Direct synthesis of a new class of bandstop filters

A direct synthesis technique of a new class of bandstop coupled resonator elliptic filters is presented. Two different coupling schemes, which both include source-load coupling are used. The first coupling and routing scheme is the standard folded structure used in implementing bandpass elliptic filters with N transmission zeros using N resonators. The second coupling scheme is identical to the multipath parallel structure, which was recently introduced for the synthesis of fully elliptic bandpass filters. In both cases, the source and load are directly coupled by an inverter in order to generate the required transmission zeros. It is shown that, for each coupling scheme, two distinct solutions that are not related by a similarity transformation exist. Furthermore, the two solutions both have realistic coupling coefficients in contrast to the bandpass case where only one solution, in general, is practical. It is also shown that the same coupling scheme can implement pseudoelliptic bandstop filters with N/sub z/ reflection zeros where 0/spl les/N/sub z//spl les/N.     

A Compact Open-Loop Filter With Mixed Electric and Magnetic Coupling

A novel cascaded microstrip open-loop resonator filter with controllable electric and magnetic mixed coupling is presented to have one or more transmission zeros. For two coupled resonators, the coupled sides with the maximum magnetic field are combined with their open gaps with the maximum electric field, creating the electric and magnetic mixed coupling. By adjusting the distances between resonators and the positions of open gaps in a mixed coupled filter, the coupling coefficients can be changed, and controllable transmission zeros can be produced in the lower stopband, upper stopband, or both. Design and fabrication of the proposed second-and fourth-order filters show the advantages: such as a smaller number of resonators, higher rejection level, as well as asymmetrical response; moreover, the location of the transmission zeros can be precisely controlled.     

Pseudo-elliptic slow wave line

Quasi elliptic filters are of great demand in the present day communication systems. Coupling matrix analysis of pseudo-elliptic low pass filter using conventional microstrip line is presented in this paper. The conventional microstrip line has no non-zero cut off frequency. The conventional microstrip line is transformed into a pseudo-elliptic low-pass filter using the concept of slow wave. The slow wave microstrip line exhibits pseudo-elliptic low-pass behavior with transmission zeros at finite frequencies unlike the conventional Butterworth and Chebyshev filters. The coupling matrix of the slow wave microstrip line is arrived at by using the generalized Chebyshev functions. The coupling matrix of the slow wave line is validated using the MATLAB tool box. Finally, the prototype is fabricated and the performance is measured.     

An original approach to the design of bandpass cavity filters withmultiple couplings

A novel approach to the design of general cavity filters with each cavity coupled to an arbitrary number of other cavities is presented. This approach is based on a suitable characterization of the filter structure which does not require one to model separately the cavities (resonators) and the coupling elements. Suitably defined equivalent admittances are associated with each cavity allowing one to design the filter structure once the parameters of a suitable low-pass prototype are given; an efficient procedure for the synthesis of such a prototype with equiripple passband response is also presented which allows one to arbitrarily prescribe transmission zeros placed in the complex plane (even asymmetrically). The described design approach is particularly convenient when the filter structure does not allow a simple modeling of the resonators and coupling elements separately. This is the case of slot-coupled cavity filters and of filter structures based on arrays of coupled transmission lines. It is also shown that the simplified design approach often adopted in the past, where only two coupled cavities at a time are considered, can produce large errors even in the case of filters with all attenuation poles at infinity (i.e., two couplings per cavity)     

信号流程图理论分析多环谐振滤波器特性

微环谐振腔以其功能多样、结构简洁、集成度高等特点已经成为当前的研究热点。采用多环结构形成的滤波器能够实现在通带内比单环谐振滤波器更为陡峭的滚降、更平坦的峰顶和更好的抑制阻带。利用信号流程图法(SFG)推导了串联耦合和并联耦合两种形式的多环谐振滤波器的系统传递函数公式。在串联结构中,滤波器的输出特性主要受到耦合系数和损耗的影响;在并联结构中,通过优化环间距,从而使下载端输出光谱达到比较好的形状。     

Narrow-Band Stripline or Microstrip Filters with Transmission Zeros at Real and Imaginary Frequencies

Simple approximate design equations are derived in this paper for an even degree (n /spl ges/ 6) low-pass inverter capacitance prototype filter having single transmission zeros at both real and imaginary frecuencies. This is achieved by utilizing one or two additional couplings. The transmission zeros improve considerably the passband group delay and increase the skirt selectivity compared to those of the ordinary Chebyshev prototype. An exact and more complicated method based on the known generalized Chebyshev rational function approximation is also presented for the comparison. The prototype with one additional coupling is utilized to realize narrow-bandpass printed circuit filters consisting of half-wave resonators.     

