization model, a novel constraint processing mechanism based on distance measurement and adaptive penalty function is presented. In order to improve the diversity of optimal solution and the local searching ability of the particle swarm optimization (PSO) algorithm, a chaotic mutation operator based on multistage neighborhood is proposed. The simulation results show that the optimums near the ordinate origin of the three-dimension space make better tradeoff among the performance, efficiency and cost of HAPF, and the experimental results of transformerless HAPF verify the effectiveness of the method for multi-objective optimization and design.

In order to ensure the normal operation of mobile devices in the Wi-Fi band without interference from adjacent frequency bands, a BAW filter for the Wi-Fi 802.11b band (2402-2482 MHz) is designed. An initial structure ladder filter based on a one-dimensional Mason equivalent circuit model of thin-film bulk acoustic resonator (FBAR) is designed. The resonance area value of series FBARs and the ratio of resonance area value of parallel FBARs to series FBARs are made into two types of optimization parameters reasonably. According to the required insertion loss and out of band rejection of filter as the optimization objective, the optimized values are obtained by the algorithm based on gradient and genetic in ADS software. In order to make the simulation results more accurate, the combined acoustic-electromagnetic method is used to simulate and compare with the simulation results of the Mason equivalent circuit model in the filter design process. The results show that the performance of the filter is decreased, insertion loss increased 1.6 dB, ripple increased 1.1 dB, out of band rejection is basically the same. The design of Wi-Fi band BAW filter has low insertion loss (less than 3 dB) and high out of band rejection (more than 40 dB) performance.

We propose a structure of a cascaded chirped narrow bandpass filter with a flat-top based on two-dimensional (2D) photonic crystals (PhCs). The filter discussed here consists of three filter units, each with a resonator and two reflectors. Coupled mode theory and transfer matrix method are methodologies applied in the analysis of the features. The calculations show that the bandwidth of the filter can be adjusted by changing the distances between resonators and reflectors, and based on this, a flat-top response can be achieved by chirped-cascading the filter units. According to the theoretical model, we design a narrow bandpass filter based on 2D PhCs with a triangular lattice of air holes, the parameters of which are calculated using the finite element method. The simulation results show that the filter has a center frequency of 193.40 THz, an insertion loss of 0.18 dB, a flat bandwidth of 40 GHz, and ripples of about 0.2 dB in the passband. The filter is suitable for dense-wavelength-division-multiplexed optical communication systems with 100 GHz channel spacing.

In order to reduce the volume of the filter and increase the number of chips on the wafer, while ensure the filter performance, a design method of the bulk acoustic wave (BAW) ladder filter is proposed. This layout design method consists of 11 design criteria and a 6-step flow. The 11 design criteria limit the shape and position of the BAW resonators (BAWRs), the distance between the BAWRs, the distance between the BAWRs and the pads and the interconnecting wire. The layout design flow has 6 steps. 1) Preset the shape of each BAWR (square/pentagon) according to its active area values. 2) Add an auxiliary circumcircle for each BAWR, tightly align all the series resonator circumcircles along a central line in order, and mate the corresponding electronically neighboring parallel resonator circumcircles one by one at a position above/below the center line. This makes an initial 3-row and n-column 2D arrangement, and the column number N is determined by the filter order. 3) Fix the very first series resonator circumcircle position and incrementally "compress" the initially self-assembled 3-row structure along the row width direction until the row height for row width bargain is no more cost effective. 4) Apodize the square series resonators and fine-tune each resonator's shape and rotation according to above-mentioned related design criteria. 5) Wiring BAWRs and pads together. 6) A combined acoustic-electromagnetic BAW filter simulation method is used to validate the layout result. In a 5-order BAW ladder filter layout demo case, a layout fill ratio over 44% is obtained. An autolayout program "BAW-filter Auto-layout Tool (BAT (R))" based on the presented method is also presented.

A hybrid active filter with a new voltage synchronization control loop is proposed to improve the harmonic content of nonlinear active front end converters for mobile mining equipment. This hybrid filter topology utilizes the DC bus established by the AFE and provides load harmonics at the PCC. Unlike traditional hybrid active filters, this topology uses no real power or control loops to maintain a DC link as this is provided by the AFE. This paper investigates the hybrid active filters performance in two compensation modes, harmonic current only, and both harmonic current and reactive power injection. Necessary considerations for the medium voltage dc testbed topology, real power flow minimization, and the active filter control during worst case load harmonic currents are also discussed.

