Dual-band Bandpass Fllter Research Articles

AN INDEPENDENTLY TUNABLE DUAL-BAND FILTER USING ASYMMETRIC λ/4 RESONATOR PAIRS WITH SHARED VIA-HOLE GROUND

This paper presents a dual-band tunable bandpass fllter with independently controllable dual passbands based on a novel asymmetric ‚=4 resonator pair with shared via-hole ground. Because two separated passbands can be independently generated by the two ‚=4 resonators with difierent electric lengths, the asymmetric ‚=4 resonator pair can realize ∞exible passband allocation when it is utilized to design dual-band fllters. Two varactors are placed at the two open circuit ends of the asymmetric ‚=4 resonator pair to control the two dominant resonant frequencies, respectively. A prototype tunable dual-band fllter with Chebyshev response is designed and fabricated. The measured results are in good agreement with the full-wave simulated ones. The results show that the flrst passband varies in a frequency range from 0.88GHz to 1.12GHz with the 3-dB fractional bandwidth of 5.1%{6.4%, while the second passband can be tuned from 1.5GHz to 1.81GHz with the 3-dB fractional bandwidth of 5.4%{6.4%.

DESIGN OF A MINIATURIZED DUAL-BAND BANDPASS FILTER WITH HIGH SELECTIVITY

In this paper, a miniaturized dual-band bandpass fllter with high selectivity and band-to- band isolation is presented. The fllter consists of two quarter-wavelength stepped impedance resonators (SIRs) which share a common grounded via-hole and two symmetrical half-wavelength SIRs which are embedded into the inner space to reduce the size of the fllter. Two independent mixed coupling paths which are created by the coupling between these SIRs introduce two difierent passbands. Five transmission zeros (TZs) are generated near the two passbands to achieve high frequency selectivity and band-to-band isolation. To validate the design theory, a dual-band fllter operating at 2.45 and 5.2GHz was designed and fabricated. The size of the proposed fllter only occupies 0:095‚g £ 0:109‚g and the measured 3dB fractional bandwidth (FBW) of the flrst and second passbands is 11.5% and 7.4% respectively. The measured results are in good agreement with the simulated results.

A FOLDED SIR CROSS COUPLED WLAN DUAL-BAND FILTER

A compact cross-coupled dual-band bandpass fllter based on folded Stepped Impedance Resonators (SIRs) with four controllable transmission zeros is proposed in this paper. A pair of stepped impedance tapped lines is utilized to improve the dual band impedance matching, which reduces the insertion loss of the fllter; meanwhile the tapped lines are also coupled with non-adjacent resonators to produce transmission zeros to improve skirt characteristics. At the end of this paper, the simulated and measured results are compared with each other, and good agreement is achieved.

DESIGN OF DUAL BAND FILTER BASED ON A NOVEL DGS STRUCTURE

This letter presents a dual-band bandpass fllter (BPF) using interdigital coupling lines with a new defected ground structure (DGS) pattern. Traditional DGS structures are mainly used to realize wide bandstop characteristics. In this letter, by introducing a pair of coupling stubs in the aperture of the DGS, a narrow passband can be achieved within a wide stopband, so a dual-band bandpass fllter can be implemented. An equivalent circuit model is derived to describe the fllter. And the circuit simulation result agrees well with the EM simulation one. The position and bandwidth of the two passbands can be designed and adjusted independently. In order to verify the theory, a dual-band bandpass fllter is designed, fabricated and measured. The simulated and measured results are in good agreement.

DUAL-BAND DIFFERENTIAL FILTER USING BROADBAND COMMON-MODE REJECTION ARTIFICIAL TRANSMISSION LINE

A new balanced dual-band bandpass fllter with strong common-mode rejection is presented in this paper. Common-mode rejection is provided by a section of a periodic microstrip difierential line that behaves as a low-pass fllter under common-mode operation. In contrast, the difierential line exhibits very good all-pass behavior under difierential mode operation. This structure is combined with a difierential dual-band bandpass fllter based on embedded resonators. Simulations and experiments conflrm that the combined structure has good common-mode rejection within the passbands of the dual-band difierential fllter.

A COMPACT DUAL-BAND BAND-PASS FILTER WITH WIDE STOP-BAND USING TWO RESONATORS COMBINED BY VIA-HOLE

A compact dual-band band-pass fllter is proposed in this paper. The central frequencies of the passbands are around 2.46GHz and 5.86GHz. There are two resonators located at the top side layer and the bottom side (the CPW) layer, respectively. Dual-resonance operation usually needs two resonators on the same layer to generate two passbands simultaneously. However, in this paper the size can be reduced e-ciently by connecting resonators at two layers through via-holes to implement dual-band performance. Furthermore, the stop- band for this novel fllter with T slot-line, L-line and rectangular micro- strips can be extended to 30GHz. To verify the feasibility of the design above, a dual-band band-pass fllter has been implemented on a Rogers RT5880 substrate (thickness is 0.508mm). This fllter with passbands operated at 2.46GHz and 5.86GHz can flnely meet the IEEE 802.11n wireless local area network (WLAN) bands requirements.

