Coupling-Matrix Design of Dual and Triple Passband Filters

The concept of the conventional coupling matrix is extended to include designs of dual- and triple-band filters. The multiband response is created by either placing transmission zeros within the bandwidth of a wideband filter or using higher order resonances. Realizable topologies both in planar and waveguide technologies can be imposed and associated coupling coefficients enforced during optimization. The design process is verified by measurements and comparison with results of commercially available field solvers     

带DGS结构的宽带微带线准椭圆函数滤波器设计

准椭圆滤波器体积小，重量轻，结构紧凑，比契比雪夫滤波器有更好的过渡特性，更高的带外抑制，在卫星通信和移动通信中有广泛的应用前景。但在用准椭圆滤波器实现宽带滤波器时，有时会遇到耦合间隙过小难以加工的问题。在准椭圆滤波器的谐振器底板加入缺陷接地结构（DGS），可以增强谐振器之间的耦合。应用DGS结构，用较宽的耦合间隙实现较强的耦合，从而使宽带滤波器物理上更容易实现。应用三维电磁场仿真软件，设计了一种带DGS结构的宽带微带线准椭圆函数滤波器。     

通带耦合特性独立可调的双频微带滤波器设计

引入一种新型双通带滤波器耦合结构,采用微带线型SIR结构分别设计了切比雪夫型和准椭圆函数型2.4GHz/5.2GHz双频带通滤波器。运用电磁数值分析软件讨论了结构参数对双通带滤波器耦合性能的影响,以及准椭圆函数型滤波器耦合结构参数对其传输零点位置的影响,并在文中给出其变化规律。基于该耦合结构的新型双频带滤波器,设计自由度更高,两个通带所需耦合系数可以独立调节。根据以上结构参数所制备的样品,其性能测试结果与仿真结果吻合良好。     

Design of microstrip bandpass filters with multiorder spurious-mode suppression

This paper proposes a bandpass filter design method for suppressing spurious responses in the stopband by choosing the constitutive resonators with the same fundamental frequency, but staggered higher order resonant frequencies. The design concept is demonstrated by a four-pole parallel-coupled Chebyshev bandpass filter and a compact four-pole cross-coupled elliptic-type bandpass filter. Each filter is composed of four different stepped-impedance resonators (SIRs) for which a general design guideline has been provided in order to have the same fundamental frequency and different spurious frequencies by proper adjusting the impedance and length ratios of the SIR. Being based on knowledge of the coupling coefficients and following the traditional design procedure, the resultant filter structures are simple and easy to synthesize. The measured results are in good agreement with the simulated predictions, showing that better than -30-dB rejection levels in the stopband up to 5.4f/sub 0/ and 8.2f/sub 0/ are achieved by the Chebyshev and quasi-elliptic filters, respectively.     

The design of microstrip six-pole quasi-elliptic filter with linearphase response using extracted-pole technique

The development of microstrip filters has been in great demand due to the rapid growth of wireless communication systems in this decade. Quasi-elliptic response filters are very popular in communication systems because of their high selectivity, which is introduced by a pair of transmission zeros. A number of ways of implementing the quasi-elliptic response filter on microstrip have been studied over the last two decades, i.e., the cascaded quadruplet filter, canonical filter, and extracted-pole filter. However, there is very little information in the literature giving the design details for microstrip extracted-pole filters. In this paper, design equations of the extracted-pole filter for microstrip are reviewed. A new class of microstrip filter is also presented here. This class of filter will have a quasi-elliptic function response and at the same time linear phase in the passband. The linear phase of the filter is introduced by an in-phase cross coupling, while the transmission zero is realized using an extracted-pole technique. Experimental results, together with a theoretical comparison between the group delay of this design, and the conventional quasi-elliptic six-pole filter are also presented     

Computer-Aided Filter Alignment and Diagnosis

The cavity resonant frequencies and coupling values of a wide range of bandpass filters, band-reject filters, and equalizers have been determined in situ by computer-adjusting analytic models to fit the scattering parameters measured on an automatic network analyzer. A higher order mode elliptic filter, a dual-mode quasi-elliptic filter, and a dual-mode band-reject filter are presented as examples. The general relationships between mechanical dimensions and circuit parameters are discussed. The circuit adjustment procedure is outlined, and equations for the sensitivity coefficients of several element types are tabulated.     

