基于枝节加载开环谐振器的带阻滤波器设计

提出了一种具有良好谐波抑制功能的双枝节加载开环谐振器,加载枝节采用均匀阻抗结构,与同尺寸的开环谐振器相比,结构更紧凑,能够更好地抑制寄生模,而且可以达到更低的谐振频率。分析了加载枝节参数对带阻滤波器抑制二次谐波的影响。通过在加载的双枝节间引入集总可变电容,可以使谐振器具备谐波抑制性能的同时,实现中心频率可调的功能。基于双枝节加载环谐振器设计出一种可调带阻滤波器,中心频率可以在900MHz ~2. 65GHz 范围内调节,而且最低寄生阻带能够抑制到8GHz。     

Dual-Band Filter Design With Flexible Passband Frequency and Bandwidth Selections

In this paper, improved dual-band filter design is studied. The dual-band resonators are composed of shunt open- and short-circuited stubs. In order to fulfil the requirements of dual-band inverters, a structure of stepped-impedance asymmetric coupled lines is proposed and its equivalent circuit is also derived. The dual-band filter is then designed based on this equivalent circuit. This type of filter can achieve relatively large practical passband center frequency ratios (in theory infinite), and it has more freedom of bandwidth ratio. The circuit size is also reduced. Detailed design procedure is presented and, finally, a filter example is given to validate the theoretical study     

Compact Ultra-Wideband Microstrip/Coplanar Waveguide Bandpass Filter

A novel ultra wideband (UWB) bandpass filter is presented, using a compact coupled microstrip/coplanar waveguide (CPW) structure. The filter comprises of a single CPW quarter-wavelength resonator which is coupled to two microstrip open-circuited stubs on the other side of a common substrate. The two microstrip open-circuited stubs, which are about a quarter-wavelength long at the center frequency, can function as two resonators with associated coupling arrangement to the CPW. This forms a very compact three-pole filter. The proposed filter also exhibits a quasi-elliptic function response, with one finite-frequency transmission zero closer to each side of the passband. Thus, a high selectivity is achieved using a small number of resonators, which leads to low insertion loss and group delay across the passband. The performance is predicated using EM simulations and verified experimentally. The experimental filter shows a fractional bandwidth of 90% at a center frequency of 6.4GHz, with two observable transmission zeros (attenuation poles) at 1.95 and 10.36GHz, respectively. Furthermore, it has a very small size only amounting to 0.25 by 0.08 guided wavelength at the center frequency     

Direct-coupled microwave filters with single and dual stopbands

This paper presents new ideas for the design and implementation of microwave filters with single and dual stopbands. They can be realized with waveguide, coaxial, dielectric resonators, or in a planar technology. The new methods represent an advance over present methods in that the resonators are direct coupled, thus avoiding the need for transmission line phase lengths between resonator stubs that tend to degrade performance due to their dispersion and are difficult to adjust during tuning. Three bandstop (BS) configurations are presented. The first will accommodate even or odd characteristics and also asymmetric responses, although some negative or diagonal cross-couplings will be needed. The second resembles the cul-de-sac configuration for bandpass filters and needs no diagonal or negative couplings even for asymmetric characteristics. The third is an application of the cul-de-sac synthesis technique to dual-band bandstop (DBBS) filters. All these BS designs are very similar to regular bandpass filters in their design and realization. The design of a DBBS filter is presented and compared with an equivalent bandpass filter to demonstrate its advantages. Finally, the simulated and measured results of a fourth-degree BS filter design in the novel cul-de-sac configuration are presented.     

Combline filters designed on symmetric stripline

Problems arising during the design of stripline combline filters, which until quite recently were considered as all-stop microwave structures, are considered. It has been shown that the electromagnetic coupling coefficient of quarter-wave stripline resonators increases with the value of material permittivity ε_r, the operating frequency, and the thickness of the filter resonators. For ε_r = 92 and a thickness of stripline resonators of 4 mm, it exceeds 12% at frequencies higher than 2.2 GHz. Two alternative versions of combline filters have been designed: a filter with a coupling strip and a filter without a coupling strip. Experimental data for a nine-resonator combline filter with a thickness of 4 mm, ε_r = 9.7, and the center frequency f ₀ = 2.4 GHz are presented. A method for increasing the selectivity of combline filters with the same number of resonators is proposed. It has been found that amplitude–frequency responses of stripline combline filters are near-symmetric, unlike the responses of microstrip combline filters.     

Narrow bandpass filters using dual-behavior resonators

This paper reports on a new concept of narrow bandpass filters leading to perfectly controlled electrical responses within both the required operating bandwidth and adjacent undesired bands. A specific topology is considered for such a "global synthesis": in comparison with conventional filter performances, it provides significant improvements in terms of rejection control. The attenuated frequencies are each located apart from the bandpass frequencies and controlled by means of n transmission zeros introduced through original dual-behavior resonators (DBRs). These resonators are based on the association of different parallel open-ended stubs and allow the designer to independently control the in-band and out-of-band responses of the filter. A global synthesis approach is also discussed on a simplified architecture based on stepped impedance stubs, and the experimental results shown clearly validate the proposed concept. This simplification reduces the number of degrees of freedom when designing a DBR, and consequently the two transmission zeros become dependent.     

