几种自适应IIR陷波器的复数算法及其应用

在自适应IIR陷波器实数算法的基础上,本文提出了三种基于梯度的自适应IIR陷波器的复数算法,并进行了仿真比较。结果表明,这三种复数算法均可检测复信号,并估计信号频率,其中"改进的"简化格型IIR陷波器复数算法收敛速度快、低信噪比下稳定性能好。湖上试验表明该算法不仅实时性好,而且在低信噪比下的检测效果令人满意。     

激光多普勒测量自适应陷波器去噪研究

针对激光多普勒测量中声光调制、电光调制等引入的多频率噪音干扰,提出一种兼顾收敛性、鲁棒稳定性的自适应陷波器去噪方法.并在时域内研究自适应陷波器算法及其构造,最后给出了仿真实例.该算法不需具体的激光多普勒测试系统模型,方法简单,易于实现,试验结果表明了该方法的有效性.     

自适应陷波滤波器应用研究

本文介绍自适应陷波滤波器的基本理论,提出了设计极窄带自适应陷波器和滤波器的方法,介绍了用作相位估计器的概念。作者证明自适应相位估计器是理想条件下的最大似然比相位估计器,计算机仿真研究和硬件实验结果均表明该估计器有良好的性能,它的显著优点是同时完成了信号的检测和相位差的估计。     

矩孔光子晶体可见光谱段窄带偏振陷波研究

提出一种可见光谱段内窄带偏振陷波滤波的矩孔光子晶体结构。通过建立矩孔光子晶体模型,将矩孔光子晶体结构等效为介质层-光栅层-介质层周期结构,利用Rugate滤波理论对矩孔光子晶体结构进行分析,结合等效介质理论(EMT)和传输矩阵方法(TMM)对结构模型的入射光s偏振、p偏振的透过率进行仿真。另外讨论了矩孔光子晶体纵向周期数m、光栅层填充比f、厚度d等参数对偏振陷波的中心波长、带宽以及截止带透过率的影响。针对417,497,582,685nm中心波长,设计带宽为10nm的p偏振窄带陷波结构,并用时域有限差分方法(FDTD)进行仿真验证,结果表明,矩孔阵列结构可以实现可见光谱段内窄带偏振陷波滤波。     

平行声屏障的陷波模态及其插入损失优化

为了改善平行声屏障的性能，本文基于有限元仿真的方法对其陷波模态和插入损失进行了研究。其中，陷波模态是平行声屏障的固有性质，与其几何参数有关。当陷波模态处于共振频率时，平行声屏障内部声场的声能量达到峰值，同时声波垂直入射到声屏障的顶端，使声影区的衍射声能也达到峰值，最终导致插入损失显著下降。本文还对3种优化平行声屏障插入损失的方法进行了分析。结果表明，楔形和扩散型声屏障可降低声波的多次反射效应对插入损失的影响，但是对陷波模态的改善较小。而吸声型声屏障有效的抑制了陷波模态对插入损失的不利影响，从而改善了平行声屏障的性能。     

双枝节加载的L波段宽带高隔离度定向耦合器

提出了一种小型化双枝节加载的L波段微带线定向耦合器。使用功率相消技术提高定向耦合器的隔离度,并且采用两根长度不同的加载枝节分别在两个相近的频点上反射信号,从而实现耦合器的带宽扩展;同时采用缺陷地结构的慢波特性减小该定向耦合器的物理尺寸,并利用缺陷地结构产生的陷波,合并上述两根枝节反射抵消产生的的两个陷波,进一步提高定向耦合器的带宽和隔离度。该耦合器工作在L波段,耦合度约为10 dB,在整个L波段内的隔离度均优于?20 dB,最大约为?52.81 dB,相对带宽为60%。最后对设计的定向耦合器进行加工和测试,测试与仿真结果一致性较好,证明了该电路的可行性。     

一种带有陷波单元的高温超导滤波器设计

提出了一种带有陷波单元的新型高温超导滤波器设计结构,在输入、输出馈线附近设置陷波单元对特定频率产生陷波作用,在滤波器的传输特性上成传输零点,提高了滤波器设计的灵活性,基于这种新型结构设计了高边缘陡峭度滤波器和邻频双通带滤波器.     

光纤射频滤波网络与最佳陷波条件的研究

研究了利用光纤网络实现的射频滤波技术，讨论了几种基本单元结构的冲击响应函数与最佳滤波条件。给出了各单元实现理想陷波的参量取值范围，发展并验证了为获得最佳陷波的耦合器系数—损耗补偿方法。实验表明这一方法是简便有效的，并与理论分析符合得很好。     

声表面波陷波器与梯形结构相结合的滤波器

用单端对SAW谐振器取代LC低通滤波器中的电容可构成宽通带陷波器。它具有频率选择性好，通带插损低，对陷波频点抑制较高的优点。将这种陷波器与梯形滤波器结合，能实现一种在通带具有低插损，而在特定频段达到高抑制的滤波器，从而可用于双工器中。本文首先分析了这种组合结构的构成原理及实现方法；然后进行理论模拟，并进行了实验验证。     

VHF波段变容管调谐式超导陷波器

设计制作了一款VHF波段变容管调谐式超导陷波器,该陷波器采用一种结构紧凑的电容加载的矩形回路谐振器,谐振器与主线之间的耦合形式为混合耦合。通过调节加载在谐振器上变容二极管的反偏电压,实现带阻滤波器中心频率可调。测试表明,陷波器中心频率可调范围为251~360MHz,陷波器中心频点抑制40dB,3dB带宽9dB,插入损耗0.5dB。     

