Design of Stepped-Impedance Combline Bandpass Filters With Symmetric Insertion-Loss Response and Wide Stopband Range

An enhanced stepped-impedance combline bandpass filter employs an array of stepped-impedance resonators with tapped-transformer coupling at input and output is presented in this study. This filter has enhanced performance, including symmetric insertion-loss response around the passband and wider stopband range. The structure is compact and suitable for multilayer realization because it is free of lumped capacitors and has fewer via-hole grounds. The circuit is investigated with the characteristic mode theory of coupled lines to prove the existence of multiple transmission zeros around the passband. Numerous diagrams are given for circuit design purposes. The second- and fourth-order bandpass filters at 2.45 GHz were designed, measured, and compared with the conventional combline structure to demonstrate their performance enhancement.     

At least N+1 finite transmission zeros using frequency-variant negative source-load coupling

A second-order cross-coupled combline filter which has three finite transmission zeros is presented. The problem of the frequency-invariant coupling in a real circuit is introduced. To make extra transmission zeros, a top metalized dielectric block is used.     

Two-Cavity Filter With Three Transmission Zeros

It is well known that an N-order coupling network with source-load coupling can realize a maximum number of transmission zeros equal to N. However, in the letter, by utilizing open-circuited stubs and increasing the velocity ratio, a novel two-pole hairpin filter can obtain three transmission zeros, which can improve selectivity in the lower stopband. The filter is analyzed extensively by using the relations between the types of coupled microstrip lines and transmission zeros of transfer response. Good agreement between measured and simulated data has been demonstrated.     

Realization of transmission zeros in combline filters using an auxiliary inductively coupled ground plane

The out-band transmission zeros of the multilayer low-temperature co-fired ceramic bandpass filter are studied. The design target of this filter, with passband between 2.3-2.65 GHz (the true application is 2.4-2.483 GHz), is to reject the local oscillator and image signals and, in the mean time, to suppress the harmonic frequency. This filter is a modified three-pole combline filter, which can easily achieve a high rejection rate and low insertion loss. The source-load coupling capacitor incorporation with cross-coupling grounding inductors can generate three transmission zeros. By properly adjusting the inductance values of the inductors between three resonators and ground the transmission zero can easily be manipulated at a high-side skirt to suppress the harmonic frequency. The measured results match well with the electromagnetic simulation that provides evidence for the feasibility of the proposed design.     

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.     

具有传输零点的片式LTCC滤波器的设计与实现

带通滤波器是无线通信中重要的元器件之一,其小型化具有重要意义.研究设计了一种改进型的梳状线LTCC滤波器.在一般抽头式梳状线滤波器设计的基础上,通过增加输入输出级之间的交叉耦合,引入了传输零点,并结合电路仿真以及三维电磁场仿真,辅之以DOE(design of experiment)的设计方法,设计出了一种高抑制、低插损的滤波器,实际测试结果与仿真结果吻合较好.由于采用了LTCC多层结构,该滤波器体积非常小,是标准的片式元器件封装.具有较强的实用性.     

A Dual-Band Combline Bandpass Filter Loaded by Lumped Series Resonators

This letter presents a dual-band combline bandpass filter (BPF) loaded by lumped series resonators. The proposed filter configuration can easily generate two desired passbands by controlling the resonant frequencies of the comblines as well as the series resonators. Furthermore, the skirt frequency characteristics between the two passbands are improved by transmission zeros introduced by source-load coupling via a lumped element capacitor. Two-pole dual-BPF with center frequencies of 1.2 and 1.54 GHz is designed and the measured results agree well with simulated results.     

多传输零点LTCC梳状线带通滤波器的设计与实现

设计了一种改进型的梳状线LTCC滤波器.在一般抽头式梳状线滤波器设计的基础上,结合电路仿真以及三维电磁场仿真,辅之以DOE(design of experiment)的设计方法,设计出一种高抑制、低插损多传输零点的滤波器.滤波器的实际实现采用在当今射频通信器件设计中流行的LTCC技术.该滤波器中心频率为2.45GHz,带宽150MHz,可以广泛运用于无绳电话、蓝牙模块,以及WLAN的射频电路中.     

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.     

Varactor-tuned combline bandpass filter using step-impedance microstrip lines

In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constant within the tuning range. The difference between the odd- and even-mode characteristics of the coupled microstrip line makes it difficult to design a tunable bandpass filter with minimum degradation in passband performance. By using step-impedance microstrip lines, couplings between resonators can be controlled so that the constant bandwidth requirement could be satisfied with reasonable design parameter values. Lumped inductors are used for input and output coupling networks. Design equations are derived, and experimental results are compared with theoretical ones based on these equations.     

一种新型传输零点可控的微带带通滤波器

提出了一种新型的传输零点可控的微带带通滤波器结构,它由一段低阻抗线和与之相连的平行耦合线构成。通过调节低阻抗线与平行耦合线的偶模阻抗比,可以改变谐振器的2个模式之间的距离,从而灵活的调节滤波器的带宽;而通过调节平行耦合线的间距,则可以方便的调节传输零点的位置。仿真与实测结果都表明该滤波器具有良好的性能：低插损,结构紧凑,可以灵活的调节带宽和传输零点的位置。     

多带外传输零点微带带通滤波器设计

设计了一种梳状微带平行耦合线窄带带通滤波器,仅应用两腔结构就实现了带外5个传输零点.通过微带线开路枝节,平行耦合线结构,以及馈电位置和两个梳状线谐振器之间的耦合,在通带附近引入了3个传输零点;四分之一波长平行耦合线接地短路结构,在带外高频产生额外两个传输零点,进而可有效抑制零点频率附近的杂波干扰.实测结果表明,设计的滤...     