960 MHz同轴介质谐振器滤波器的研制

研制了用四个高Q值介质同轴谐振器构成的带通滤波器,谐振器之间的耦合通过陶瓷基片上的电容实现,讨论了影响谐振器插入损耗的主要因素。结果表明,该四级式低损耗介质同轴谐振器滤波器中心频率f0为960MHz,插入损耗小于3.0dB,能满足设计要求。     

Magnetically Tunable Band-Stop Filters

Techniques for the design of magnetically tunable band-stop filters using ferrimagnetic garnet resonators (such as yttrium-iron-garnet spheres) are presented. Design for prescribed response, starting from a low-pass lumped-element prototype filter is outlined. The filter structure consists of a strip line or waveguide with garnet spheres mounted at intervals of approximately a one-quarter-wavelength or three-quarters-wavelength, at the center of the tuning range. Tuning is achieved by varying a biasing magnetic field. Techniques for enhancing the coupling to the garnet-sphere resonators are discussed, and the results of four trial designs which verify the theory are presented. The band-stop filter techniques are shown to also provide a very simple means for measuring the ferrimagnetic resonance linewidth /spl Delta/H of garnet spheres.     

一种基于互异结构的宽阻带带通滤波器研究

针对带通滤波器的高次谐波干扰,结合目前常用的在输入输出微带馈线上添加开路线构成带阻的方法,采用两个互异的中间添加开路线的阶跃阻抗开环谐振器来实现高次谐振频点的相互分离,达到抑制高次谐波实现宽阻带的目的。通过仿真软件对这一方案的验证及网络分析仪的实物测试证明,该方案具有良好的效果,能广泛应用于带通滤波器的谐波抑制。     

Serially-connected series-stub resonators for narrowband coplanar-stripline bandpass filters

In this letter, a coplanar stripline (CPS) series resonator composed of serially-connected series-stubs is proposed. This kind of resonator provides two transmission zeros close to the resonant frequency. With the proposed structure, the reactance slope parameters of the resonators are significantly increased and adjustable by changing the length ratio of the two series stubs. This is useful for designing narrowband filters which is difficult to realize with conventional series CPS resonators. The structures of the resonators are optimized for a lower radiation loss and used to design a narrowband Chebyshev bandpass filter. The simulation and experimental results show that the proposed filter provides multiple transmission zeros and high selectivity.     

Planar filter design with fully controllable second passband

New designs of the dual-band filter realized by distributed circuits are studied in this paper. Series and parallel open stubs are used as the resonators to fulfil the dual-band characteristics. Two dual-band inverters are proposed, which can be easily merged with adjacent resonators to reduce the circuit size. All the theoretical analysis and design procedures are discussed in detail and have been successfully verified by experiment results.     

Tunable, temperature-compensated dielectric resonators and filters

A thermal and electromagnetic model of a tunable hybrid-mode dielectric double resonator is introduced and analyzed by the mode-matching technique. Results of the analysis show the temperature sensitivity of the structure as a function of the center frequency as well as the other resonator parameters. A simple optimization procedure which allows the design of the resonator to have both a wide tunability range and good thermal stability of the resonant frequency is described. A circuit model is presented for a tunable four-pole dual-mode filter. The model exhibits interesting dual passbands, separated by a very-high-attenuation stopband. Measured results obtained from an experimental four-pole dual-mode dielectric resonator filter designed using the tunable hybrid-mode resonators showed excellent tunability range (200 MHz at C-band) and good agreement with the circuit model     

Novel Broadside-Coupled Bandpass Filters Using Both Microstrip and Coplanar-Waveguide Resonators

Novel quasi-elliptic coupled-resonator bandpass filters with wider fractional bandwidth are proposed. By using the broadside-coupled mechanism to couple the half-wavelength microstrip resonators and the quarter-wavelength coplanar-waveguide (CPW) resonators together with introducing two CPW shorted stubs, the required mixed and magnetic couplings associated with the resonators may be enhanced so that a wider bandwidth cross-coupled filter may be realized. Specifically, a fourth-order quasi-elliptic broadside-coupled bandpass filter with a center frequency at$f _0 =1.48~hboxGHz$, a minimum insertion loss of 0.68 dB, and a wider 3-dB fractional bandwidth of 34.6% is implemented, and its stopband is extended up to 6 GHz$(4f _0)$with a rejection better than 20 dB.     