In this paper, a coupling matrix based method is used to synthesize a bandpass filter. The designing method is independent of change in source and load impedances. The proposed filter is synthesized by frequency transformation from lowpass prototype to bandpass filter. The MATLAB code is developed for frequency transformation and coupling matrix is generated. The filter is designed on RT/Duroid substrate with relative dielectric constant of 10.8 and thickness of 1.27 mm. The filter is designed and simulated on HFSS and response is found in good agreement with the response found from mathematical model.

This paper presents a new type of cross coupled low loss and high selectivity bandpass filter operating at millimeter wave band. The filter is designed based on groove gap waveguide technology. A Ka-band 4th-order bandpass filter is proposed, designed and fabricated. Cross coupling between a one pair of non-adjacent resonators has been introduced to produce two transmission zeros at the frequencies below and above the passband. The designed filter, which operates at a central frequency of 35.65 GHz with a fractional bandwidth of 1%, is fabricated using CNC milling machine. A reasonable agreement between the measured and simulated results has been obtained. Most design specifications are met although the measured insertion loss and return loss are not as good as the predicted which may be due to discrepancy between the material properties and fabrication errors.

In paper, the technique of generation of all possible structures of digital filters with the fixed number of nodes is offered. As a mathematical model of the structure of the digital filter, a topological matrix of the transmission coefficients between the nodes of the structural scheme was used. Templates have been built for the formation of specific structural schemes. Structural units of block diagrams and rules for their connection are singled out.

This paper presents a planar tri-band bandpass filter with high out-of-band rejection over a wide band. The filter is based on two pairs of λ/4 resonators embedded inside an open loop ring resonator without any size increase, where each pair of resonators are electromagnetically coupled to each other and the feedlines. This results in the excitations of passbands, where the first passband is generated by the open loop resonators. The second and the third passbands are excited by λ/4 resonators. The proposed technique provides sufficient degrees of freedom to control the center frequency and bandwidth of the three passbands independently. In addition, the six transmission zeros created around the passbands results in a tri-band filter with high selectivity, sharp 3 dB cut-off frequency, high isolation, low passband insertion-loss and high out-of-band harmonic rejection across an ultra-broadband frequency range up to 17 GHz. The proposed technique has the ability to switch from triple to dual band by removing one pair of the inner resonators. Design methodology and simulation results of the filter are provided.

In this paper, a compact third-order bandpass filter with Chebyshev characteristic is designed by using integrated passive device (IPD) technology. The filter is capacitively coupled and consists of three parallel resonators. The simulation results show that the center of the filter Frequency of 1700MHz, bandwidth of 500MHz, the volume is only 1.0mm*0.5mm*0.3mm.

A miniaturized second-oder Inductive Coupling band-pass filter based on low temperature co-firing ceramic (LTCC) technology was designed in this paper, The coupling effect between the two resonators is used to further reduce the size of the device. On the basis of this filter, the simulation of the surface paste varactor diode and then achieve the center frequency adjustable. The filter model is established and simulated in the three-dimensional electromagnetic field simulation software HFSS. The results show that the center frequency of the filter can be continuously changed in the range of 1.05GHz ∼ 1.23GHz, the insertion loss is kept below 1dB, the return loss is always greater than 15dB, the out-of-band suppression is better than 45dB at 2fo, the overall size is 6.5mm × 4mm × 0.9mm.

A dual-mode dual-band cavity is proposed for the integration of compact dual-band filters with widely separated passbands. The basic structure is a cavity working on two distinct dual-modes, realizing a four-pole dual-band filtering function. An intermediate structure is also designed to validate coupling between dual-band cavities. Finally, two dual-mode dual-band cavities are coupled together for implementing an eight-pole filter with two passbands at 5 and 7.5 GHz, respectively. Prototypes are fabricated and measured for validating all designs, showing the relevance of the proposed concept.

This paper presents a third order coupled bandpass filter using integrated passive device technology and SIR architecture. The filter is based on the semiconductor wafer IPD process, using thin film technique and photolithography technology, combined with the advantages of high harmonic suppression of the SIR. Compared with passive device process such as LTCC (low temperature co-fired ceramic), this filter has a smaller volume and higher degree of integration. The results show the filter only occupies the area of 1.4mm × 0.8mm.The bandpass filter exhibits low insertion loss around 1.5dB, the return loss around 20dB, center frequency at 5.96GHz. The passband voltage standing wave ratio (VSWR) is less than 1.5.

