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.     

Compact Ultra-Wideband Bandpass Filters Using Composite Microstrip–Coplanar-Waveguide Structure

Compact ultra-wideband bandpass filters are proposed based on the composite microstrip–coplanar-waveguide (CPW) structure. In this study, the microstrip–CPW transitions and the CPW shorted stubs are adopted as quasi-lumped-circuit elements for realizing a three-pole high-pass filter prototype. By introducing a cross-coupled capacitance between input and output ports of this high-pass filter and suitably designing the transition stretch stubs, a compact three-pole ultra-wideband bandpass filter is implemented with two transmission zeros located close to the passband edges. To further improve the selectivity, two microstrip shorted stubs are added to implement a five-pole ultra-wideband bandpass filter with good out-of-band response. Being developed from the quasi-lumped elements, and not from the transmission lines, the proposed ultra-wideband filters have sizes more compact than those of the published wideband filters. The proposed ultra-wideband filters have the merits of compact size, flat group delay, good insertion/return loss, and good selectivity. Agreement between simulated and measured responses of these filters is demonstrated.     

Compact microstrip coupled-line bandpass filter with four transmission zeros

A compact coupled-line bandpass filter with multiple capacitive cross-couplings to create four transmission zeros is proposed. The locations of transmission zeros can be adjusted by varying the values of cross-coupled capacitances so as to improve the filter selectivity. The proposed filter is based on one-eighth-wavelength (/spl lambda//8) coupled-line sections and quarter-wavelength (/spl lambda//4) resonators, thus it occupies only half of the circuit area comparing with the conventional coupled-line bandpass filters. Specifically, a fourth-order microstrip coupled-line bandpass filter centered at 2.46GHz with a 3-dB bandwidth of 10.2% and four transmission zeros is implemented and examined.     

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     

A Compact Ultra-Wideband Bandpass Filter Based on Split-Mode Resonator

A compact ultra-wideband (UWB) bandpass filter is proposed based on the coplanar-waveguide (CPW) split-mode resonator. By suitably introducing a short-circuited stub to implement the shunt inductance between two quarter wavelength CPW stepped-impedance resonators, a strong magnetic coupling may be realized so that a CPW split-mode resonator may be constructed. Moreover, by properly designing the dual-metal-plane structure, one may accomplish a microstrip-to-CPW feeding mechanism to provide strong enough capacitive coupling for bandwidth enhancement and also introduce an extra electric coupling between input and output ports so that two transmission zeros may be created for selectivity improvement. The implemented UWB filter shows a fractional bandwidth of 116% and two transmission zeros at 1.705 and 11.39 GHz. Good agreement between simulated and measured responses is observed.     

Novel half-mode substrate integrated waveguide bandpass filters using semi-hexagonal resonators

In this paper, a novel bandpass filter is presented, designed, and implemented by using a triple mode semi-hexagonal Half-Mode Substrate Integrated Waveguide (HMSIW) cavity, which has the advantages of compact size, low insertion loss, and high selectivity in upper and lower passband. To realize a triple mode filter, the first resonant mode is shifted to near the next two modes using a via hole perturbation. Two microstrip open stubs connected to open edge of HMSIW resonator are introduced to generate two transmission zeros in the lower passband. The position of transmission zeros could be controlled by adjusting the coupling gap between the microstrip open stub resonators. By etching an E-shape slot on the top plate of HMSIW resonator, two other transmission zeros are produced in the upper passband. A wide-band planar six-pole bandpass filter, which has the advantages of wide bandwidth and small size, is also proposed and fabricated by cascading two triple mode resonators. Measured results indicate that 29% and 47% fractional bandwidth, as well as approximately 1 dB and 1.1 dB insertion loss, are achieved for the proposed filters. Measured results of all those filters agree well with the simulated results.     

Compact microstrip resonators for 900 MHz frequency band

A technique to reduce the size of planar resonators is investigated using a transmission line model and a finite-difference time-domain (FDTD) method. New miniaturized square microstrip resonators are proposed for 900 MHz band. The resonators offer low impedance sections leading to a better handling of power. The feasibility of compact filters using the proposed resonators is demonstrated. The input/output coupling lines of a two-pole filter have been positioned in a way that produces a filter response with transmission zeros on the both sides of the pass-band. Sharper skirts and higher out-of-band rejection are obtained for four-pole filters with cross-coupled resonators.     

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.     

