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.     

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.     

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.     

Synthesis and design of novel in-line filters with one or two real transmission zeros

A direct synthesis and design technique of pseudoelliptic in-line filters with one or two real transmission zeros (TZs) is presented. It is shown that the phase of the reflection coefficient must be properly and uniquely determined for the synthesis to succeed. The TZs (attenuation poles) are brought about and independently controlled by dedicated resonators at the input and output. Each attenuation pole is located at the resonant frequency of its dedicated resonator. Frequency-independent reactances at the input and output are used to replace the phase shifts used in the extracted-pole technique. This novel approach is verified by several waveguide cavity filter designs. The analyzed characteristics of these filters, obtained with commercial full-wave computer-aided-design tools, agree very well with the synthesis results. A third-order filter with one TZ above the passband is designed, fabricated, and measured. Excellent agreement between the measurement and simulation is obtained.     

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.     

Explicit Design Formulas for Waveguide Single-Sided Filters

Explicit formulas are given for the design of optimum single-sided waveguide filters. Using a uniform waveguide with iris-coupled series stubs irregularly spaced along the waveguide, this class of filter results in a significant reduction in the number of resonators required to meet single-passband and single-stopband specifications over conventional techniques. Design information is given for both the Chebyshev and elliptic function cases from which the required structure may be obtained without recourse to synthesis procedures. Computer simulations of the response characteristics of both the quarter- and modified three-quarter-wave coupled quasi low-pass and the quasi high-pass designs are given. Experimental results on fifth-degree Chebyshev filters operating in X band for the former case are presented showing close agreement with theory.     

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.     

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.     

Transmission Characteristics and a Design Method of Transmission-Line Low-Pass Filters with Multiple Pairs of Coincident Zeros and Multiple Pairs of Coincident Poles

The transmission characteristics and a design method are presented for a transmission-line Iow-pass filter with multiple pairs of coincident zeros in the finite frequency of the passband and multiple pairs of coincident poles in the finite frequency of the stopband and for a transmision-line low-pass filter with Butterworth characteristic in the passband and multiple pairs of coincident poles in the finite frequeney of the stopband. The former transmission-line low-pass filter shows an improved skirt attenuation performance and delay characteristic than a Chebyshev transmission-line low-pass filter in the same network degree. The latter type of transmission-line low-pass filter shows an improved skirt attenuation performance in comparison to a Butterworth transmission-line low-pass filter in the same network degree, it is positioned about in the middle between a Butterworth type and a Chebyshev type, the delay characteristic is improved considerably in comparison to the Chebyshev type, and the characteristic is close to that of the Butterworth type. With this design method, the connecting unit elements in addition to the stubs contribute to the attenuation response. The design example is shown on the basis of a concrete specification, and it is shown that the obtained attenuation strictly fulfills the specification.     

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.     

一种新颖的微带带通滤波器的设计

介绍一种选择性介于切比雪夫滤波器与椭圆滤波器之间、物理上也易于实现的带通滤波器,给出了它的传输函数,依此在切比雪夫滤波器设计参数的基础上进行该滤波器的综合,然后用耦合谐振滤波器的理论与公式来分析该滤波器的频率响应。该滤波器采用新颖的开环谐振器耦合结构来实现,结果在保持很好的线性与较高的矩形系数的同时,体积也做得较小。     

OTA-C Filters with Finite Zeros

In this paper we present a novel technique for OTA-C filter realizations with finite zeros based on doubly loaded passive ladder networks. Only grounded capacitors are needed; all floating capacitors are replaced with active simulations eliminating bottom-plate parasitic capacitors and non-observable poles. Bandpass, highpass and bandstop filters are easily obtained from a lowpass OTA-C prototype applying standard frequency transformations that preserve the active simulation of floating capacitors, i.e. the finite zeros realization. Also, we address the high frequency stability problem of highpass and bandstop OTA-C filters simulating doubly loaded passive ladder networks. These filters usually have floating nodes where the OTA excess-phase acting over the nodal parasitic capacitance can introduce unstable poles at high frequencies. The stability problem is fairly the same for highpass and bandstop OTA-C filters based on approximations with and without finite zeros; only the most complex case (filters with finite zeros) will be addressed here.     

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.      

广义切比雪夫波导带阻滤波器设计

广义切比雪夫带阻滤波器含有相移的设计可以使带阻滤波器实现任意位置的反射零点。含有相移的网络在实现之前必须进行优化以减少杂散波的影响,据此从低通原型电路出发,设计制作并测试了一个结构新颖的含有相移的四阶线形带阻滤波器,其中心频率为9.780 GHz,阻带抑制为39 dB,通带中的回波损耗超过18.17 dB。最终的测试和仿真结果证明了这种设计的可行性。     

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.     

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.     

Synthesis of bandpass filters designed on the basis of 1D PBG structures

A technique for the synthesis of bandpass filters designed on the basis of 1D periodic structures with resonant defects is proposed. Conditions under which the filter’s frequency characteristic approaches a Chebyshev characteristic or a maximally flat characteristic are formulated. The synthesis problem is reduced to solution of a system of nonlinear equations. Numerical results are obtained for the particular case of a periodic structure composed of dielectric layers.     

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.     

广义切比雪夫型LC滤波器的设计*

提出一种广义切比雪夫型LC滤波器的设计方法,带外传输零点可以是任意设定,其带外特性既可以对称,也可以不对称.采用此方法设计出的LC滤波器,其带内波动可以与最大平坦型滤波器一样很小,而矩形系数可以与椭圆函数型滤波器一样好.每一个传输零点的位置可以由一个元器件的取值大小控制.与椭圆函数型LC滤波器相比,相同数量的元器件,它可以实现更陡的截止特性.     

Microstrip stepped impedance resonator bandpass filter with an extended optimal rejection bandwidth

Bandpass filters with an optimal rejection bandwidth are designed using parallel-coupled stepped impedance resonators (SIRs). The fundamental (f/sub o/) and higher order resonant harmonics of an SIR are analyzed against the length ratio of the high-Z and low-Z segments. It is found that an optimal length ratio can be obtained for each high-Z to low-Z impedance ratio to maximize the upper rejection bandwidth. A tapped-line input/output structure is exploited to create two extra transmission zeros in the stopband. The singly loaded Q(Q/sub si/) of a tapped SIR is derived. With the aid of Q/sub si/, the two zeros can be independently tuned over a wide frequency range. When the positions of the two zeros are purposely located at the two leading higher order harmonics, the upper rejection band can be greatly extended. Chebyshev bandpass filters with spurious resonances up to 4.4f/sub o/, 6.5f/sub o/, and 8.2f/sub o/ are fabricated and measured to demonstrate the idea.