A NOVEL DUAL-BAND PASSBAND FILTER WITH CONTROLLABLE CENTER FREQUENCIES AND BANDWIDTHS

A high-order dual-band bandpass fllter using novel combined stub-loaded resonators (CSLRs) is presented in this paper. The key merits of the fllter conflguration are that the center frequency and also the bandwidth of each passband can be controlled conveniently. Moreover, it can build the high-order dual-band bandpass fllters using the proposed resonators because of the su-cient coupling through the four symmetric stubs. A flfth-order dual-band bandpass fllter designed at 2.5/3.5GHz was built and tested. The measurement and simulation results agree very well, demonstrating the validity of the method.

A DUAL-BAND BANDPASS FILTER WITH A TUNABLE PASSBAND

In this paper, a novel dual-band bandpass fllter with a tunable passband is proposed. Based on two quarter-wavelength resonators and one half-wavelength resonator, dual-band character is designed by introducing two independent coupling paths. The fllter structure is designed and can be divided into two parts. The Transmission Zeros (TZs) are derived through simulation. By varying the reverse bias voltage applied to the varactor diodes which are connected to the resonators, the flrst passband can be independently tuned. The second passband can be easily controlled by the width of the half-resonator. Finally, simulation results show a flrst tunable passband with a constant fractional-bandwidth of 3:9 § 0:3%, a center frequency of 1.472{1.886GHz, and the second passband almost remains constant with a fractional-bandwidth 2.4% at frequency range 2.24GHz. The measurement of the fabricated example shows good agreement with the simulation.

DUAL-MODE DUAL-BAND BANDPASS FILTER BASED ON SQUARE LOOP RESONATOR

In this paper, a dual-mode dual-band microstrip bandpass fllter utilizing asymmetric square loop resonators is proposed. A pair of bent open-circuited stubs is installed to the loop as perturbation stubs. By stretching the perturbation stubs more than half-wavelength of the loop, the degenerated modes in a loop are split for dual-band operation. Two asymmetric resonators are cascaded to form two bands. Even- and odd-mode analysis method is used to deduce the resonant frequencies of two bands. Based on the transmission line theory, resonant frequencies of the two resonances are derived. According to the resonant conditions, a kind of dual-mode dual-band bandpass fllter can be easily designed. Finally, a dual-band fllter with two bands centering at 1.9GHz and 2.6GHz is designed in a comprehensive way. Measured results of experimental circuit show good agreement with simulated responses.

DUAL-BAND BANDPASS FILTER USING A SINGLE SHORT-ENDED DUAL-MODE RESONATOR WITH ADJUSTABLE FIRST PASSBAND

In this paper, a novel dual-band bandpass fllter (BPF) based on a single short-ended dual-mode resonator (SEDMR) is presented. According to the voltage distribution of the resonator, two pairs of loaded open stubs, inside and outside of the resonator, are utilized to tune the center frequency and the external quality factor of the flrst passband respectively, while there is no in∞uence on the second passband. Meanwhile, source-load coupling is introduced to produce transmission zeros to improve the passband selectivity and band-to-band isolation. For demonstration, a dual-band fllter working at 1.52GHz for GPS and 3.5GHz for WiMax is designed, fabricated and measured with insertion losses of 1.47 and 0.95dB. In addition, two transmission zeros, introduced by source-load coupling, located at 2.19 and 2.67GHz between the flrst and second passband improve passband selectivity and band-to-band isolation better than 50dB.

A NOVEL QUAD-MODE RESONATOR AND ITS APPLICATION TO DUAL-BAND BANDPASS FILTERS

In this paper, a novel square-loop quad-mode resonator is presented. Due to its symmetry, the even-odd-mode method is utilized to analyze the resonant characteristics. Two modes resonating at lower frequencies are employed to construct the flrst passband, and other two form the second passband. Meanwhile, both passband center frequencies can be controlled by the corresponding physical dimensions. Two dual-band bandpass fllters (BPFs) without and with source-load coupling operating at 2.4 and 3.5GHz are designed based on the proposed quad-mode resonator. Due to the source-load coupling, the passband selectivity and band-to-band isolation of the latter one are better than those of the former one. For demonstration, these two fllters are fabricated and measured, and the measured results show good agreement with the simulated ones.

