Interdigital Bandpass Filter Research Articles

Highly selective dual-band interdigital bandpass filter for C-band applications

Highly selective dual-band interdigital bandpass filter for C-band applications

A Miniaturized Wideband SIR Interdigital Bandpass Filter With High Performance Based on TSV Technology for W-Band Application

In this paper, an ultra-compact wideband stepped impedance resonators (SIR) interdigital bandpass filter (IBPF) is proposed based on through-silicon via (TSV) and three-dimensional integrated circuit (3D IC) technology. SIR structure can achieve higher coupling strength at a small impedance ratio. On this basis, the IBPF is designed by exploiting λ/4 SIR, the proposed filter is realized with compact size and far parasitic passband, and exhibits superior fractional bandwidth and out of band suppression characteristics. Based on the transformation of Chebyshev low-pass circuit model, a seventh-order IBPF centered at 98.5GHz is obtained. An improved method combining TSV technology with coupling coefficient method is proposed, which simplifies the design process and improves the influence of parasitic inductance on the design process. The fractional bandwidth (FBW) of SIR IBPF based on TSV is 40%, the insertion loss is less than 1.3dB, and a reflection of better than 30 dB in the passband. The size of the compact SIR IBPF is only 0.24×0.7mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (0.28 × 0.79 λg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ).

Compact 5G Nonuniform Transmission Line Interdigital Bandpass Filter for 5G/UWB Reconfigurable Antenna

In this study, at two different fifth generation (5G) low-frequency bands (3.7-4.2 GHz and 5.975-7.125 GHz) and based on nonuniform transmission lines (NTLs) theory, a compact three-quarter-wave resonators interdigital bandpass filter (IBPF) is analyzed, designed, and fabricated. The compact proposed filter is considered as a good candidate for reconfigurable 5G low-frequency bands and ultrawide band (UWB) antenna, which will reduce the size of the final RF communication system. Firstly, a uniform transmission line (UTL) IBPF at these two bands is designed and tested; then the NTL concept is applied for compactness. For both UTL and NTL IBPFs, different parametric studies are performed for optimization. At the first frequency band, size reductions of 16.88% and 16.83% are achieved in the first (symmetrical to the third resonator) and second λ/4 resonator of UTL IBPF, respectively, with up to 36.6% reduction in the total area. However, 16.46% and 16.33% size reductions are obtained in the first (symmetrical to the third resonator) and second λ/4 resonator, respectively, at the second frequency band with a 40.53% reduction in the whole circuit area. The performance of the proposed NTL IBPF is compared with the UTL IBPF. The measured reflection coefficient of the proposed NTL IBPF, S11, appears to be less than -10.53 dB and -11.27 dB through 3.7-4.25 GHz and 5.94-7.67 GHz, respectively. However, the transmission coefficient, S12 is around -0.86 dB and-1.7 dB at the center frequencies, fc = 3.98 GHz and 6.81 GHz, respectively. In this study, simulations are carried out using high-frequency structure simulator (HFSS) software based on the finite element method (FEM). The validity of the proposed theoretical schematic of this filter is proved by design simulations and measured results of its prototype.

Annular shape interdigital filter with increased frequency selection design

The design of the interdigital bandpass filter of annular shape with increased frequency selectivity due to the convergence of the input and output lines and introduction of additional lines between them is suggested. This allows the amplitude-frequency characteristic of such a filter to be formed with attenuation poles on the edges of its bandpass, which significantly increases the steepness of its slopes. A model of such four-resonator interdigital filter is made and the results of its experimental investigations are given. They showed that the developed filter can be successfully used in measuring channels to determine the frequency of signals in modern microwave equipment for communication, radar and telecommunications.

An Inter digital- Poison Ivy Leaf Shaped Filtenna with Multiple Defects in Ground for S-Band bandwidth Applications