Dual-Band Dielectric-Resonator Filters

A novel dual-band dielectric resonator constructed from a single piece of high-$K$ ceramic substrate is presented in this paper. The proposed dual-band dielectric resonator is employed to implement dual-band filters whose center frequencies and bandwidths of the first and second passbands can be controlled independently. To illustrate the concept, two dual-band filters of this type with different bandwidth and separation of two passbands are designed, fabricated, and measured. The filters are both compact in size with a great simplicity in assembly and integration. The developed dual-band dielectric-resonator filters are potentially applicable for multiband applications in future wireless communication systems.      

基于频率变换的双通带腔体滤波器的研究

该文基于频率变换的方法设计了两种结构的双通带的腔体滤波器,一种是通过谐振器之间直接耦合实现的;另一种是在谐振器之间引入交叉耦合实现的,从而达到产生传输零点的目的。首先根据设计指标,采用频率变换的方法,计算得到谐振器间的耦合系数和外部Q值,然后利用Ansoft HFSS建立同轴腔体滤波器的模型并进行仿真,仿真结果与ADS中等效电路得到的理论结果基本吻合,从而验证了这种方法的正确性。最后通过对级联型结构与交叉耦合型结构双通带腔体滤波器的比较,得出后者比前者具有更好的带外抑制特性。     

Miniature high-Q double-spiral slot-line resonator filters

A new class of low insertion-loss miniaturized filters using slot-line resonators is proposed. Miniaturization is achieved by terminating the slot line with a double-spiral inductive termination at both ends. Using this miniaturized resonator, both positive and negative couplings may be realized, and therefore, both standard coupled-line and cross-coupled quasi-elliptic filters are realizable. The unloaded Q of these slot-line filters is considerably higher than that of miniaturized microstrip filters of comparable dimensions due to the inherent higher Q of the slot line. To demonstrate the validity of the design procedures and the performance characteristics, two different types of filters were fabricated and tested. One is a four-pole Chebyshev filter and the other is a quasi-elliptic filter where, in each case, the full-wave simulations show very good agreement with measurements.     

A Quasi-Elliptic Function Dual-Band Bandpass Filter Stacking Spiral-Shaped CPW Defected Ground Structure and Back-Side Coupled Strip Lines

A quasi-elliptic function dual-band bandpass filter (BPF) stacking spiral-shaped coplanar waveguide defected ground structure and back-side coupled strip lines is proposed, which allow two transmission paths to radio frequency signals. Each of them has quasi-elliptic characteristics and results in a respective passband. This can provide convenience to change one passband operating frequency independently of the other one. Several attenuation poles in the stopband are realized to improve the selectivity of the proposed BPF. Theoretical and experimental results with good agreement are presented     

Novel Dual-Mode Dual-Band Filters Using Coplanar-Waveguide-Fed Ring Resonators

This paper presents a novel approach for designing dual-mode dual-band bandpass filters with independently controlled center frequencies and bandwidths. Two microstrip perturbed ring resonators are employed to obtain dual-mode dual-band responses. Novel feeding structures are introduced to simultaneously feed the ring resonators and conveniently control the coupling strength between resonators and feeding lines, resulting in a wide tunable range of external quality factors. Two kinds of filter configurations with compact size are proposed. Both of them provide sufficient degrees of freedom to satisfy various requirements of external qualify factors and coupling coefficients at both passbands. Therefore, the center frequencies and fractional bandwidths of both passbands can be independently tuned to desired specifications within a wide range. To verify the proposed method, four filters are implemented. The measured results exhibit dual-mode dual-band bandpass responses with high selectivity.     

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.     

A Dual-Band Coupled-Line Balun Filter

In this paper, a new type of device called dual-band coupled-line bandpass balun filter is presented. Based on the traditional coupled-line filter theory and Marchand balun configuration, a new device with both filter-type, as well as balun-type characteristics is proposed. The new device utilizes -type transmission-line stepped-impedance resonators to achieve a dual-band operation. Besides providing a simple design procedure for the device, its working mechanism is also revealed mathematically. A prototype balun filter operating at 2.4 and 5.8 GHz has been realized using traditional printed circuit board technology to validate the proposed concept and theory, showing promising application potentials for future multiband RF wireless transceiver modules. Experimental measurements show good agreement with analytical and computer simulations.     

