半圆环形双模带通滤波器的设计

本文提出一种由一个半圆环形谐振器和一个T型微扰构成的新型微带双模滤波器,T型微扰具有两个可调参数,增加了调整双模的自由度.合理设置输入和输出馈线之间的耦合结构,可以在双模滤波器通带两侧产生两个传输零点,从而改善滤波器的选择性.为了验证提出结构的正确性,设计了一个中心频率为2.4GHz双模带通滤波器.仿真结果表明:该滤波器具有10.5%的相对带宽,通带内插入损耗小于0.32dB,且带外衰减大于20dB.     

一种基于LTCC的新型边带陡峭的带通滤波器的设计与实现

提出了一种基于LTCC的新型边带陡峭的带通滤波器的设计与实现方法。该带通滤波器电路采用六级结构紧凑的梳状线谐振单元,并创造性的将谐振单元连接起来,替代了原先的谐振单元间的宽边耦合,有效的增大了工作带宽,增强了边带抑制。本文设计的六级带通滤波器的性能指标如下:中心频率为4.65GHz,带宽为1.2GHz,通带内插入损耗小于2.5dB,回波损耗优于-15dB,带外1GHz处的衰减优于35dB。本滤波器通过LTCC技术进行加工生产,实物测试结果与软件仿真结果吻合较好。     

一种基于LTCC的小型化吸收式带通滤波器的设计

提出了一种基于LTCC技术的新型小型化吸收式带通滤波器的实现方法。该吸收式滤波器基于耦合相消原理由两个四阶梳状线带通滤波器和两个3dB正交定向耦合器组成。为了减小实物体积,梳状线带通滤波器采用三层短路耦合线结构,耦合器采用两层蛇形宽边耦合带状线结构,并且上下放置两个梳状线带通滤波器。运用三维电磁仿真软件HFSS建模仿真,设计了一款吸收频带范围为2GHz～4GHz,滤波频带范围为2.85GHz～3.25GHz的吸收式带通滤波器,通带内插入损耗小于2dB,各端口驻波比优于1.4,在低阻带0GHz～2.55GHz和高阻带3.55GHz～5GHz内的衰减均大于30dB,体积仅为8.4mm×5mm×2.5mm。测试结果与HFSS仿真结果较为吻合。     

2GHz宽阻带低噪声放大器的协同设计

去除了低噪声放大器(LNA)与带通滤波器之间的50 Ω的匹配界面.用带通滤波器代替低噪声放大器的输出匹配网络,将二者进行协同设计.采用的滤波器具有宽阻带.能够直接滤除二次谐波.仿真结果表明,协同设计后,LNA的稳定性得到了有效的改善,在整个频段内达到了绝对稳定;在中心频率2 GHz处,增益为14.593 dB,噪声系数为2.668 dB;谐波抑制效果也很明显,二次谐波处S21为-71.140 dB.     

双通带带通滤波器的分析与设计

基于方型环与开路线相结合的结构设计了一种新型微带双通带带通滤波器.该滤波器通过调节方型环与开路线的尺寸分别获得两个通带.经仿真优化,并制作了实物模型.测试结果表明该滤波器能够工作在2.365 GHz和4.465 GHz,插入损耗都小于3 dB.测量结果与仿真曲线一致性较好.该滤波器结构简单、设计方便、体积小、易于加工,便于与其它电路集成,可以广泛应用于射频前端.     

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.     

高介电常数微波介质陶瓷的研制及其同轴型滤波器的仿真

本文研制了一种由双镧系元素组成的BaO-Ln2O3-TiO2(BLT)系高介电常数、低损耗材料,并以该材料为基础,设计并研究了其独石型同轴滤波器。滤波器采用新颖的凹槽式电感耦合和一端金属面短路的λ/4结构。利用HFSS高频仿真软件对该滤波器的传输特性进行了仿真,表明其具有中心频率为1.83GHz、带宽43MHz、插入损耗小于0.5dB、带内纹波为1.5dB的优异的通带特     

G形DMS结构高选择性低通滤波器的分析与设计

提出一种新颖的G形缺陷微带结构(DMS)微带线,以G形DMS为结构单元,设计并实现了一种具有高选择性和宽阻带特性的微带低通滤波器.与传统的DMS结构相比,G形DMS具有更低的谐振频率和更宽的阻带抑制.对设计的滤波器进行了测试,实测结果表明:该滤波器3dB截止频率为3.17GHz,频率选择性达189dB/GHz,同时在3.4GHz ～ 10GHz阻带内抑制度大于25dB,有效地抑制了二次和三次谐波.该滤波器占用大小仅为26mm×15mm,实测结果与仿真良好吻合,表明了该DMS的有效性及实用性.     