Modified parallel-coupled filter with two independently controllable upper stopband transmission zeros

A microstrip cross-coupled filter with two independently controllable transmission zeros on upper stopband is presented. The initial filter structure is a conventional Chebyshev-response parallel-coupled filter that can be easily realized by the analytical method. The newly proposed coupling/shielding lines can effectively control the cross and main couplings without changing the original filter layout. This approach allows a designer to eliminate the tedious segmentation method, which is usually used to establish the relation between the coupling coefficient and physical distance between resonators. A three-order filter is designed and fabricated for demonstration.     

微带交叉耦合滤波器的简化设计

主要研究微带交叉耦合滤波器的简化设计。通过约束传输零点之间的关系,简化了带通滤波器交差耦合的拓扑结构,同时又较好保持了带通滤波器带外的抑制能力。在利用微带结构实现时,采用了谐振器顺序耦合的结构,降低了滤波器微调的难度。同时在第一和第四谐振器间增加一段传输线以引入交叉耦合,通过调整引入传输线的位置等可调整相应传输零点的位置,增加了滤波器设计的灵活性。仿真结果验证了相关方法的有效性。     

A Narrow Bandwidth Microstrip Band‐Pass Filter with Symmetrical Frequency Characteristics

This letter proposes a band‐pass filter (BPF) with two transmission zeros based on a combination of parallel coupling and end coupling of half‐wave transmission lines. The fabricated BPF exhibited a narrow bandwidth and two transmission zeros near the pass‐band due to the end‐coupled and shielding waveguide. At the center operation frequency of 60 GHz, the 20 dB bandwidth of the BPF is 1.0 GHz, which is almost 2% of the center operation frequency, and the insertion loss is 3.12 dB. Two transmission zeros reach approximately 40 dB at 58.5 and 62.5 GHz. The simulation results almost agree with the measured results.     

Design of multilayered broadband bandpass filter with LTCC technology

With two pairs of asymmetrical feeding short-circuit coupled lines, a multilayered broadband bandpass filter is proposed and constructed. To enhance the selectivity of the passband two pairs of coupled lines need to be properly connected with both inductive and capacitive coupling to generate two transmission zeros at both sides of the passband skirts. Measured results show a bandwidth ratio of the passband of more than 44.6% when its centre frequency is 3.875 GHz.     

Multiway uniform combline directional couplers for microwavefrequencies

An improved optimization technique for multiway uniform forward-directional couplers is presented using a previously published matrix theory of coupled transmission lines. With the help of this computer optimization method, microwave mode-interference combline directional couplers having an arbitrary number of lines can be designed for arbitrary power distribution. Theoretical designs ranging from two-way to nine-way couplers have been tested with success. The observed behavior of some of these couplers is briefly discussed. Typically these couplers exhibited octave bandwidth. A five-way design example of an equal power splitting combline coupler was fabricated using an open microstrip configuration for operation within 1.6-3.2 GHz. The measured characteristics show good agreement with the computed values     

一种改变交叉耦合极性的新方法

提出了一种用传输线在微带交叉滤波器和腔体交叉滤波器中实现交叉耦合极性改变的新方法。在微带交叉耦合滤波器中运用180°电长度的传输线实现源与非相邻谐振器的耦合,可使交叉耦合极性由容性变为感性。在腔体交叉耦合滤波器中,使用180°左右电长度的传输线,可使传输零点从阻带高端移动到阻带低端。讨论了不同电长度的传输线对交叉耦合的影响,通过调节传输线的电长度,控制传输零点的位置,提高滤波器的带外抑制。这种改变耦合极性的方法,可以用同一耦合方式获得任意位置的传输零点,给滤波器设计提供了更大的自由度。     

广义切比雪夫滤波器综合的统一理论

无线通信系统需要高性能的交叉耦合滤波器.交叉耦合滤波器的综合从给定的传输零点和回波损耗出发,直到得到各腔体之间的耦合系数.该文介绍在同一电路拓扑结构下提取耦合矩阵的统一理论,可同时实现带通和带阻滤波器的综合方法.     

Miniature Dual-Band Filter Using Quarter Wavelength Stepped Impedance Resonators

A miniature dual-band filter using quarter wavelength (lambda_g/4) stepped impedance resonators (SIRs) is proposed. Short and open SIRs are coupled together to realize lower and upper passbands, respectively. Miniaturization is achieved due to the use of lambda_g/4 resonators and a combline coupling structure. Two transmission zeros in a mid-stopband and one in each lower and upper stopbands are achieved. In order to see the capability of this structure to achieve different second passband frequencies, two dual band filters at frequencies of 2.45/5.25 GHz and 2.45/5.75 GHz are realized. Measured insertion losses are 1.3 dB and 2.3 dB and return losses are better than 17 dB and 18 dB at the first and second passband frequencies, respectively, with a mid-stopband attenuation better than 30 dB. The size of the filter is as compact as 19.0 times 5.2 mm² on a RO 4003C (epsiv_r = 3.38, h = 0.81 mm) substrate.