The proposed work, a filtenna for s band application is implemented. It is designed by embedding an Interdigital band pass filter (IDBPF) and leaf shaped antenna which are operated in S band. The IDFBPF is having seven resonators with one end shorted through dual vias. It offers a bandwidth of 1.3GHz from 1.65GHz to 2.95GHz. A Dumbbell shaped DGS (Defected Ground Structure) provided in ground to improve the filter characteristics. Measured pass (BRL) band return loss (S11) &amp; insertion loss (S12) are -18dB &amp; -4.6dB correspondingly. Further, leaf shaped antenna is designed based on modified polar transformation equation; it has 2.7 GHz bandwidth from 1.3 GH to 3 GHz and has a gain of -5.45dBi, and return loss (S11) of -19.5 dB. The filtenna is obtained by integrating the IDBBPF in the fodder line of the leaf designed antenna. The final model has 1.2 GHz operating bandwidth from 02.30 GHz to 03.50 GHz with peak arrival damages at 2.4GHz and 3.1GHz with -20dB and-24dB respectively. The designed filtenna has a pass band gain of -5.3dBi. The shift in operating band is due to combining the filter with antenna. The proposed model is invented on FR4 substrate having a wideness of 01.60 mm and having a dimension of 0.25 0.58 ?02. In this final model two complementary slip ring resonators (CSRR) are used in addition with four dumbbell structures as defects in the ground plane to avoid ripples in return loss (S11) graph. A high degree of concordance exists between empirically measured and simulated outcomes. The radiation band is showing its application in S band wireless mobile communications, Wi-Fi and ISM 2.4GHz band.

Compact Interdigital Bandpass Filter, Diplexer, and Triplexer Based on Through Quartz Vias (TQVs)

An interdigital bandpass filter (BPF), diplexer, and triplexer are proposed based on the through-quartz via (TQV) technology in this article. TQVs are inserted between adjacent resonators to adjust the coupling coefficients, resulting in the reduction in the total area of the filter. Equivalent lumped circuit of the filter is researched. The proposed BPF operates at 28.56 GHz, and the 3-dB fractional bandwidth (FBW) achieves 10%. The out-of-band rejection is better than 20 dB with frequencies up to 2.59 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0}$ </tex-math></inline-formula> . Based on the proposed filter, interdigital diplexer operating at 28.85 and 37.18 GHz, respectively, is constructed, which exhibits an isolation better than 30 dB and a stopband up to 2.61 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{1}$ </tex-math></inline-formula> of the lower channel. The triplexer operating at 22.24, 29.6, and 36.46 GHz is also designed in this article, which exhibits a wide stopband up to 2.96 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{3}$ </tex-math></inline-formula> of the lower channel with lower insertion loss. Measurement results agree well with the simulations over the whole band.

HilbertNet: A Probabilistic Machine Learning Framework for Frequency Response Extrapolation of Electromagnetic Structures

In this article, we propose a probabilistic machine learning framework for extrapolating the frequency response of distributed physical circuits. For the structures where there is hidden dependency between higher and lower frequency features, we propose a method to extrapolate the response while providing confidence intervals harnessing Bayesian recurrent neural networks (RNN) thereby avoiding extensive simulations and saving computational time. To address complex-valued impedance, Hilbert transform is used to relate the real and imaginary parts where a Hilbert-based RNN architecture is proposed called Hilbert Net to extrapolate the frequency response. We apply the technique to four applications: 1) A simple microstrip transmission line circuit for proof of concept, 2) coupled waveguide filter operating in D-band comparing with measured results, 3) fifth-order interdigital bandpass filter for 28 GHz band, and 4) complex stack-up power delivery network (PDN) having a sharply changing response to test the framework limits. Results show that our architecture performs accurate extrapolation with a normalized mean square error of 0.008 squared with 95% confidence for a typical PDN. Using probabilistic networks, we achieve a tight confidence bound on our results. Furthermore, the reliability of Hilbert Net is assessed as to how far the response can be extrapolated.

Compact Size of an Interdigital Band-Pass Filter with Flexible Bandwidth and Low Insertion-Loss Using a Folded Spiral and Stepped Impedance Resonant Structure

A conventional interdigital bandpass filter (BPF) is characterized by coupled and tapped lines and affords low insertion loss (IL) and easy fractional bandwidth (FBW) adjustment. However, the maximum FBW of the filter is limited to 30%, beyond that, its gap size increases, thereby rendering filter fabrication impractical on a standard printed circuit board. In addition, the filter size cannot be changed because it dictates the operational frequency of the filter. Hence, in this study, we propose a compact interdigital BPF based on a spiral and folded stepped impedance resonator (SIR), which affords low IL and excellent group delay. The spiral, folded structure facilitates drastic FBW adjustment: the center frequency and adjustable range of the FBW of the designed BPF are 800 MHz and 80 to 180%, respectively. Additionally, the proposed BPF can adjust the FBW by k-factor which can adjust from 80 to 180%. The insertion and return losses of the proposed filter are 0.043 dB and 17.1 dB, respectively, and the group delay is 0.098 ns. The total filter size is only 13.8 mm × 5.98 mm, which corresponds to a size reduction by factors of &gt;2/8 relative to a conventional filter and 2.1 relative to the latest BPF design. The group delay difference between the BPF and other filters is 0.15 ns. In addition, the range of adjustable FBW for the filter is 1.36 times different than for other filters.