An active inductor based on voltage differencing voltage transconductance amplifier (VDVTA) as an active element is presented. Using the active inductor, a bandpass filter is designed and the effect of process and current variations on the characteristics of the active grounded inductor-based bandpass filter is demonstrated. The bandpass filter shows its robustness against process and current variations. The simulation of the presented circuit is done using Virtuoso Analog Design Environment of Cadence @ 45-nm CMOS model parameters.

In this paper, a new area-effective complex-filter topology which can be used as an image-reject filter in low-IF receiver is proposed. A first-order image-reject filter obtained according to a new topology which corresponds to a complex shunt RC circuit. To demonstrate the usefulness of filter, simulation results of the filter are obtained by using SPECTRE in the CADENCE design tool.

One of the methods to improve the power quality in electric power networks is the use of active power filters. In the article, a method of analysis of transition and quasi-steady state processes in a shunt active three-phase power filter (SAPF) was presented. The analysis of electromagnetic processes was carried out on the basis of a mathematical description of the active filter. Structural models for the simulation of dynamic processes in the shunt active three-phase power filter were developed. The results of studies of dynamic states obtained for the SAPF with independent control and current control were shown. A study of the active filter was performed with the use of Matlab-Simulink program.

This paper introduces an ultra-wide band (UWB) band pass filter (BPF) with a coupled T-shaped stub. The filter's lower cut-off frequency and higher cut-off frequency are around 3.2 GHz and 9.7 GHz respectively. Moreover, the pass band exhibits two narrow notches at 5.9 GHz and 7.8 GHz which minimize the interference effects of the proposed filter with both the wireless local area network (WLAN) and SATCOM systems, respectively. The main pass band of the filter and the upper notch are implemented using a stepped impedance resonator, coupled with an inter-digital feeding line backed by defected ground structures (DGS) for coupling augmentation. The lower notch band is implemented using a stepped impedance stub that is grounded through a via hole at one end and coupled to the main filter form at the other end. The proposed filter features a small size of 0.443× 1.534 λ g 2.

Future software-defined radios (SDRs) for modern wireless applications—e.g., 5G communications—could require reconfigurable RF analog circuits to enable multistandard/service operation with hardware miniaturization. In this context, a lumped-element multi-band bandpass filter concept is presented. This filter architecture consists of the in-series cascade of several multi-transmission-zero-(TZ)-generation cells that are shaped by a plurality of series-type resonant branches. It allows to synthesize multi-band transfer functions with arbitrary order and number of passbands with inter-band TZs. A theoretical analysis of the proposed multi-passband filter scheme is expounded. Also, its potential for fully-reconfigurable multi-band bandpass filter realization through TZ reallocation is studied at the ideal-design level.

The paper presents proposal of a fully-differential (1 + α)-order low-pass filter. The order of the filter and its cut-off frequency can be controlled electronically. The filter is proposed using operational transconductance amplifiers (OTAs), adjustable current amplifiers (ACAs) and fully-differential current follower (FD-CF). The circuit structure is based on well-known Inverse Follow-the-Leader Feedback (IFLF) topology. Design correctness of the proposed filter is supported by PSpice simulations with transistor-level simulation models. The ability of the electronic control of the order has been tested for five individual values of parameter α. Furthermore, the ability of the electronic control of the cut-off frequency of the filter has been also tested for five different values. Additionally, the simulation results of the proposed fully-differential (F-D) filter are compared with the results of the single-ended (S-E) equivalent of the presented filter.DOI: http://dx.doi.org/10.5755/j01.eie.23.3.18332

A new half-mode frequency-tunable SIW (substrate-integrated waveguide) bandpass filter with a constant absolute bandwidth is presented in this paper. For achieving the constant bandwidth, we have developed new external and internal coupling structures capable of exhibiting specified coupling values over the frequency tuning range of the presented filter. Hence, the presented filter employs no tuning components in the coupling structures and this avoids the insertion loss increase due to tuning components. For verification, a second-order filter has been designed, fabricated, and measured. The filter has the insertion loss smaller than 2.0 dB over the frequency tuning range from 1.85 GHz to 2.3 GHz. The bandwidth slightly varies from 136 MHz to 142 MHz.

A hardware implementation of 3D pipelined Laplace filter has been presented in the paper. The filter is composed of rotation and delay unit structures with a help of CORDIC algorithm. Synthesis of the pipelined 3D Laplace filter is based on synthesis of 2D and ID filters. Proposed implementation of the filter has been compared to the implementation of the filter based on direct form. Parameters of both filter structures implemented in FPGA, have been measured and compared.

