Design of Triple-Passband Microwave Filters Using Frequency Transformations

This paper introduces a synthesis method for triple-passband microwave filters. A frequency transformation is developed for finding the locations of poles and zeros of the triple-passband filter. The poles and zeros obtained as such are optimized to achieve a transfer function with a reduced number of transmission zeros in order to reduce the number of cross-couplings. Six- and 12-pole triple-passband filters are synthesized for validation of this proposed method. A 12-pole triple-passband filter is fabricated with a microstripline structure and shown to provide good agreement between synthesis and measurement results. Finally, the frequency transformation for asymmetric triple-passband filters is briefly discussed.     

Generalised lattice transformation for crystal filters

Crystal lattice filters are usually based on the transformation of a lowpass Brune section to a second-order lattice section. This letter describes a generalisation, which transforms n Brune sections simultaneously into a lattice of order 2n, and which offers advantages for high-order filters, or filters with complex transmission zeros.     

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.     

Synthesis and design of in-line N-order filters with N real transmission zeros by means of extracted poles implemented in low-cost rectangular H-plane waveguide

In this paper, an extension to the extracted pole technique for synthesizing N-order filters with N-transmission zeros at real frequencies is presented. In addition, a new bandpass rectangular waveguide H-plane low-cost configuration filter for high-power low-loss application (patent pending) that implements a filtering function with finite real frequency transmission zeros is proposed. This structure operates as a resonant cavity in transmission at central frequency of the bandpass and simultaneously introduces a controlled transmission zero out of the bandpass. Since every double-controlled electrical behavior cavity introduces a transmission zero, it is possible to introduce as many transmission zeros as the order of the filtering function. In order to validate the synthesis procedure and the new structure, different filters have been designed: a second-order filter with two transmission zeros, a third-order filter with one transmission zero, a fourth-order filter with two transmission zeros, and finally, an eighth-order filter with two transmission zeros. The last two have been manufactured, showing an excellent agreement between the measurement and theoretical simulation.     

Filters with Single Transmission Zeros at Real or Imaginary Frequencies

A new unified theory is presented for the synthesis of exactly equiripple low-pass prototypes having: a) one simple pole of attenuation at a real frequency; or b) a single pair of real-axis transmission zeros (giving linear-phase performance). These types of filters may be regarded as representing the least possible degree of complication over the conventional Chebyshev filter, and are usually realized with one extra cross coupling in the structure. It is demonstrated that this gives much improved skirt selectivity in the case of a finite frequency pole, making it a viable intermediate case between the Chebyshev and elliptic function filters, while in the case of real-frequency zeros, very flat group delay over 50 percent of the passband is achieved with minimal cost in insertion loss and skirt rejection. Approximate and exact synthesis techniques are described, including results for the previously neglected odd-degree case. Experimental results demonstrate agreement with theory.     

Design techniques for dual-passband filters

This paper introduces two possible approaches to the design of microwave filters presenting two passbands separated by one rejection band, which is created by suitably placing transmission zeros in the stopband. In the first method, the two passbands have almost equal extension and the transmission zeros are symmetrically placed in the stopband; the second method instead allows the synthesis of filters with different passbands width and all the transmission zeros in the stopband placed at the same frequency. Both design methods are based on suitably defined frequency transformations and employ well-established prototype synthesis techniques; the practical implementation is performed through the classical multiple-coupled cavity topology. Two test filters operating in the global system for mobile communication 800-MHz band, designed with the described procedures and actually fabricated, have validated the novel design methods.     

Design Of Maximally Selective Generalized Chebyshev Filters

In this paper, a complete procedure is presented for the synthesis of a class of generalized Chebyshev filters with a maximum of four real transmission zeros of any multiplicity, having an equiripple characteristic in the passband and the stopband, and maximum selectivity. The frequencies of magnitude characteristic extreme values in the stopband are calculated in the closed form. The transmission zeros are obtained by solving a set of nonlinear equations. New formulas for orders of zeros of maximally selective filters are deduced, and these are very useful in the design procedure.     

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.     

Synthesis of N-order filters with N transmission zeros at real frequencies by means of extracted poles

The synthesis of N-order filters with N transmission zeros at real frequencies by means of extracted poles is presented. A procedure to extract the circuit elements that implement the finite insertion losses for infinite frequency is explained. To verify this procedure, three different implementations of a fourth-order filter with four transmission zeros are presented.     

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.     

Design of generalized Chebyshev filters with asymmetrically located transmission zeros

A simple design technique is introduced for generalized Chebyshev filters with asymmetrically located transmission zeros. The efficient and exact procedure is given for the calculation of transmission zeros for a class of generalized Chebyshev low-pass prototype filters with a maximum of four asymmetrically located transmission zeros of any multiplicity. This technique is based on obtaining the frequencies of magnitude characteristic extreme values in closed form, and after this, transmission zeros can be calculated by solving a system of nonlinear equations. Novel formulas for orders of zeros of maximally selective filters with equiripple characteristics in the passband and stopband are deduced. The obtained results are verified and illustrated by given examples.     