5G Hairpin and Interdigital Bandpass Filters

At two low 5G frequency bands: 3.7 GHz - 4.2 GHz and 5.975 GHz -7.125 GHz, Hairpin Bandpass Filter (HPBF) and Interdigital Bandpass Filter (IBF) are designed and simulated in this paper. Both filters show good results in terms of matching and transmission responses with a wide bandwidth through the two frequency bands. HPBF with simple design resulted in good return and insertion losses, < - 10.43 dB and - 0.63 dB, and < -14.48 dB and -0.46 dB through frequency bands: 3.51 GHz - 4.27 GHz and 5.58 GHz - 7.24 GHz, respectively. In addition to good filter response that IBF provides, it supports high order second harmonics suppression. The simulated S11 and S12 of this filter are < -11.15 dB and -0.63 dB with out of band rejection up to 11.12 GHz through the frequency band 3.56 GHz - 4.25 GHz. Furthermore, at the second frequency band IBF is designed with two different grounding via hole radii (rVia), case 1: rVia = 0.4 mm and case 2: rVia = 0.7 mm. For both cases, the designed filter shows good results with high order second harmonics suppression up to 18.33 GHz and 18.96 GHz. In this paper, High Frequency Structure Simulator (HFSS) software is used to carry out the simulation.

Compact design of diplexer for base stations operating within frequency bands 2.3–2.4/2.49–2.69 GHz

A new compact design of diplexer with high electrical performances is proposed for base station antennas operating within frequency bands 2.3–2.4/2.49–2.69 GHz. The diplexer consists of two interdigital band-pass filters and coaxial power divider. Proposed design has high potential from view poin of implementation of wide-band as well as medium and narrow bands filters. The fabricated diplexer shows the following measured characteristics: reflection coefficient is -18 dB within passbands, insertion loss is -0.28 dB, isolation of ports is -30 dB. Diplexer has the relatively simple easy to manufacture design and compact dimensions, so it may be directly integrated into the base station antennas.

Integrated design of filtering antenna with high selectivity and improved performance for L-band applications

An integrated design of compact filtering antenna having high selectivity and suppressed unwanted harmonics is proposed in this paper. The proposed filtering antenna is obtained by integrating a modified elliptic-shaped monopole antenna with a modified interdigital bandpass filter (IBPF). At first, a modified elliptic-shaped monopole antenna is designed and investigated through numerical simulation and experimentally. Further, the modified IBPF reported in the literature is integrated with the proposed monopole antenna to achieve good passband selectivity and suppressed unwanted harmonics for the proposed filtering antenna. The proposed filtering antenna is analysed through numerical simulation software. The simulated −10 dB reflection coefficient bandwidth of the proposed filtering antenna covers the frequency range 1.01–1.96 GHz with improved band-edge selectivity and unwanted harmonic suppression up to 8 GHz (= 5.4 f0, where f0 is the centre frequency of passband). It has nearly stable omnidirectional radiation patterns over the whole frequency band. The proposed filtering antenna was fabricated and experimentally tested. The experimental results are nearly in agreement with corresponding numerical simulation results. The proposed filtering antenna can be a suitable candidate for various L-band wireless communication applications.

Inkjet-Printed Interdigital Bandpass Filter with Wide Stopband Using Multilayer Liquid Crystal Polymer Technique

This article presents a two-layer inkjet-printed interdigital bandpass filter using lamination bonding process on liquid crystal polymer (LCP) substrates for radio frequency electronic applications. Various percentages of torque force were applied over a 4 × 4 cm2 area with a 942 kg fixed force in the lamination bonding process. The insertion loss and surface morphology of the inkjet-printed silver film were examined on various torque forces to develop the lamination bonding process. The lamination bonding was performed at 12% torque and 270°C. A three-dimensional bandpass filter was realized with a S21 of −2.2 dB at 11.5 GHz with a 17% fractional bandwidth. A multilayer inkjet-printed bandpass filter was successfully developed to verify the design methodology and fabrication of inkjet-printing technology and lamination bonding technique for a three-dimensional integrated circuit package.

