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This document presents a dual-band bandpass filter with fully independent passbands. The filter is based on a novel dual-band resonant junction (DBRJ) and λ/2 resonators. This approach allows different filter order at each passband, independent fractional bandwidth tuning, and independent filter response at each band. The DBRJs consist of a short-circuited quarter-wavelength resonator. One prototype is presented with Butterworth and Chebyshev responses and center frequencies at 1.8 and 2.45 GHz.

In this paper, we describe a method to implement compact multiband bandpass filters with suppression of second harmonic frequency. This filter design approach is based on decreasing the coupling gap between adjacent resonators of a parallel-coupled-line bandpass filter in order to achieve both the desired multiband frequency response and the spurious suppression. We present the theoretical analysis of the proposed structure that consists of modeling the frequency dependence of the even- and odd-mode characteristic impedances as well as due to the different phase velocities of the parallel-coupled microstrip lines. As an example, a compact tri-band parallel-coupled-line bandpass filter with suppression of second harmonic frequency was implemented operating at 1.9/3.2/4.6 GHz to cover PCS1900, WiMAX, and C-band applications. A three-pole Chebyshev parallel-coupled microstrip bandpass filter was designed at a center frequency of 3.2 GHz and used as the basis to validate the gapping effect on the filter respo...

A flexible approach for designing dual-mode dual-band bandpass filters with controllable passband frequencies is presented. Two dual-mode dual-band bandpass filters are proposed for experimental verification. The first filter, whose two passbands are centered at 3.4 and 5.5 GHz with the corresponding fractional bandwidth of 19 and 13%, respectively, is suitable for the applications of worldwide interoperability for microwave access (WiMAX) and wireless local area network. The second filter, whose two passbands are centered at 4 and 7.4 GHz with the corresponding fractional bandwidth of 25 and 13%, respectively, is suitable for the downlink of C-band and X-band satellite communication systems. Both filters have been designed, fabricated, and measured. The measured results show good agreements with those of the simulation.

In this work, a planar microstrip tri-band filter based on quarter-wavelength resonators is presented, which allows independent control of the positions of all three passbands. Furthermore, the topology of the filter provides five transmission zeros and thus results in a highly selective response in all passbands. A synthesis procedure of the filter is presented and used to design a tri-band filter which operates at WLAN frequencies of 2.4/3.5/5.2 GHz. The designed filter outperforms all other state-of-the-art tri-band filters in terms of compact size, high selectivity and transmission, and return-loss characteristics.

In this paper, a dual-band bandpass filter based on half-wavelength resonator is realized by adding shunt stubs. The added stubs are separately located on either side of the resonators to generate a second passband. To demonstrate the idea, transmission zeros and ABCD matrix of the filter are investigated. The filter is centered on 2.4 and 3.95 GHz with bandwidths 260 and 150 MHz, respectively. Furthermore, a novel bandpass filter based on half-wavelength resonator is designed to suppress harmonics. Rectangular grooves and perturbation stub are used to suppress the harmonics and improve the performance of the filter. Advantages of small size and low insertion loss can be obtained. At last, agreement between simulated and measured results validates the design theory.

We propose a novel bandpass filter miniaturized by the composite right- and left-handed (CRLH) zeroth order resonators (ZORs) which form a cascaded triplet (CT) to have a significantly sharp skirt for high frequency selectivity. A 3rd-order UHF bandpass case is tested. Therefore, firstly, we design an in-line ZOR bandpass filter whose total size is nearly 0.3 times the size of the paralleledge coupled filter. Secondly, we create a transmission zero (TZ) by changing the three in-line ZORs of the filter to a CT. As a result, with the insertion loss less than 1.1 dB and return loss less than −15 dB, the proposed filter has the size-reduction so that its size is smaller than 1/3 of a 3rd-order parallel-edge coupled filter, and its skirt is as steep as a 6th-order Chebyshev filter. The simulation and measurement validate the proposed design method, and the CRLH ZOR properties are proven by the no-phase variation electric field and dispersion diagram.

In this paper, a compact microstrip bandpass filter is presented by using a proposed improved hybrid resonator. Without requiring the cross-coupling and the source-load coupling, the new filter has a transmission zero on the upper stopband to provide a high selectivity. The fabricated filter is designed at f 0 = 1 GHz and has a compact size of 0.112λg×0.057λg. Good agreement is observed between the measurements and simulations. The measured results show that the new filter has a wide −60 dB rejection upper stopband from 1.24f 0 to 4.05f 0. In addition, a −20 dB rejection ultra-wide upper stopband is measured from 1.08f 0 to 15.38f 0. The new filter can be fabricated using the standard printed-circuit-board (PCB) process and has a planar topology, which is easily integrated with the modern wireless communication system.