Modeling of symmetric composite right/left-handed coplanar waveguides with applications to compact bandpass filters

This study proposes an equivalent-circuit model for the composite right/left-handed (CRLH) coplanar waveguide (CPW) comprising the series interdigital capacitor and shunt meandering short-circuited stub inductor in symmetric configuration. The new technique for extracting the equivalent-circuit elements of the CRLH CPW, which include inductances, capacitances, and resistances to represent the left-handed, right-handed, and lossy characteristics, is developed based on the effective medium concept. The applications to the compact resonators and filters are presented to emphasize the unique features of the CRLH CPW. A novel CRLH CPW resonator with a 0/spl deg/ effective electrical length at resonance is proposed, which gives a 49.1% size reduction when compared with the conventional half-wavelength resonator at 5 GHz. Based on the zeroth-order CRLH CPW resonators, an inductively coupled two-pole bandpass filter with 5.4% 3-dB bandwidth and 2.7-dB insertion loss at 5 GHz is implemented, and it is 51.4% more compact than the conventional structure. A good agreement among the results of the full-wave simulation, equivalent-circuit model, published data, and measurement demonstrates the effectiveness of the proposed modeling technique. To suppress the higher order harmonic spurious passbands, the electromagnetic-bandgap CPW structures are incorporated into the proposed CRLH CPW filter.     

Compact Wideband Bandpass Filters Using Stepped-Impedance Resonators and Interdigital Coupling Structures

This letter proposes a microstrip $lambda/4$ interdigital stepped-impedance resonator whose impedance ratio can be very low and coupling strength between adjacent resonators can be very large. On the basis of the proposed structure, one four-pole Chebyshev and one four-pole generalized Chebyshev filter with 0.05 dB equal-ripple bandwidths of 48% and 46%, respectively, are designed and fabricated. Both implemented filters have a compact size, a wide passband, a wide upper stopband, and a high spurious passband at near 5.1 times the center frequency. Good agreement between measurements and simulations is observed.      

Dual-band filter using composite microstrip/CPW structure

A novel and compact dual-band filter using a microstrip/coplanar waveguide (CPW) composite structure is proposed. At the bottom of the substrate material, two CPW open-circuited resonators are broadside-coupled to the top microstrip open-circuited stubs. The proposed filter was designed, fabricated and measured. The obtained frequency responses demonstrated that the filter has good dual-band property.     

Coplanar Waveguide Bandpass Filters With Compact Size and Wide Spurious-Free Stopband Using Electromagnetic Bandgap Resonators

This work presents a novel coplanar waveguide (CPW) bandpass filter (BPF) that uses electromagnetic bandgap (EBG) resonators to reduce the size and suppress the harmonic responses. The propagation characteristic of the EBG structure is investigated by its associated equivalent circuit model. Compared with the conventional half-wavelength resonator at 5GHz, the EBG resonator is 60.5 % more compact. Based on the EBG CPW resonators, the inductively-coupled two-pole BPF with 3.8% 3-dB bandwidth and 2-dB insertion loss at 5GHz is implemented. This structure generates a 59.6% reduction in size and suppresses a second harmonic passband when compared with a conventional filter. To eliminate the third harmonic response, the proposed EBG CPW BPF further incorporates two EBG structures into its input and output ports and has the merit of a small circuit area     

Wide-Stopband Microstrip Bandpass Filters Using Quarter-Wavelength Stepped-Impedance Resonators and Bandstop Embedded Resonators

Novel compact microstrip bandpass filters (BPFs) with extended stopband are proposed using both quarter-wavelength (lambda/4) stepped-impedance resonators and bandstop embedded resonators. First, by properly designing the impedance and length ratios of the stepped-impedance resonators, the developed filter may be made compact and its spurious harmonics may be pushed to the higher frequency region. Next, by suitably designing the bandstop structure so as to suppress the lower spurious harmonics of stepped-impedance resonators and then embedding the bandstop structure into the lambda/4 resonators, one may realize the BPFs with wideband spurious suppression. In particular, by connecting the bandstop embedded resonators to the input/output ports, a compact fourth-order BPF of dimension 0.089 lambdag times 0.27 lambdag is implemented and its stopband is extended up to 8.25 f ₀ with an adequate rejection of greater than 32.49 dB, where f ₀ is the passband center frequency and lambdag is the microstrip guided wavelength at f ₀.     