Investigation on compact modified wideband interdigital bandpass filter with wide stopband using spurlines and defected ground structures

ABSTRACTIn this paper, a compact modified microstrip interdigital bandpass filter (IBPF) having two pairs of spurlines and a pair of defected ground structures (DGS) containing stepped impedance resonators (SIRs) is described for L–Band receiver applications. A combination of spurlines and SIR‐shaped DGS is used to obtain the proposed compact IBPF with wide stop‐ and pass‐bands. The reduction in size and wide stopband characteristic of the filter result from band notched characteristic of spurline, and harmonic suppression along with miniaturization characteristic of DGS. The equivalent circuit parameters of the spurlines and DGS are also extracted and their values are computed. The proposed compact filter is of size 0.24λg × 0.34λg (0.107λ0 × 0.075λ0), where , λ0 is the free space wavelength at the centre frequency (f0) of 1.47 GHz and (=10.2) is the dielectric constant of the substrate. The simulated and measured 3‐dB fractional bandwidths of the proposed filter are 80% (over the frequency range 0.89 −2.05 GHz) and 79% (over the frequency range 0.87–2.01 GHz) respectively. The proposed BPF has stopband attenuation better than 17 dB upto a frequency of approximately six times the centre frequency of the desired passband. For the validation of the simulated results, the prototype of the proposed filter was fabricated and its parameters like S–parameters, group delay and phase responses were measured. The experimental results for the proposed BPF are nearly in agreement with the respective simulation results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2634–2639, 2016

小型化交指型LTCC带通滤波器设计

本文提出了一种基于LTCC技术的小型化交指型带通滤波器的设计方法，通过在交指线末端加载对地电容，压缩了谐振器尺寸，将对地电容布置在分立的空间中，避免了电容间的耦合干扰，引入非相邻谐振器间交叉耦合，在通带两端各产生一个零点，提高了边带抑制。设计了一款中心频率2.3 GHz，带宽200 M交指型带通滤波器，插损小于2.5 dB，通带波动优于0.5 dB，利用三维仿真软件HFSS建模及优化，并利用LTCC工艺加工制造，尺寸仅为3 mm × 2 mm × 1.5 mm，经测试，实际测试曲线与仿真曲线符合较好，验证了设计的有效性。 A method of designing miniaturized interdigital bandpass filter based on LTCC technology was proposed, through loading ground capacitance at the end of interdigital transmission line, com-pressed the volume of resonator, to arrange the ground capacitance in discrete space, avoided the coupling interference between themselves, then cross-coupling was introduced between nonad-jacent resonator, generated two transmission zeros on both sides of the passband and improved the sideband suppression. A interdigital bandpass filter with center frequency 2.3 GHz and bandwidth 200 M was designed, the insertion loss was less than 2.5 dB, passband fluctuation was better than 0.5 dB, HFSS was used to construct the 3D model and optimize the simulated results, then fa-bricated the filter with LTCC technology, the size was only 3 mm × 2 mm × 1.5 mm, the measured curves confirmed well with the simulated curves, verified the validity of the design.

X‐band flexible bandpass filter based on ultra‐thin liquid crystal polymer substrate

The performance of an X-band flexible band-filter on ultra-thin liquid crystal polymer (LCP) substrate is investigated. The 50 µm-thick LCP substrate is adopted to enhance the flexibility of circuits. For the purpose of fabrication by the conventional printed circuit board process, copper-clad laminate with 18 µm thickness is selected. Excellent microwave transmission characterisation is demonstrated by measuring the microstrip line at flat and bending conditions. An X-band interdigital bandpass filter based on a half-wavelength microstrip line resonator is designed and fabricated for purpose of demonstration. The measured results at the flat condition show that the insertion loss is 2.1 dB at centre frequency of 9.4 GHz and the return loss is better than 20 dB at the designed band. The performance at the bending condition shows that the bending effect causes little deterioration to the performance at a different bending radius.