基于非对称共地λ/4谐振器对的三频带滤波器设计

提出了一种全新的谐振器结构——非对称共地λ/4谐振器对。此谐振器对由一个λ/4 UIR谐振器和λ/4 SIR谐振器通过共用一个接地通孔组合而成。其中SIR谐振器工作于2.4 GHz与5.2 GHz频段,UIR谐振器工作于3.6 GHz频段,据此设计制作了一个四级三频带切比雪夫型滤波器并进行了测试和仿真。结果表明,该滤波器的测试结果与仿真符合良好。利用此谐振器对设计的滤波器不仅体积大大减小,而且每个通带的位置及其耦合特性都能够独立调谐。     

基于非对称共地λ/4谐振器对的三频带滤波器设计

提出了一种全新的谐振器结构——非对称共地λ/4谐振器对.此谐振器对由一个4 UIR谐振器和λ/4 SIR谐振器通过共用一个接地通孔组合而成.其中SIR谐振器工作于2.4 GHz与5.2 GHz频段,UIR谐振器工作于3.6 GHz频段,据此设计制作了一个四级三频带切比雪夫型滤波器并进行了测试和仿真.结果表明,该滤波器的测试结果与仿真符合良好.利用此谐振器对设计的滤波器不仅体积大大减小,而且每个通带的位置及其耦合特性都能够独立调谐.     

A simple and effective method for microstrip dual-band filters design

A new type of novel low loss dual-band microstrip filters using folded open-loop ring resonators (OLRRs) is presented in this letter. Both magnetic and electric coupling structures are implemented to provide high performance passband response. The first passband and second passband of the designed dual-band filter can be easily and accurately shifted to a desired frequency band by adjusting the physical dimensions of OLRRs. Finally, the 2.4-GHz/5.7-GHz and 2.4-GHz/5.2-GHz dual-band filters are illustrated and measured in this letter.     

Differential evolution strategy cum equivalent circuit method for the design of multi-band frequency selective surfaces

The paper presents the design of multiband frequency selective surfaces (FSS) using the differential evolution strategy (DES) cum equivalent circuit method (ECM). Two examples are demonstrated to design a dual-band gridded-square and a triple-band gridded-double-square array respectively. Good agreements are obtained between the simulation results and experimental results. The good results under very short computational time and none trial-and-error procedure demonstrate the feasibility of the proposed method.     

Quasi-elliptic compact high-power notch filters using a mixedlumped and distributed circuit

A quasi-elliptic notch filter response is defined as one in which the ultimate stopband depth is sacrificed in favor of a faster transition from the passband to a specified minimum equiripple stopband attenuation level (i.e., steeper attenuation slope) with no increase in filter order (as compared to a Chebyshev or similar transfer function design). Such notch-filter responses can be achieved if the topology synthesized includes arbitrary frequency invariant impedances and line lengths in the main series line of filters. Using lumped approximations to the series coaxial sections but with the series sections not at 50 Ω (for a 50-Ω filter), it is possible to improve upon the Chebyshev-based results. The resulting network provides lower passband insertion loss, with no reduction in minimum notch depth or power handling, improved temperature performance and additional harmonic reduction. The improvements are due to the implementation of the quasi-elliptic response defined above, and are made possible by the larger range of main line impedances and line lengths available using inductors and capacitors rather than lengths of transmission line. In principle, the technique can be extended to achieve full-elliptic responses     

Dual-Band Vertically Stacked Laminated Waveguide Filter Design in LTCC Technology

A new design method of dual-band filters with laminated waveguide (or substrate integrated waveguide) is proposed by taking advantage of the existence of multiple cavity modes. The major design concept is adequately choosing geometric shape of laminated waveguide resonators to control the frequency bands, and positions of open slots and feeding probes to realize the desired coupling coefficients and external quality factors at both bands simultaneously. Two design examples with third-order and quasi-elliptic filter responses are given and verified by experiments. By using the low-temperature co-fired ceramic technology, the laminated waveguide resonators are vertically stacked, and the filter size can be miniaturized.      

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.