Analysis of electric coupling between slotted cylindrical ringresonators

Electric coupling necessary for realising filters with transmission zeros is investigated for slotted cylindrical ring (SCR) resonators. The transmission line matrix (TLM) method is applied to the analysis of couplings between these resonators. Typical coupling curves of practical importance are presented, which help in the design of SCR resonator filters     

Compact Planar Quasi-Elliptic Function Filter With Inline Stepped-Impedance Resonators

Compact microstrip bandpass filters of orders N = 4,6, and 8 with quasi-elliptic function responses are synthesized with inline stepped-impedance resonators. The filters have enhanced transition responses since two transmission zeros are generated on both sides of the passband. Existence of these two zeros is investigated by formulating the Y-matrix of the equivalent circuit for the filter and taking adjacent and nonadjacent coupling into account. Some matrix elements Y_j,j+2 representing coupling between two nonadjacent resonators are shown to have the opposite signs in both the lower and upper sides of the center frequency. This property leads to creation of the two transmission zeros on both sides of the passband. It is demonstrated that one more zero can be created in the rejection band by the tapped-line input/output scheme. Experimental circuits on substrates with epsiv_r = 2.2 and 10.2 are measured to validate the theory and design.     

General Extracted Pole Synthesis Technique with Applications to Low-Loss TE/sub011/ Mode Filters

A novel synthesis technique is developed for two-port networks which possess finite real frequency transmission zeros. The low-pass prototype is synthesized in the form of a network with complex conjugate symmetry where the real frequency transmission zeros are extracted from both ends and realized by simple resonators separated by phase shifters. The remaining transmission zeros are realized by the central part of the filter in the form of a cross-coupled double array. This prototype is particularly suitable for designing waveguides bandpass filters and each real frequency transmission zero is independently tunable. Furthermore, in the case of the most complex transfer function with all possible types of transmission zeros, the realization requires only one type of coupling which is necessary in the important case of TE/sub011/ cylindrical mode cavity resonators. The general synthesis technique is given and the process illustrated by a nontrival example. Additionally, from the results of a computer program based upon the synthesis techniques, the important differences between the possible prototype forms for the same transfer function resulting from extracting the transmission zeros in different orders are cited.     

串联微环谐振器的光学特性

根据波导耦合方程,导出了串联微环谐振器的传输矩阵,并分析了环数、环间耦合系数以及损耗对串联微环谐振器输出特性的影响。数值模拟表明,串联微环谐振器具有光子带隙的特征。当环数增加时,通带内满足谐振条件的波长数增加;当环间耦合系数增加时,可使通带带宽加宽;通过适当选择环数和环间耦合系数,可以实现滤波和波分复用(WDM)的功能。选用脉冲宽度为50 ps的高斯型激光脉冲注入微环谐振器,发现当环间耦合系数较小时,出射脉冲相对于入射脉冲具有光学延迟的效果,并且随着环数的增加,延迟时间逐渐增大,而当环间耦合系数较大时,光学延迟效果不明显。     

基于LTCC技术的椭圆函数低通滤波器设计

随着无线通信领域的快速发展,人们对微波滤波器性能的要求也越来越高。文章根据滤波器的分类和特点,研究了集总元件滤波器引入传输零点的规律和方法,分析并对比了三种不同类型低通滤波器的衰减特性。根据设计指标要求,基于LTCC技术设计了一款高性能小型化的椭圆函数七阶低通滤波器。滤波器的等效电路包括串联支路中的4个电感和并联支路中的3个LC谐振腔,共10个元件。通过对滤波器模型物理结构的优化,减小了滤波器内部元件间的寄生耦合效应,并在阻带中成功引入了传输零点,改善了滤波器的性能。     

Compact microstrip resonators for 900 MHz frequency band

A technique to reduce the size of planar resonators is investigated using a transmission line model and a finite-difference time-domain (FDTD) method. New miniaturized square microstrip resonators are proposed for 900 MHz band. The resonators offer low impedance sections leading to a better handling of power. The feasibility of compact filters using the proposed resonators is demonstrated. The input/output coupling lines of a two-pole filter have been positioned in a way that produces a filter response with transmission zeros on the both sides of the pass-band. Sharper skirts and higher out-of-band rejection are obtained for four-pole filters with cross-coupled resonators.     

Synthesis of an in-line prototype filter with two transmission zeros without cross couplings

This letter describes a method for synthesizing a general in-line prototype filter presenting one or two transmission zeros without using cross couplings; the basic topology is constituted by resonators coupled through inverters, with input and/or output taken at the second and/or last but one resonators. In this case, the first and last resonators, tuned at frequencies in the stopband, produce two zeros in the transfer function. It is shown that, even if it is not possible to exactly synthesize this structure with extracted poles techniques, an approximated design procedure can be derived; the procedure is based on the synthesis of a low pass prototype with multiple couplings starting from source and/or load, followed by suitable network transformations. This design technique can be easily implemented in case of classical combline or interdigital filters.     