Transmission-line filters with capacitively loaded coupled lines

Coupled lines with loads at one end, which can create tunable transmission zeros, are studied in this paper. The equation for the transmission zeros is derived from the analysis of even- and odd-mode excitations. Based on this equation, coupled lines with different loads are analyzed and the rules for controlling the transmission-zero frequency are given. The structures are used in the designs of several second-order filters and they are experimentally verified. The use of a skew-symmetric (0/spl deg/) feed structure in these filters is also discussed and an example is given.     

广义Chebyshev最优滤波器设计

本文论证了等波纹广义Chebyshev函数滤波器的最优化特性,提出了由设计指标得到广义Chebyshev函数的方法,并且引入信号流图非常简便的得到了对应网络的拓扑结构,最终完成滤波器的设计.本文对具有带外传输零点的滤波器设计具有相当重要的意义.     

Synthesis of arbitrary digital transfer functions using allpass-based structures derived via LBR two-pair extraction procedure

The implementation of a digital filter transfer function with all transmission zeros on the unit circle is developed via the synthesis of an appropriate allpass function. The synthesis procedure is based on the LBR-extraction approach. The resulting structure is in the form of a doubly terminated cascade of lossless (LBR) two-pairs, with each two-pair realizing a single real or a pair of complex transmission zeros. The Concepts of complete and partial 1 removals, and 1 shifting are introduced and utilized during the synthesis process. The resulting structures have several properties in common with the Gray and Markel lattice filters, but do not require tap coefficients for numerator realization. The building blocks used in this paper are similar to those in certain wave-digital filters and orthogonal filters.Work supported in part by NSF Grant Number ECS 82-18310 and in part by NSF Grant Number ECS-8508017.     

Partial $H$-Plane Filters With Multiple Transmission Zeros

This paper presents partial $H$-plane filters with multiple transmission zeros using a narrow $H$ -plane slot of open-ended evanescent waveguide. Each narrow $H$-plane slot operates as an admittance inverter and, simultaneously, provides the attenuation pole due to its resonance behavior at a particular frequency. Thus, the number of transmission zeros is equal to that of the $H$-plane slots. The filters with multiple transmission zeros are simply implemented without any additional coupling and extra modification of the filter structure. Two filters are designed by half- and quarter-wavelength resonators, respectively. The measured results are in good agreement with simulated results.      

双模方形带通滤波器的分析、建模及设计

本文报道一种利用谐振器中缺口位置设计双模带通滤波器的新方法.用这种方法既可以实现具有一对传输零点的双模带通滤波器,也可以实现无传输零点的双模带通滤波器.通过分析缺口位置对谐振器内电场模式分布的影响,建立了双模滤波器的拓扑结构图.利用全波仿真软件,基于不同的缺口位置设计了中心频率为2.05GHz,带宽为100MHz的两种...     

Maximally selective generalized Chebyshev filters with asymmetrically located transmission zeros

An efficient design procedure for generalized Chebyshev filters with asymmetrically located transmission zeros is presented in this paper. The exact and simple procedure is given for the calculation of transmission zeros, for a class of generalized Chebyshev low-pass prototype filters with a maximum of three asymmetrically located transmission zeros of any multiplicity. This procedure is based on finding the frequencies of magnitude characteristic extreme values in closed form. New formulas for orders of zeros of maximally selective filters with equi-ripple characteristics in the pass-band and stop-band are deduced, and these are very useful in the design procedure. The obtained results are verified and illustrated by corresponding examples.     

脊双模波导滤波器的分析及设计

介绍了一种能实现脊双模波导滤波器的新型结构,分析了其腔内模式的耦合极性,利用不同的耦合极性对频率响应的影响可实现具有一对传输零点的双模滤波器,也可实现无传输零点的双模滤波器.以相同脊谐振单元不同的放置方向组成的两种带通滤波器为例,利用AnsoftHFSS仿真得到了两种不同的频率响应,结果与理论分析一致.最后设计出了一个六阶三传输零点的双通带滤波器,带内插损均小于0.6 dB,回波损耗小于-15 dB.     

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)     

广义Chebyshev滤波器传输零点的确定

传输零点的确定是交叉耦合滤波器综合的最基本要素.本文利用广义Chebyshev函数的极值特性以及滤波器阶数与传输零点最大值的关系,提出了一种根据滤波器特性指标同时确定广义Chebyshev滤波器的阶数和传输零点位置的方法,弥补了传统方法中传输零点确定的人为随意性,在满足技术指标条件下,实现了广义Chebyshev滤波器阶数最少,传输零点位置最佳.几个数值实验显示了该方法的过程和有效性.