This paper presents the design and implementation of a 60-/110-GHz millimeter-wave CMOS dual-band on-chip bandpass filter. This miniaturized dual-band filter using embedded metamaterial resonators (EMRs) and half wavelength open-loop resonators has been proposed. The EMRs are designed to have both left and right hand modes, which are simultaneously excited by the composite right/lefthanded (CRLH) structure. The half wavelength open-loop resonator is designed to provide another passband. Without using an external dual-band impedance transformer, the proposed structure can provide two transmission passbands. The dual-feed structure is presented to control the external quality factors of the first and second bands. Such an approach leads to a significant reduction for the on-chip area. Also, the frequency selectivity and impedance matching are further improved. Finally, this designed bandpass filter with the core size of 0.351 mm × 0.245 mm has been fabricated on a 0.18-μm standard CMOS process. The insertio...

This paper presents a tri-band bandpass filter in which a dual-band bandpass filter (BPF) and a single-band bandstop filter (BSF) are integrated into a single circuit of short length. The dual-band BPF contains several two-section stepped-impedance stubs which are mounted onto a main transmission line. The BSFs are constructed using capacitor-loaded shunt stubs which are connected by transmission lines. After circuit embedding, one wide passband of the dual-band BPF is converted into two passbands by the stopband of the BSF, resulting in a total of three passbands. A prototype tri-band filter is designed according to prescribed specifications: the required passbands are 1–1.4, 1.8–2.0 and 2.42–2.66 GHz with return loss above 10 dB, while the expected isolations between bands are above 40 dB. Optimization method is adopted for extracting the circuit parameters. The simulated and measured results are compared, and good features such as low insertion loss and high isolation are demonstrated.

A novel tunable bandpass filter with constant absolute bandwidth is presented in this paper. Introducing a mixed electric and magnetic coupling structure and a new external coupling scheme, nearly constant absolute bandwidth is maintained across the tuning range. Theoretical analysis and design approach are demonstrated. The proposed filter is designed with a frequency coverage of 0.78–1.08 GHz and constant 3-dB bandwidth of 50 MHz over the tuning range. The experimental results show good performance of the filter and validate the design concept.

A triple-band bandpass filter based on tri-section step impedance resonator (SIR) is proposed to realize compact size with low return loss and wideband characteristic. The center frequencies of the proposed filter are 1.9/5.65/9.2 GHz, which can be used in wireless communication system. The absolute bandwidth of this triple-band bandpass filter is almost 1 GHz with 53% fractional bandwidth at −3 dB, and it has been shown that the performance of the second and the third frequency is improved greatly by two high impedances. For demonstration, the filter has been fabricated and the experimental results show the excellent agreements with theoretical simulation results.

A novel three-line microstrip structure wideband bandpass filter is presented. Diamond structures of input/output ports are employed as matching circuits. Compared with the traditional three-line filter, the proposed three-line filter not only retains virtues of the traditional three-line filter, but also resolves drawbacks of it, which include discontinuities between adjacent sections, number of design parameters, and no effective matching circuits at input/output ports. To validate the proposed three-line filter, an eleven-pole millimeter-wave wideband bandpass filter is designed and fabricated. Good agreement between simulated and measured responses is observed.

This paper presents a novel approach for designing planar triple-mode bandpass filters with good selectivity. The proposed triple-mode resonator is developed from traditional dual-mode stub-loaded resonator, and it is composed of a section of half-wavelength (λ/2) open-ended microstrip line and a pair of open-ended stubs. The field patterns of the three modes associated with theoretical analysis are investigated. By modifying the proposed triple-mode filter, a compact triple-mode bandpass with several transmission zeros in stopband is realized. The controllable transmission zeros provide a good selectivity to the filter. An experimental filter is fabricated, and both the simulated and measured results are presented.

A novel dual-mode dual-band bandpass filter (BPF), which is fabricated with a 0.5-μm pHEMT MMIC technology is presented. A design method that can precisely determine optimal elements' values of a wide-band dual-mode filter based on desired passband specifications is developed. This filter is constructed using two stacked ring resonators with individual perturbations and feeding capacitors, so both fractional bandwidths and center frequencies of the dual-band filter can be flexibly controlled. Benefiting from the multilayer capability of the advanced process, the feeding structure connecting the two stacked ring resonators can be easily implemented using a compact metal-insulator-metal (MIM) structure rather than a large-sized coupling scheme. The size of the filter is only 0.47×0.8 mm2, and the measured insertion losses in lower and upper pasbands are less than 2.4 dB and 3.0 dB, respectively. The associated return losses in the passbands are all greater than 15 dB.