General Coupling Matrix Synthesis Method for Microwave Resonator Filters of Arbitrary Topology

This letter presents a new approach to synthesize the resonator filters of an arbitrary topology. This method employs an optimization method based on the relation between the polynomial coefficients of the transfer function and those of the S₂₁ from the coupling matrix. Therefore, this new method can also be applied to self‐equalized filters that were not considered in the conventional optimization methods. Two microwave filters, a symmetric 4‐pole filter with four transmission zeros (TZs) and an asymmetric 8‐pole filter with seven TZs, are synthesized using the present method for validation. Excellent agreement between the response of the transfer function and that of the synthesized S₂₁ from the coupling matrix is shown.     

Synthèse et réalisation de filtres hyperfréquences à cavités bimodes ayant une réponse en fréquence dissymétrique

This article presents the study and the realization of microwave filters with asymmetric frequency characteristics using dual-mode cylindrical cavities. The synthesis method of such characteristics using generalized Chebyshev transfer functions is described. These functions allow the realization of symmetrically or asymmetrically prescribed transmission zeros. The method consists in synthetizing a generalized low-pass filter, in order to calculate the coupling matrix, the dual-mode structure has to realize. Concerning the practical design of the filter, a method is described for the realization of asymmetric characteristics with dual-mode cavities. Several measured characteristics of different laboratory models are presented.     

Pseudo-elliptic microstrip line filters with zero-shifting properties

The paper presents a new design of pseudo-elliptic microstrip line filters. These filters employ a coupling scheme which allows shifting of transmission zeros from one side of the passband to the other by only changing the resonant frequencies of the resonators. To demonstrate the performance of these filters, a fourth-order bandpass filter with one transmission zero in the upper stopband is first designed. A second filter with a transmission zero in the lower stopband is then designed by simply adjusting the lengths of the resonators followed by minor optimization to account for the fact that the resonant frequencies can not be changed without slightly affecting the coupling coefficients in the used layout. Measured and simulated results are presented.     

A New Coupling Matrix Extracting Method From the Frequency Response

Coupled resonators are widely used in many applications, especially for filters. It is necessary to know the coupling matrix of those resonators in order to further modify and/or optimize the existing design. In recent years, many efforts have been made to generate a coupling matrix. In this paper, a new method is proposed, which can be applied for both the synchronous and asynchronous coupled resonators. With this method, the eigenvalues and eigenvectors of the coupling matrix can be generated directly from the simulated frequency responses, and the coupling matrix can then be determined. Typical examples are illustrated for the cases such as a quadruplet with an image, real, or complex transmission zeros. The impact of loss is also discussed. As a matter of fact, this method has been successfully used in the design of high-temperature superconducting filters     

一种新型广义交叉耦合滤波器的设计

含广义交叉耦合的N个谐振器滤波器,即含源-负载交叉耦合的滤波器能产生N个传输零点,通过给出这种滤波器的等效网络模型和传输函数,设计了两种新颖六边形结构的含源-负载交叉耦合的微带滤波器,一种为对称结构,一种为非对称结构.对其进行了仿真分析,仿真结果与理论值吻合较好.与传统两腔发夹形滤波器相比,这种两腔六边形结构的滤波器尺寸要缩小27.5%,频率选择性更高.     

Novel realization of monotonic Butterworth-type lowpass, highpass,and bandpass optical filters using phase-modulated fiber-opticinterferometers and ring resonators

A novel realization of monotonic Butterworth-type lowpass, highpass, and bandpass optical filters (from their electrical digital filter characteristics) by cascading the all-pole and all-zero resonators is presented. A graphical method for fast derivation of the transfer functions, quick inspection of the resonance effects, and important characteristics of any photonic circuits is described. It is shown that incorporation of the optical amplifiers and optical phase modulators into the delay lines of two basic optical resonators, whose pole and zero can be adjusted independently of each other, provides great design flexibility which would otherwise not possible using conventional passive optical resonators. Possible applications of these optical filters as optical pulse equalizers and receiver shaping filters in long-haul coherent lightwave transmission systems are discussed. Possible application of basic resonators comprising of optical phase modulators as tunable optical filters for spectrum analyzers is also considered     

Design Methods for Micro-Electro-Mechanical Bandpass Filters with Transmission Zeros

A design method for high-order electro-mechanical filters allowing the synthesis of architectures of electro-mechanical filters from equivalent electrical prototypes is presented. Conditions for existence of the equivalent mechanical system for a given electrical network are derived. This method is applied to the problem of the design of band-pass electro-mechanical filters with transmission zeros in the stopband. Electro-statical coupling of micro-mechanical resonators that avoids the use of a mechanical coupling spring is introduced. The application to the simulation and design of a bandpass filter with finite transmission zeros implemented in a thick-layer epi-poly silicon micro-machining technology is shown.