Multilayer bandstop filter for ultra wideband systems

A multilayer broadside-coupled microstrip-slot-microstrip structure is used to design a bandstop filter with a wide passband for ultra wideband (UWB) applications. The design procedure for the proposed filter is based on the conformal mapping technique and the even- and odd-mode analysis. The theoretical analysis indicates that value of the coupling factor between the top and bottom layers of the structure can be used to control the width of the stopband, whereas centre of that band can be controlled by the length of the coupled structure. To limit the passband of the proposed bandstop filter to 3.1 ?10.6 GHz, which is the specified bandwidth for UWB systems, a broadside-coupled bandpass filter is integrated with the proposed device. The simulated and measured results show that the proposed device achieve ,0.5 dB insertion loss across most of the passband and .20 dB insertion loss at the stopband. The device also shows a flat group delay across the passband with ,0.15 ns peak-to-peak variation. Hence, it is a suitable choice for the UWB systems that require a distortionless operation.     

Miniature coaxial resonator and related bandpass filter with ultra-wide stopband

Resonator of a new type is described, which is formed by two coaxial conductors applied onto the internal and external surfaces of a ceramic tube arranged in a metal case. An equation for the resonant frequencies is derived. In comparison to a standard coaxial quarter-wave resonator, the proposed device has a shorter length and manifold increased ratio of frequencies of the second resonance to the first resonance. The new resonator can be used for the creation of bandpass filters with ultra-wide stopband. The frequency response of a working prototype four-resonator filter is presented, in which the stopband at a −90 dB level extends up to a frequency that is 47 times greater than the central frequency of the passband.     

基于EBG结构的基片集成波导超宽带带通滤波器

为拓展带通滤波器的通带带宽,设计了一种基于EBG结构的基片集成波导（SIW）超宽带带通滤波器．该滤波器利用箭头形电磁带隙结构的阻波特性,将不同大小箭头形结构单元蚀刻在SIW上金属面,以获得超宽带通带．所设计的滤波器中心频率在985 GHz,相对带宽为3959%,通带内的最大插入损耗约为154 dB,相比于类似结构的带通滤波器,其带内回波损耗较大,且整体电路面积较小．测量结果与仿真结果基本吻合,有效地验证了该设计方法的有效性．     

一种基于SIFW的小型化宽带带通滤波器

为实现射频系统的小型化,本文设计出一种基于基片集成折叠波导( Substrate integrated folded waveguide,简称SIFW)的小型化宽带带通滤波器,并给出了仿真结果.为了改善带外抑制,滤波器通过交叉耦合,在通带低端引入两个传输零点.为改善通带高端滤波特性,在顶层和底层金属微带上刻蚀互补型开口谐振环(Complementary Split Ring Resonators,简称CSRR).仿真结果表明,所实现的滤波器中心频率在7.1 GHz,相对带宽约为47％,通带内回波损耗优于-15dB,插入损耗小于0.7dB.     

Compact double-mode cross-coupled microstrip bandpass filter with tunable transmission zeros

A compact double-mode cross-coupled microstrip bandpass filter with an asymmetric frequency characteristic and three transmission zeros is presented. The bandpass filter consists of a cross-coupled gap and a double-mode resonator of a half-wavelength line with a shunt-stepped-impedance open stub. In comparison to the conventional square loop dual-mode resonator, the proposed double-mode resonator achieves a 59% size reduction. The parametric studies on the electrical length of the open stub and the capacitance of the cross-coupling are provided in order to gain a better insight into the transmission poles and zeros. Then, a bandpass filter is designed, fabricated and tested to validate the design concept. From 2.3 to 2.5 GHz, the return loss is better than 10 dB and the insertion loss is <1.5 dB. There are three transmission zeros in the upper stopband at 2.8, 3.4 and 4.9 GHz.     

Compact quasi-elliptic microstrip bandpass filter using terminated anti-parallel coupled-line

A compact quasi-elliptic microstrip bandpass filter with lower and upper stopband zeros is presented. The bandpass filter consists of terminated anti-parallel coupled-line and the stopband zero is generated and controlled by the reactive termination. In comparison to the traditional parallel coupled-line bandpass filter, the proposed filter achieves simultaneous size reduction and sharp filter skirt. The usefulness of the proposed filter is validated by a simultaneously miniature and selective quasi-elliptic bandpass filter centred at 2.4 GHz with 4.6% fractional bandwidth as well as two transmission zeros at 2 and 3.2 GHz.     

Infinite impulse response microwave photonic filter using a dual drive modulator with an optoelectronic feedback loop

A novel design of a microwave photonic filter with infinite impulse response is demonstrated. The design is based on a dual drive modulator with an optoelectronic feedback loop. The stopband of the filter can be switched to passband and vice versa by switching the bias point of the dual drive modulator. Measured results confirm the theoretical expressions and demonstrate a rejection ratio and frequency selectivity which is greater than 30 dB.     

Spurious suppression of a microstrip bandpass filter using three types of rectangular PBG loops.