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。     

Ku 波段微带交叉耦合带通滤波器的结构与设计

基于广义切比雪夫滤波器综合理论,本文设计了一个Ku 波段微带发夹谐振型交叉耦合滤波器。该滤波器的拓扑结构为CQ 型。由于引入非相邻谐振器之间的耦合,在有限频率点处产生传输零点,这样不仅使滤波器具有更好的选择性,而且其结构更加紧凑,尺寸也大大缩小。本文通过HFSS 电磁仿真软件对其进行了优化设计。其仿真结果很好地体现了该滤波器的特性。与同阶数的传统滤波器相比,交叉耦合型滤波器具有更好的带外抑制特性,有较好的工程应用意义。     

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.     

Miniature CPW Parallel-Coupled Bandpass Filter Based on Inductive Loaded Coupled-Lines and Lumped-Element J-Inverters

This study presents a compact coplanar-waveguide (CPW) parallel-coupled bandpass filter (BPF) with good selectivity and stopband rejection. The inductive terminations are introduced to the conventional anti-parallel coupled-lines, and lumped-element J-inverters are employed, to achieve both size reduction and spurious suppression. Additionally, the inductive cross-coupling effect is introduced to obtain two transmission zeros to enhance the selectivity. Suitable equivalent-circuit model is also established as effective design tool. Specifically, this work demonstrates a compact cross-coupled fourth-order BPF in grounded-CPW configuration. Compared to the conventional filters, the proposed filters exhibit over 65% size reduction, improved selectivity, and wider stopbands up to four times the center frequency     

Novel coplanar-waveguide bandpass filters using loaded air-bridge enhanced capacitors and broadside-coupled transition structures for wideband spurious suppression

Novel inline coplanar-waveguide (CPW) bandpass filters composed of quarter-wavelength stepped-impedance resonators are proposed, using loaded air-bridge enhanced capacitors and broadside-coupled microstrip-to-CPW transition structures for both wideband spurious suppression and size miniaturization. First, by suitably designing the loaded capacitor implemented by enhancing the air bridges printed over the CPW structure and the resonator parameters, the lower order spurious passbands of the proposed filter may effectively be suppressed. Next, by adopting the broadside-coupled microstrip-to-CPW transitions as the fed structures to provide required input and output coupling capacitances and high attenuation level in the upper stopband, the filter with suppressed higher order spurious responses may be achieved. In this study, two second- and fourth-order inline bandpass filters with wide rejection band are implemented and thoughtfully examined. Specifically, the proposed second-order filter has its stopband extended up to 13.3f/sub 0/, where f/sub 0/ stands for the passband center frequency, and the fourth-order filter even possesses better stopband up to 19.04f/sub 0/ with a satisfactory rejection greater than 30 dB.     

Novel Multifold Finite-Ground-Width CPW Quarter-Wavelength Filters With Attenuation Poles

This paper proposes a novel multifold finite-ground-width coplanar waveguide (CPW) lambda/4 resonator filter that has the capability of realizing attenuation poles by cross coupling of nonadjacent resonators. The newly proposed multifold structures not only greatly shrink the length of a resonator, but also provide a convenient way to implement cross coupling in a filter. The proposed multifold finite-ground-width CPW resonators can have much stronger coupling than that of spiraling and meandering layouts, and any number of folds is possible. Two combline filters are designed and measured with twofold and threefold lambda/4 finite-ground-width CPW resonators. A trisection and a quadruplet generalized Chebyshev filter formed by cross couplings between nonadjacent resonators have been implemented by modifying the layout of the resonator. These filters are smaller in size and have the capability of controlling attenuation poles     

Ultra-Wideband Bandpass Filter Using Multilayer Liquid-Crystal-Polymer Technology

Novel ultra-wideband (UWB) bandpass filters are proposed based on quasi-lumped-element prototypes and implemented with multilayer liquid-crystal-polymer (LCP) technology. In this study, the broadside-coupled microstrip radial stubs and high-impedance microstrip lines are adopted as quasi-lumped elements for realizing compact UWB bandpass filters. By introducing a short-circuited high-impedance microstrip line as a shunt inductor and suitably designing quasi-lumped-element capacitors, a compact six-pole bandpass filter is implemented with the Federal Communications Commission (FCC) defined UWB specifications. To further improve the selectivity and wideband performance, an eight-pole filter of this type is developed by adding two shunt short-circuited microstrip stubs, which introduce a transmission zero at the upper passband edge. The proposed filters are fabricated using multilayer LCP technology. Good agreement between simulated and measured results of these filters are observed. The measured results show that the fabricated six-pole filter has good specifications for the FCC-defined UWB system. The fabricated eight-pole filter has an ultra-wide fractional bandwidth (139%) and a good stopband rejection level, which is higher than 38.1 dB from 10.57 to 18.0 GHz. The proposed filters are attractive for UWB communications and radar systems.