This paper presents a practical possibility of realization of a filter with simultaneous band-pass and low-pass characteristics within one simple, microstrip mixed circuit with lumped components. In particular, it was important to obtain an arbitrary, narrow-band microwave filter — BPF — with a fractional bandwidth of 10%, and a low-pass filter with favorable RF characteristics up to several hundred-MHz. The proposed simplified design method and transformations provide good theoretical and experimental results. One model of the distributed/lumped filter which confirms the theory as to the realization of the filter was designed and experimentally made.

This article studies a filter belonging to the category of bandpass filters. This filter has two resonators located on the substrate with dielectric conductivity e=4.4 and thickness h=1.5 mm. Resonators used in the bandpass filter (BPF) allowed for technologically realizable structures with smaller sizes as compared to standard structures. The electrodynamic simulation program was used in order to check the operability of the structure before its manufacturing. The filter central frequency is 7.5 GHz, and the working band is 1,000 MHz. After the filter was designed, a prototype was manufactured with the use of standard microstrip devices production techniques.

A transfer-function-adaptive quasi-elliptic-type microwave bandpass filter is presented. The devised fully-reconfigurable filter is based on a resonator-cascade structure with static impedance inverters and only exploits the tuning of its resonating nodes to achieve all its reconfiguration properties. They include center-frequency, bandwidth, and transmission-zero (TZ) control for bandpass-type responses, as well as the intrinsic switching-off — i.e., without RF switches — of the filter. Moreover, it features less in-band insertion-loss levels and improved linearity behavior — specially for narrow-band states — when compared to more-classic bandwidth-tunable filters that use inter-resonator coupling variation. The operational foundations of the engineered fully-reconfigurable filter architecture are theoretically expounded in a coupling-matrix framework. Besides, a tunable three-pole microstrip filter prototype in the range 1.2–1.7 GHz is developed and tested for experimental-demonstration purposes.

In this paper, we proposed a compact quad-band bandpass filter (BPF) using multilayer substrate technique. The filter is designed to have quad-band at 1.8, 2.4, 3.5 and 4.2 GHz. The four passbands are simultaneously generated by controlling the impedance and length ratios of the stub-loaded stepped impedance resonators (SIRs). By using the stub-loaded SIRs, the filter with closed passbands can be easily achieved. The frequency response of wide stopband is generated by using the defected ground structure (DGS) and having around −25 dB stopband from 4.2 to 12 GHz. The filter can provide the multi-path propagation to enhance the frequency response and achieving the compact circuit size. The measured results are in favorable agreement with the full-wave electromagnetic (EM) simulation results.

In this paper, we intend to design of a wide band dualband filter with dispersive couplings for improved selectivity. The proposed approach consists to use this novel filter synthesis technique, taking advantage of the frequency variation of coupling values, for generating additional transmission zeroes. The dispersive coupling behavior is demonstrated and employed to design a four pole filter with three transmission zeros. The design is validated by a prototype and a six-pole dual-band bandpass filter based on the same concept is proposed for 5G millimeter-wave bands.

This paper addresses the application of stub-loaded planar circuits to the realization of dual-band bandpass filters and extended-upper-stopband broad-band bandpass filters with quasi-elliptic transfer function. To this aim, different classes of homogeneous- and stepped-impedance parallel-type open-ended stubs are exploited. Analytical design formulas for the transmission zeros (TZs) generated by these stubs are provided. Furthermore, for experimental-validation purposes, two multipole microstrip prototypes are manufactured and characterized.

This paper presents a vertically-integrated second-order tunable planar filter/antenna that expands upon previous work with tunable filter/antennas. This work demonstrates the use of a radiating element as a resonator in the filter and uses mixed electric and magnetic coupling to achieve a constant absolute bandwidth over the filter tuning range without the need of additional tuning elements on the coupling structures. The device is tunable from 1.65 to 1.95 GHz with an absolute bandwidth of 52.03 ± 2.76 MHz and return loss above 15 dB over the tuning range. The measured gain is −0.52–5.72 dBi with cross-polarization level better than 15 dB.

The selection of reactive power compensation and higher harmonic filtration method for an exemplary industrial plant was presented in the paper. Based on measurements carried out on the real object, four solutions were proposed i.e. a passive filter, a modified passive filter and an active filter without and with a higher harmonic filter. For the proposed solutions the proper simulations were performed. The results of simulation with the corresponding description were presented. In the conclusions section the advantages and disadvantages of each proposed solution were summarized.