包含源与负载耦合的滤波器诊断与调试方法

柯西法目前仅适用于诊断不包含源与负载耦合的带通滤波器。为解决这一问题,提出了一种能够诊断包含源与负载耦合的带通、带阻谐振腔滤波器的方法。利用遗传算法优化获得源与负载耦合系数并移除滤波器输入/输出端口处传输线引起的S参数的相位加载效应;使用柯西法一步确定仿真S参数对应的特征多项式;从获得的源与负载耦合系数和特征多项式中,利用已有的技术诊断出N+2阶耦合矩阵。此方法可用于指导滤波器的调试,通过对比理想的耦合矩阵与提取的耦合矩阵之间的差异,可确定滤波器问题出自何处以及调试的方向,从而加快滤波器的设计与实现。     

Tunable bandstop filter for binary objects: A self-imaging technique

Negative Talbot images are employed to obtain a simple tunable, bandstop filter for bunary objects, that are composed of pieces with Ronchi rulings (Rademacher functions).     

基于两滤波器级联和饱和吸收体的单纵模双波长光纤激光器

提出和证实了一种光纤环形激光器. 将一个带通滤波器与一个带阻滤波器级联,用一段保偏掺铒光纤作为饱和吸收体,得到了一种单纵模双波长光纤激光器. 结果表明,该激光器波长间隔为0.4 nm,边模抑制比大于49 dB.如果将两个波长进行差拍,该激光器有潜力得到49.85 GHz的微波信号.     

一种结构新颖、边带陡峭的高温超导带阻滤波器

研制了一种结构新颖的高温超导带阻滤波器.这种带阻滤波器的设计值为:中心频率,2.5GHz带内最大衰减65dB.而用YBCO薄膜制成的带阻滤波器实物经调谐,其中心频率与设计值相同,带内最大衰减为73dB,优于设计指标.该滤波器的主要优点是体积小、边带陡,而且可以与其他滤波器组合使用.     

Analysis of the characteristics of NRD waveguides loaded with periodic metallic strips by using the method of lines for millimeter wave filter and antenna application

In this paper, the propagation characteristics of NRD waveguide loaded with periodic metallic strips are analyzed in terms of the method of lines. Numerical results show that such structures are most suitable for millimeter wave bandstop filter and NRD waveguide beam scanning leaky wave antenna application.     

Transmission characteristics of photonic crystal waveguides with stubs and their application to optical filters

We study the transmission characteristics of a photonic crystal waveguide with a single stub of a finite length and propose a double-stub waveguide structure for its application to optical filters. The proposed device operates as a Fabry-Perot interferometer and can be used as a broad bandstop filter and a narrow bandpass filter. These filters are inherently compact and their center frequency is given by the resonant frequency of the stub.     

Multiple interaction bandstop filters based on the Talbot effect

We report on two tunable, bandstop spatial filters, which are based on the Talbot effect. The light interacts with more than two gratings, arranged in series. The techniques may be considered as the analogues of the Fabry-Perot interferometer and the Lyot-Öhman filter, respectively. Some experimental results are included.     

Modeling and preparation of practical optical filters

Multilayer bandpass and bandstop filters have been produced using electron beam evaporation. Initially bandstop filter is modeled with non absorbing zinc sulphide (ZnS) and zinc selenide (ZnSe). When the absorption data was incorporated for the said materials significant absorption was observed at shorter wavelengths of the spectral band restricting the practical usage of the filter. ZnS and ZnSe were then replaced by dispersive silicon dioxide (SiO₂), tantalum penta oxide (Ta₂O₅) and titanium dioxide (TiO₂) along with their absorption and the filters are optimized to get desired bandpass and bandstop data. Bandpass and bandstop filters with desired performance were experimentally characterized with two combinations SiO₂/Ta₂O₅/glass and SiO₂/TiO₂/glass. The measured average transmission for both combination (bandpass) in the pass band was about 92% with T < 1% in the stop band. Slightly narrow bandwidth was observed for SiO₂/TiO₂/glass as compared to SiO₂/Ta₂O₅/glass which is attributed to layers densification. Similarly T_avg ⩾ 80% was achieved for two combinations of bandstop filters with T < 0.1% in the stop band. The structure and surface morphology of the prepared filters were characterized by X-ray diffraction and scanning electron microscopy. XRD analysis reveals amorphous structure. SEM analysis also reveals that the layers are compact and have good surface quality.     

Dual-Wavelength Erbium-Doped Fibre Ring Laser by Cascading Tunable Bandpass Filter with Bandstop Filter

A novel fibre ring laser is proposed and successfully demonstrated. By cascading a tunable bandpass filter with a bandstop filter to construct the desired narrow dual-transmission-peak spectrum, and employing a segment of unpumped erbium-doped fibre as a saturable absorber, a stable fibre ring laser is achieved at room temperature. The proposed laser can operate in dual-wavelength with the wavelength spacing of 0.48 nm and the extinction ratio more than 50 dB or switch between the two wavelengths by adjusting a polarization controller. The stability is investigated experimentally and explained theoretically.     

Optimization of long-period grating inscribed in large mode area photonic crystal fiber for design of bandstop filter

By inscribing long period grating (LPG) in a photonic crystal fiber (PCF), optical filters for communication wavelengths can be fabricated. In this paper, by utilizing coupled-mode theory and enhanced improved vectorial effective index method, a design of bandstop filter based on optimal LPG parameters is presented where the optimized full-width half-maximum (FWHM), the number (N) and total length of gratings of LPGs (L) are determined. As a result, by the determination of optimized LPG parameters with an optimum length of L_opt=6.5 mm and optimum number of grating N_opt=27 inscribed in the PCF, a bandstop optical filter with FWHM=1 nm is designed.