A compact double-layered quad-band (DLQB) bandpass filter (BPF) is presented to provide four passbands at the desired frequencies with efficient out-of-band suppression. The designed filter is verified by pattern implementation on two FR4 boards. The proposed DLQB-BPF consists of two L-shaped resonators on the first layer and two symmetrically-coupled stepped-impedance resonators (SIRs) on the second layer. The bottom of the second layer is ground plane. There are seven transmission zeros generated to perform quad-band characteristics at 1.57 GHz, 2.45 GHz, 3.6 GHz, and 5.8 GHz. An equivalent circuit model is constructed by analyzing the symmetry property of the proposed filter. A good agreement between the simulated and measured results is observed.

A new technique is presented for the derivation of the quasi-elliptic function. Based on maximizing the band-edge selectivity (BES) of elliptic filters without increasing filter order, the equal ripple parameter of quasi-elliptic function can be obtained when the BES of the elliptic function and quasi-elliptic function are the same. The exact quasi-elliptic function not only keeps the bandwidth invariable, but effectively improves the selectivity. Finally, a novel quasi-elliptic microstrip filter composed of four spiral stepped-impedance resonators (SIR) is designed. The simulated and measured results show that the filter has not only smaller size, but also a wider upper stopband.

In this paper, a new approach to design multiple-band microwave filters is presented. A transfer function of a cascade of a low pass prototype filter with one or more band reject filters is calculated. This transfer function is manipulated to make its application to a single coupled-resonator filter. This method can be applied to design symmetric and asymmetric multiple-band filters.

This paper presents a novel harmonic-suppressed microstrip open-loop resonator bandpass filter with the different transmission line characteristic impedance of the feed line and open-loop resonator for wireless local area network (WLAN) application. To improve the stopband rejection of the filter, the dumbbell-shape defected ground structure (DGS) are applied under the feed lines to suppress the harmonics and the equivalent parameters extraction formulations of double-dumbell-shaped DGSs are the first to proposed. The bandpass filter with center frequency of 2.44 GHz were designed and fabricated on a TLX substrate with thickness of 1 mm and dielectric constant of 2.55. Measurement results show the filter has a wide stopband characteristic with 30 dB attenuation up to 7.5 GHz and only has an –1.23 dB insertion loss while it is a little larger than the conventional one. The measured results are in good agreement with the simulated results. It can be widely used for WLAN application.

A miniaturized dual-mode bandpass filter with controllable harmonic response for dual-band applications is presented in this paper. The new bandpass filter is designed with loading distributed capacitors in the inner area of conventional dual-mode loop resonator. This loading can realize both compact size and controllable harmonic response of the filter. A demonstrated filter with the dual-band operating at 1.8 and 2.6 GHz was designed, fabricated and measured. Simulated and measured results indicate that a high selective dual-mode dual-band filter with its size reduced to 34.5% of the conventional case at about 1.8 GHz has been achieved.

This paper presents an improved bandpass filter based on Stepped-Impedance Resonator (SIR) working in millimeter-wave band. Compared to the conventional E-plane waveguide bandpass filter, it can be integrated in the planar circuits easily with more compact size. A new coupling structure is proposed which has increased the coupling coefficient of the 1st and 5th stages at the limitation of fabricating craft in millimeter-wave band. The distorted structure of the microstrip reduces the insertion loss of the filter. The relative analysis is given, and the simulation results are compared with those of traditional structure. Computer-aided design of such a Ka-band filter has been presented. Good agreement has been observed between theory and measurement.

A novel dual-mode dual-band bandpass filter using meander-loop resonators is proposed in this letter. Different meander-loop resonators are operated for respective passbands. Several finite attenuation poles in stopbands are realized to improve the selectivity of the proposed bandpass filter and isolation between the two passbands. Compact size, dual band and high selectivity characteristics are realized by this type of filter structure. The filter is evaluated by experiment and simulation with very good agreement.

A novel dual-mode bandpass filter based on conventional triangular structure is designed in this paper. The filter has the characteristics of compact structure, low insertion loss and so on. Several attenuation poles in the stopband are realized to improve the selectivity of the proposed bandpass filter. The experimented results were in good agreement with simulated results.