A novel microstrip bandpass filter with three types of rectangular, photonic bandgap (PBG) loops on a middle layer was designed and demonstrated using a full-wave electromagnetic (EM) simulator, with the predicted results verified by experiment. This investigation presents the configurations of conventional parallel-coupled 2 GHz filters with and without a PBG. The middle-layer of PBG loops adds an extra stopband-rejection mode to filter stopband; and it provides attenuation in excess of 25 dB at the second, third, and fourth harmonics, thus demonstrating that superior stopband characteristics at high frequency can be obtained using the proposed PBG loops in microwave filters.     

Modular two-dimensional analysis of SAW filters. II. Analysis and compensation results

For pt.I see ibid vol.39, no.1, pp.61-72 (1992). Physical effects causing distortions of the transfer function of a broadband (36% fractional bandwidth) spectrum shaping filter for digital radio with 16 quadrature amplitude modulation (QAM) are analyzed separately and connected with the modular two-dimensional (2-D) model described in Part I, demonstrating the importance of every single effect. A compensation of the second-order effects is performed, yielding an agreement between simulation and measurement in amplitude and phase of more than +/-0.1 dB and +/-1 degrees all over the passband. The stopband is also predicted with high accuracy.     

Low insertion loss, wideband bandpass filters with sharp rejection characteristics

A general circuit configuration using two transmission-line sections is presented to design a sharp-rejection bandpass filter. Sharp rejection characteristic is obtained by creating two transmission zeros across the filter passband by interfering signals propagating through the transmission lines. A simple lossless transmission-line model is used for filter analysis. If an impedance variation of 20-130 ? is considered, the present method is most suitable for 10-50% 3-dB fractional bandwidth variation. Two prototype bandpass filters having approximately 29% fractional bandwidth at the midband frequency 2.9 GHz are fabricated in microstrip line. The filter structures are simple and easy to fabricate. Theoretical, simulated and measured results are in good agreement.     

Ultra-wideband bandpass filters with improved out-of-band behaviour via embedded electromagnetic-bandgap

A class of ultra-wideband microstrip-line bandpass filters with improved out-of-band behaviours is presented by using an electromagnetic (EM) bandgap embedded multimode resonator. At first, the two EM bandgap structures are constructed by periodically loading uniform or non-uniform open-circuited stubs. Their performances are numerically characterised, aiming at exhibiting the existence of a bandstop in a frequency range of 15.0?30.0 GHz. These bandgap structures are then internally embedded in the middle part of an open-ended microstrip line resonator, constituting a modified type of multimode resonator. In the design, the dimensions of this resonator need to be properly adjusted towards allocating the first three resonant modes in the 3.1?10.6 GHz ultra-wide passband. To achieve a preferably wide upper stopband, the transmission zero of parallel-coupled lines is used to cancel the spurious fourth-order resonant mode. Also, higher-order modes in the upper band are inhibited by the employed bandgap structures. Two bandpass filters using the nonuniform stub-loaded resonator are finally designed, fabricated and tested. Predicted insertion/return losses and group delays are experimentally confirmed in a wide frequency range of 1.0?30.0 GHz.     

A novel broadband terahertz filter for photonic crystal

Abstract

The influence of the change of the radius of point defect cylinders, scattering dielectric cylinders, dielectric cylinders on both sides of line waveguide on S parameter is studied. According to the resonant coupling principle between micro-cavity and waveguide, a novel broadband terahertz filter is designed. The novel filter is formed by introducing scattering dielectric cylinders into the resonant microcavity, and the point defect cylinders are composed of HgTe material and adjusting the radius of dielectric cylinders on both sides of line waveguide. Results show that the 3 dB bandwidth reaches 74.2 GHz, the return loss is less than ?12.02 dB, the maximum insertion loss in-band reaches 0.35 dB and its drop efficiency is up to 96.79%. The novel terahertz filter has flat passband, sharp rejections at out-bands and its central frequency is 0.338THz. The good performances show that it can meet the requirements of high speed and broadband in terahertz atmosphere communication I window.     

Synthesis of ultra-wideband bandpass filter employing parallel-coupled stepped-impedance resonators

To design an ultra-wideband (UWB) bandpass filter with the fractional bandwidth (FBW) up to 110% (3.1%10.6%GHz), a new filter prototype consisting of multi-stage parallel-coupled stepped-impedance resonators (SIRs) is synthesised based on the transmission-line theory rather than the conventional multi-mode property. Asymmetrical SIRs are employed instead of the conventional symmetrical/quasi-symmetrical ones, so that an extra degree of freedom is introduced in circuit parameter selection. As a result, the minimum dimension of the coupling gaps between the adjacent SIRs is successfully enlarged to be more than 0.1%mm, which alleviates the requirement on fabrication precision. A simple equivalent circuit for this filter prototype is represented in the form of distributed parameters and the corresponding Chebyshev filtering function is derived as well. The relation between the number of poles in passband, N _p, and the stage of the filter, n, is summarised to be N _p=3n+2. To validate the newly derived synthesis theory, a one-stage UWB filter is first synthesised to compare with the previously published results obtained by the electromagnetic (EM) simulator. Furthermore, a two-stage filter is synthesised to successfully meet the Federal Communications Commission (FCC)+s indoor/outdoor spectrum specifications. The fabricated UWB filter exhibits a compact size of 26.58+mm in total length, low insertion loss (0.9+dB at 6.85+GHz), flat group delay (0.5+0.1+ns), good stopband characteristics (+S21+++40+dB at 1+2+GHz) and steep skirt property (+28+dB/GHz) as well. It should be noted that the proposed filter prototype can be also used to realise aUWB filter with an FBW even greater than 110+.     