Synthesis of dual-band bandpass filters using successive frequency transformations and circuit conversions

A novel method is proposed to synthesize dual-band bandpass filters (BPFs) from a prototype low-pass filter. By implementing successive frequency transformations and circuit conversions, a new filter topology is obtained which consists of only admittance inverters and series resonators, and is thereby easy to be realized by using conventional distributed elements. A dual-band BPF with center frequencies of 1.8GHz and 2.4GHz is designed and fabricated using microstrip lines and stubs. The simulated and measured results show a good agreement and validate the proposed theory.     

Waveguide Bandstop Elliptic Function Filters

Using the "natural prototype" for elliptic function filters, a design procedure is presented for a class of waveguide bandstop filters, which exhibit equiripple passband and stopband responses. Due to the availability of explicit formulas for element values in the natural prototype elliptic function filter, the design procedure is entirely analytic and does not require numerical synthesis techniques. The resulting physical structure is the familiar uniform guide with iris-coupled series stubs. Unlike the bandstop filters designed from maximally flat or Chebyshev prototypes, the elliptic function design results in stubs that are not exactly three-quarter-wave coupled.     

厘米波段介质带通滤波器的设计与制作

为了提高基站的通信质量,研制了高性能的窄带介质带通滤波器。选择切比雪夫低通原型设计线路,采用6个环形介质谐振器直接耦合实现滤波器,输入输出采用探针耦合。用HFSS软件对滤波器的结构进行了仿真。用εr=38的高Q值介质陶瓷材料制作了环形谐振器,分析了衬垫材料的高度对环形谐振器性能的影响,测试了级间耦合系数。最后制作出中心频率为6GHz的介质带通滤波器,滤波器的带宽窄（0.5%）,插入损耗较小,阻带衰减很高,达到了国内先进水平。     

Compact (<0.5mm2) K-band metamaterial bandpass filter in MCM-D technology

A bandpass filter based on complementary split ring resonators (CSRRs) and implemented in MCM-D technology is presented for the first time. It is a thin-film microstrip structure with CSRRs etched in the ground plane and interdigital capacitors in the signal strip. In addition, the structure includes grounded stubs. The combination of CSRRs and such stubs is useful to generate a transmission zero above the left-hand passband of the filter, and thus improve frequency selectivity. The filter, consisting of two CSRR cells, has a central frequency of f_o=19 GHz and a fractional bandwidth of FWB=18%. Inband return losses (RL=-15 dB) are satisfactory, while insertion losses (IL=-7.4 dB) are affected by the very small size of the resonant elements. Filter size is as small as 918times450 mum, i.e. 0.094 lambda_gtimes0.045lambda_g, where lambda_g is the guided wavelength at f_o. The implementation of these metamaterial-based structures in MCM-D technology opens new directions for the synthesis of ultra-small filters operating at millimetre wavelengths     

Parallel-coupled line filters with enhanced stopband performances

A new class of parallel-coupled line filters with broad stopband response is introduced. The design is based on the synthesis of bandpass prototypes with pre-defined upper stopband characteristics. The new filters have uniform- and stepped-impedance resonators, some of which are loaded by open-circuited stubs at their open-circuited ends. A seventh-order filter implementation is presented with a fundamental passband centered at 1 GHz. The measured wide-band transmission characteristic of the filter demonstrated a broad upper stopband and was in agreement with simulations. The performance of the new filter is also compared with the characteristic of a conventionally designed filter to highlight the advantages of the proposed design method.     

Design of Composite Right/Left-Handed Coplanar-Waveguide Bandpass and Dual-Passband Filters

The design and implementation of novel coplanar-waveguide (CPW) bandpass and dual-passband filters that consist of the composite right/left-handed short-circuited stubs are proposed. In contrast to the conventional short-circuited stub, whose input impedance repeats every half-wavelength, the composite right/left-handed CPW stub combines the phase-lead composite right/left-handed CPW and the phase-lag uniform CPW to achieve the arbitrary resonant frequencies with compact size. The equivalent bandpass and dual-passband LC resonators are established by investigating the frequency responses of the composite right/left-handed CPW stubs. The composite right/left-handed CPW bandpass filter is 62.5% more compact than the conventional quarter-wavelength shunt-stub CPW bandpass filter. The composite right/left-handed CPW dual-passband filter, which possesses the sharp rejection between the two asymmetric passbands, is also developed. The synthesis procedures of the composite right/left-handed CPW bandpass and dual-passband filters are successfully validated by measurement and full-wave simulation.     

Compact, low insertion loss, sharp rejection wideband bandpassfilters using dual-mode ring resonators with tuning stubs

Novel wideband bandpass filters using dual-mode ring resonators with orthogonal direct-connected feed lines and tuning stubs are developed. The tuning stubs act as series resonators and provide sharp rejections for the filters. Also, a perturbation stub in each ring influences the fields of the ring resonators and generates a dual mode to extend the stop bands of the filters. The simulated and measured results agree well. This novel bandpass filter has advantages of compact size, low insertion loss, and sharp rejection