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．     

基于双频谐振器的小型化双频滤波器设计

本文提出一种设计小型化、低损耗、双通带的带通滤波器的新方法,主要利用双频谐振器能够同时工作于两个频段的特点,通过合理设计使谐振器间的耦合结构和馈电点位置在两个频段上具有相同的结构参数,从而实现小型化双频滤波器.为验证该方法的可行性,设计了一种基于阶跃阻抗谐振器(SIR)结构的双频滤波器.该滤波器工作频率为2.4 GHz和5.2 GHz,回波损耗都低于-20 dB,插入损耗小于1 dB,相对带宽FBW均为20%,尺寸为6 mm×15 mm(0.08λg1×0.19λg1).对该滤波器进行了仿真、加工和测试,发现测量和仿真的结果具有很好的一致性.     

Active quasi-circulator realisation with gain elements and slow-wave couplers

A microstrip active quasi-circulator is presented using two generic amplifier blocks and two power couplers. The power couplers are parallel-coupled lines with a slow-wave structure in order to improve the isolation between ports of the quasi-circulator. A detailed analytic design procedure is presented for the slow-wave couplers based on the capacitive coupling modelling approach for coupled transmission lines. Experimental results show that the quasi-circulator has an insertion loss between 1 and -2 dB, a return loss better than 11 dB at each of the ports and an isolation better than 20 dB from 1.0 to 3.0 GHz. The input 1 dB compression point is 14 dB m at 2.4 GHz.     

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+.     

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.     

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.     

Improved equivalent circuits for complementary split-ring resonator-based high-pass filter with C-shaped couplings

The authors modify the complementary split-ring resonator (CSRR) with dual C-shaped couplings for high-pass filter (HPF) design and propose improved equivalent circuits as a means to analyse the filter. The p-type circuit of the dual C-shaped coupling in the CSRR-based HPF is presented to have the improved equivalent circuit in contrast to the conventional equivalent circuit. At 3 dB, the cut-off frequency f _{? 1.74 GHz, the maximum IL is within 0.33 dB up to 8 GHz and the 65.81 dB rejection extends down to 0.53 GHz. Simulation and measurement results including surface current distributions and frequency responses are presented and discussed.}     

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.     

Analytical closed-form solutions for different configurations of parallel-coupled microstrip lines

Closed-form solutions are presented for the even- and odd-mode impedances of the parallel-coupled microstrip lines with different configurations. The first set of equations is for the conventional-coupled microstrip lines. The second set is for the parallel-coupled microstrip lines with a slotted ground plane and the third set is for the parallel-coupled microstrip lines with a slotted ground plane and a floating-potential conductor added to cover most of the slot in the ground plane. The solution is achieved using the conformal mapping technique, which also considers the effect of any fringe capacitor that has an impact on the impedance of the coupled lines. To validate the accuracy of the presented equations, a comparison is made with the available empirical solution (only for the conventional-coupled microstrip lines), a numerical solution (using Galerkin?s technique) and the full-wave electromagnetic solution using the software HFSS. The result of the comparison indicates the high accuracy of the presented equations over a wide range of design parameters. The difference between the calculated values using the derived equations and those from the full-wave electromagnetic analysis is ,5% for most of the cases. To validate the derived equations experimentally, they are used to design a 3 dB coupler. The result of measurements on the manufactured coupler confirms the accuracy of the presented equations.     

Negative permittivity meta-material microstrip binomial low-pass filter with sharper cut-off and reduced size

A binomial low-pass filter provides the flattest pass-band response but slow attenuation transition. A design for improving the roll-off performance based on the negative-epsiv property of complementary split-ring resonators is presented, whilst maintaining the filter pass-band performance. By properly designing and integrating the complementary split-ring resonators with the low-pass filter, not only can the roll-off of the filter be significantly improved, but also the filter size further reduced. The measured results indicate that the proposed structure achieves a flat pass-band with no ripples as well as has a selectivity of 32 dB/GHz. This significantly exceeds the 17 dB/GHz selectivity of the conventional design. Furthermore, the proposed filter has a size smaller by 16%.     

低信噪比下基于Chirp信号的频率特性测试方法

提出采用带通滤波和小波包变换对响应信号进行预处理,再由FFT分析和处理获得系统频率特性曲线的方法,较好地解决了低信噪比下的系统频率特性测试问题,并降低了测试时对采集系统的硬件要求。实验结果表明：对于截止频率以下的频段,在信噪比较低甚至为-20 dB时,可以得到精度不低于1 dB的幅频特性曲线和不低于3°的相频特性曲线,完全满足系统性能评价和控制器设计的应用要求。     

Design and application of microstrip parallelcoupled lines employing step-impedance transmission-line compensation

The application of step-impedance transmission lines (SITLs) to improving the directivity of parallelcoupled microstrip lines is presented. A simple design procedure for two configurations based on the SITL technique is given. The application of the technique is demonstrated practically with a design at 0.9 GHz on an RF60 substrate. The directivities obtained from the measured results are improved by more than 6 and 30 dB compared with the designed uncompensated coupler. The compensation technique is then applied to the design of a coupled-line resonator and bandpass filter for suppressing harmonic responses in these circuits. Experimental results show that the second harmonic in the filter response is suppressed by 30 dB.