A microstrip bandpass filter implemented with slow-wave open-loop resonators is described in this letter. The slow-wave open-loop resonators make the filter compact and allow implementation of positive and negative inter-resonator couplings. Implementation of the positive and negative couplings is used to introduce a pair of finite frequency transmission-zeros in the filter response. The two zeros are designed to be close to the passband, thus improving the selectivity of the filter. As an example, a quasi-elliptic filter is fabricated. The quasi-elliptic filter has a compact dimension of 22.1 mm × 21.16 mm, which is approximately 0.1705λg × 0.1634λ g . The experimental results are demonstrated and discussed.

This paper presents a novel harmonic-suppressed microstrip open loop resonator bandpass filter with defected ground structure (DGS) for wireless local area network (WLAN) application. To improve the stopband rejection of the filter, DGSs are applied under the feed lines to suppress the harmonics. The bandpass filter with center frequency of 2.44 GHz is designed and fabricated on a TLX substrate with thickness of 1 mm and dielectric constant of 2.55. By using two dumbbell-shape DGSs the filter has a wide stopband characteristic with attenuation −25 dB up to 8 GHz and has an −1.25 dB insertion loss while it demonstrates a little larger than the conventional one. The measured results agree well with the simulation results. The proposed filter is found to possess low in-band insertion loss and high out-band suppression, making it suitable in WLAN application.

Dual-mode and multi mode techniques have very important applications for microwave filter design to implement miniaturization and nicer performances of transmission zeros, wide band and so on. This paper presents a new multi mode bandpass filter with wide passband and two kinds of new DC-block dual-mode bandpass filters by using an isosceles right-angled triangular resonator which with much less attention, all have transmission zeros and low passband insertion losses. The new filters have novel, compact and simple structures as well as nicer performances, and are quite useful for modern RF/microwave circuits and systems.

This paper presents a novel dual-band banpass filter using microstrip open-loop resonators. A new microstrip unit of dual-band bandpass filter is introduced, which can be used as unit element of duan-band filter design. The two open-loop resonators are treated as passband resonator and stopband resonator in analysis, respectively. A five-pole C-band dual-band bandpsss filter has been designed and fabricated. The measured results show a good agreement with the simulated results.

A novel design method of dual-band and tri-band band-pass filters is proposed in this paper. A compact loaded open-loop resonator(LOLR) structure is introduced. The resonant frequency response of the resonator is described in detail. A dual-band filter and a tri-band filter are designed with the LOLRs. 0° feed structures are applied to improve the selectivity of the proposed filters. The measurements of the filters are in good agreement with the simulated results.

A novel design method has been developed for E-plane bandpass filter synthesis based on an electromagnetic artificial neural network (EM-ANN) model. EM-software analysis is employed to characterize an E-plane strip. The EM-ANN model is then designed by exchanging the EM-software input/output. The filter is designed without finding the physical parameters by solving equation. A W-band E-plane bandpass filter is designed by this method, the insertion loss of which is less than 1.5 dB, and the center frequency is 94 GHz with a bandwidth of 4 GHz.

Three types of novel microstrip bandpass filters, a square split ring stepped-impedance bandpass filter, a square ring stepped-impedance bandpass filter, and a dual-mode square ring bandpass filter, which operate from L to S waveband are proposed, their filter performances are calculated. In these novel structures, ring stepped-impedance resonator, DGS and dual-mode technique are applied to not only reduce the volume but also improve the frequency responses of filters. The optimized results show that microstrip bandpass filter with DGS has nicer performances such as low insertion losses, wide stopband responses etc., while with dual-mode technique, a pair of transmission zeros can be implemented and the filter performances are effectively improved. The filters proposed in this paper have outstanding advantages such as compact and novel structures, small volumes, high selectivity, wide stopband responses, low insertion losses and so on, and can be applied in wearable systems.

Length reduction of evanescent-mode ridge waveguide bandpass filters is investigated extensively. Based on the conventional filter configuration, two new filter configurations are proposed: one is the generalized filter, and the other is the folded filter. In the generalized filter configuration, the cross sections of the evanescent waveguide and the ridge waveguide are not necessarily the same. It is found that the filter length can be reduced by enlarging the evanescent waveguide height. In the folded filter configuration, the filter is folded back at the middle coupling section. The folded junction is ridged to provide the required coupling between the two ridge waveguide resonators it connects. A design example demonstrates the feasibility of this filter configuration.