Optimal design of an RSPUDT-based SAW filter with constant group delay

This paper describes the application of resonant single-phase unidirectional transducers (RSPUDTs) to the development of low-loss SAW filters with constant group delay in transition bands as well as in the passband. A low-loss SAW filter with constant group delay was designed and fabricated on a 128 degrees YX-LiNbO3 substrate. Experimental results were in good agreement with the design; the group delay deviation of 20 ns was realized over the range of +/-8 MHz at the center frequency of 512 MHz. The minimum insertion loss and -3 dB bandwidth were 4.3 dB and 8.5 MHz, respectively. The application of this technique is also extended to develop high-performance wideband filters employing quasi-slanted interdigital transducers.     

Widely tunable optical bandpass filter by use of polymer long-period waveguide gratings

We report the design and fabrication of a widely tunable optical bandpass filter based on using two identical long-period gratings formed along a polymer channel waveguide with a section of the waveguide core removed. The peak transmission of the passband of the fabricated filter is approximately 60% and the bandwidth of the passband is approximately 6 nm. The filter is thermally tunable over the C + L band (1520-1610 nm) for both TE and TM polarizations with a temperature control of approximately 30 degrees C.     

基于SIR的同轴腔体带通滤波器设计

基于阶跃阻抗谐振器SIR(stepped impedance resonators)的基本原理,采用λg/4型SIR作为基本谐振单元,设计了一款小型化同轴腔体带通滤波器.仿真结果显示,相比实际长度λg/4该滤波器尺寸压缩了56.7%,通带内回波损耗小于-17.5 dB,插入损耗小于0.1 dB,带外抑制度达到了-38.8 dB,满足了现代通信系统对滤波器小型化、低插入损耗、高选择性的要求,能够广泛应用于现代移动通信系统.     

Multi-passband bandpass filters with low-temperature co-fired ceramic technology

The bandpass filters with multiple passbands have been proposed. To achieve multiple passbands, transmission lines shunted with short-circuit transmission lines are adopted. Moreover, the bandwidth of each passband can be controlled by properly choosing impedances and electrical lengths of the transmission lines and short-circuit transmission lines shunted. The design procedures of the proposed multi-passband filter are also described here. Finally, the agreement between the measured results and theoretical predictions sufficiently validates the proposed design and filter configuration.     

Spurious suppression of a microstrip filter using three types of rectangular PBG loops

A novel microstrip bandpass filter with three types of rectangular, photonic bandgap (PBG) loops on a middle layer was designed and demonstrated using a full-wave electromagnetic (EM) simulator, with the predicted results verified by experiment. This investigation presents the configurations of conventional parallel-coupled 2 GHz filters with arid without a PBG. The middle-layer of PBG loops adds an extra stopband-rejection mode to filter stop-band; and it provides attenuation in excess of 25 dB at the second, third, and fourth harmonics, thus demonstrating that superior stopband characteristics at high frequency can be obtained using the proposed PBG loops in microwave filters.     

A novel reflector-filter using a SAW waveguide directional coupler

The SAW waveguide technique was used to form a novel reflector-filter for the realization of compact IF filters in CDMA handsets. The reflector-filter design is an attractive technique to obtain characteristics with steep skirts in a short device length, because the SAW propagation path is folded and the frequency response is synthesized by utilizing both IDT and reflector responses. In this paper, we propose a new reflector-filter structure using a SAW waveguide directional coupler. For the implementation of the proposed reflector-filter, the key technology is the design of SAW waveguides. We have formed SAW waveguides using Al gratings loaded on the surface of the substrate. The pitch of the Al gratings has been chosen unequal to half the acoustical wavelength to avoid the occurrence of the gratings stopband at the filters passband position. Using the proposed reflector-filter structure, PCS-CDMA IF filters were fabricated on quartz substrates. The filter exhibited an insertion loss of 8.5 dB, a 5 dB bandwidth of 1.45 MHz, and a rejection of more than 33 dB at the center frequency +/-1.25 MHz with the package size of 4.8x9.1 mm (2). i.e., half the size of a conventional transversal filter was achieved using the proposed reflector-filter technique.     

1.5-GHz high-T c superconducting microstrip bandpass filter of miniaturized configuration

A 1.5-GHz four-stage microstrip bandpass filter was designed with the miniaturized hairpin resonator structure to reduce the configuration in size. The filter was fabricated using high-T _c superconducting films on a 12 × 12 mm² LaAlO₃ substrate. The passband insertion loss of the filter was measured to be -0.4 dB at 77 K, while it was estimated by a planar electromagnetic simulator to around -19 dB when gold films are used instead of the superconducting films.