SIW‐based interdigital bandpass filter with harmonic suppression

ABSTRACTA novel configuration of interdigital bandpass filter based on the substrate integrated waveguide (SIW) technology is proposed. In addition to the interdigital resonators in SIW that determine the main response/characteristics of the filter, narrowing the width of the SIW at the center of the filter and additional vias at its input and output parts act as two additional control mechanisms to achieve the desired filter response. Moreover, dumbbells are etched to the ground side of the microstrip feeding sections at both ends of the filter to improve its harmonic suppression. A prototype filter is designed and fabricated for verification. The measured results are in good agreement with the simulations, and the filter exhibits very good harmonic suppression. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:66–69, 2015

Novel Compact Interdigital Bandpass Filters with Multilayer Stepped Impedance Resonators/Folded Quarter–Wavelength Resonators

Novel compact interdigital bandpass filters (BPFs) which used multilayer stepped impedance resonators (SIRs)/folded quarter–wavelength resonators were presented. Two measures were taken to reduce the sizes of the proposed filters. Firstly, two resonators (SIRs and folded quarter–wavelength resonators) with novel structures were designed. Secondly, all the designed resonators were located on different dielectric layers. The proposed interdigital BPFs, which were simulated with the high frequency structure simulator (HFSS), show excellent performance and could realize the miniaturization purpose. Furthermore, it is found that the proposed filter with folded quarter–wavelength resonators is more excellent in realizing miniaturization and improving performance than that with SIRs.

Miniaturization of Embedded Bandpass Filter in LTCC Multilayer Substrate for WiMAX Applications

A compact radio frequency (RF) bandpass filter (BPF) in low temperature co-fired ceramic (LTCC) is suggested for WiMAX applications. The center frequency (<TEX>$f_0$</TEX>) of the BPF is 5.5 GHz and its pass band or 3-dB bandwidth is 700 MHz to cover all the three major bands, low and middle unlicensed national information infrastructure (U-NII; 5.15-5.35 GHz), World Radiocommunication Conference (5.47-5.725 GHz), and upper U-NII/industrial, scientific, and medical (ISM) (5.725-5.85 GHz), for the WiMAX frequency band. A lumped circuit element design-the 5th order capacitively coupled Chebyshev BPF topology-is adopted. In order to design a compact RF BPF, a very thin (<TEX>$43.18{\mu}m$</TEX>) ceramic layer is used in LTCC substrate. An interdigital BPF is also designed in silicon substrate to compare the size and performance of the lumped circuit element BPF. Due to the high relative dielectric constant (<TEX>${\varepsilon}_r$</TEX> = 11.9) of the silicon substrate, the quarter-wavelength resonator of the interdigital BPF can be reduced. In comparison to the 5th order interdigital BPF at <TEX>$f_0$</TEX> = 5.5 GHz, the lumped element design is 24% smaller in volume and has 17 and 7 dB better attenuation characteristics at <TEX>$f_0{\pm}0.75$</TEX> GHz.

Spurious Response Suppression in Microstrip Bandpass Filters Using Defected Microstrip Structures

A new technique for suppressing the spurious passband of microstrip bandpass filters using defected microstrip structures is presented. This new defected microstrip structure resonator is realized by etching an open ring in the microstrip line. Due to its bandstop nature, the defected microstrip structure resonator can be used in microstrip bandpass filters to eliminate the spurious response. A detailed, fast, and accurate analysis using multiconductor transmission lines, and the method of lines is introduced to design the defected microstrip structure structure. The great advantage of the proposed technique is that the design procedure of the filter does not differ from its conventional counterpart; also, the transmission zeros can be allocated to suppress any unwanted passband. To demonstrate the versatility of the proposed method, simulated and measured results for two typical coupled-line and interdigital bandpass filters are presented. The results reveal that the defected microstrip structure integrated bandpass filters can provide a rejection level exceeding 35 dB in the first spurious passband.

Design of Dual-Band Interdigital Bandpass Filters Using Both Series and Shunt Resonators

In this letter, we present a simple design method for dual-band bandpass filters (BPFs) with two independently controllable bandwidths. The proposed design is based on hybrid resonators which have both series and shunt resonances. For compact size, an interdigital BPF type is utilized. The simple design procedures are established based on an equivalent lumped circuit of the proposed dual-band BPF. Moreover, the proposed BPF has good skirt characteristics through transmission zeros created by the series resonance in the hybrid resonator and the cross-coupling. The third-order dual-band BPF is designed at center frequencies of 1.85 and 2.85 GHz with fractional bandwidths of 11% and 7.3%.