AN APPROACH FOR MULTI-BAND BANDPASS FILTER DESIGN BASED ON ASYMMETRIC HALF-WAVELENGTH RESONATORS

This paper presents that the extra passband with two transmission zeros can be obtained by adding shunt open stubs to the asymmetric half-wavelength resonators structure. By using this method, a fourth or even higher passband with good selectivity and compact size can be obtained. Dual-band, tri-band and quad-band bandpass fllters are demonstrated by using this method. The measured bandwidth is 80/180MHz for the dual-band, 60/180/180MHz for the tri-band and 130/360/170/70MHz for the quad-band fllter, respectively. The measured insertion loss for the dual-band, tri-band and quad-band fllter is less than 2.7dB, 2.5dB and 2.9dB at the center frequency. All the simulated results and the measured results agree well.

CO-DESIGN OF A COMPACT DUAL-BAND FILTER-ANTENNA FOR WLAN APPLICATION

A co-designed compact dual-band fllter-antenna suitable to be embedded inside a wireless access point (AP) in the 2.45/5.2- GHz wireless local area network (WLAN) bands is presented. The proposed fllter-antenna comprises a loop-loaded dual-band monopole radiator and a microstrip dual-band pseudo-interdigital bandpass fllter. The monopole consists of a uniform width monopole, two identical capacitively loaded magnetic resonators and a top loaded loop. The two magnetic resonators are loaded at the center of the monopole for dual-band operation and the rectangular loop loaded at the top is involved for miniaturization. Instead of using the traditional 50› interfaces, the impedance between the fllter and antenna is optimized to improve the performance. The fllter-antenna and the system circuit board of an AP share the same substrate and ground plane. In this case, the design can fully integrate the circuit board of the AP into an internal fllter-antenna solution. The proposed fllter-antenna provides good selectivity and rejection in out of band regions and omni-directional radiation patterns within the two desired bands. The measured results show good agreement with the simulated ones.

A HIGH SELECTIVITY DUAL-BAND BANDPASS FILTER USING DUAL-MODE AND TRIPLE-MODE RESONATORS

In this paper, a novel high selectivity dual-band microwave bandpass fllter (BPF) using dual-mode and triple-mode resonator is proposed. First, a dual-band fllter comprising two dual-mode single band fllters using common input/out lines is designed. Each single BPF is realized using a stepped-impedance resonator (SIR) with a centrally-loaded shunt open stub. The flrst and second passband can be independently controlled by the two dual-mode resonators, respectively. The proposed fllter also ofiers three transmission zeros (TZs) to improve the selectivity. To further improve the selectivity over high side band of the flrst passband, a novel triple-mode resonator is designed to replace the dual-mode resonator. The basic structure of triple-mode resonator is microstrip-to-coplanar waveguide (CPW) structure. The microstrip structure provides one odd mode and one even mode resonant frequency and the CPW structure can provide another even mode resonant frequency without increasing circuit size. Both simulated and measured results show that the fllters exhibit a good performance, including a small insertion loss, selectivity.

COMPACT MICROSTRIP DUAL-MODE DUAL-BAND BANDPASS FILTERS USING STUBS LOADED COUPLED LINE

This paper presents two novel dual-mode dual-band bandpass fllters (BPFs) by using stubs loaded coupled line. The analytical equations of their transmission poles and transmission zeros are given by the classical even-/odd-mode method. Design rules for two dual-band BPFs are also given, which show the easily tuned passband frequency locations and in-band performance. As examples, two dual- mode dual-band BPFs, dual-band fllter A with central frequencies (CFs) at 3.5/6.8GHz and i3dB fractional bandwidth (FBW) of 14%/10%, while dual-band fllter B with CFs at 2.4/6.8GHz and i3dB FBW of 43%/16% are designed, fabricated and measured. Good agreement can be observed between the simulations and measurements. These two fllters exhibit simple design procedures, simple physical topology, low insertion losses, good return losses, high isolation and compact sizes.

INDEPENDENTLY-TUNED DUAL-BAND FILTER USING VARACTOR-LOADED RESONATORS

This paper presents a high-selectivity dual-band bandpass fllter with independently-tunable passband frequencies. A tap-coupled structure is utilized to feed the two resonators at lower passband and a coupling structure is used to feed the two resonators at the upper passband. Two pairs of varactor-loaded resonators operating within two difierent frequency ranges, allow the independent passband frequency tuning. Using this conflguration, it is convenient to tune the center frequency of each passband, while the responses of the other passband remain unaltered. Source-load coupling is realized to generate transmission zeros, resulting in high skirt-selectivity. The transmission zeros move synchronously with the passbands, ensuring sharp roll-ofi rate for all tuning states. To verify the proposed idea, a demonstration microstrip tunable bandpass fllter is implemented. The simulated and measured results are presented.

DESIGN OF A MINIATURIZED DUAL-BAND DOUBLE-FOLDED SUBSTRATE INTEGRATED WAVEGUIDE BANDPASS FILTER WITH CONTROLLABLE BANDWIDTHS

One miniaturized multilayer dual-band bandpass fllter (BPF) is developed using standard low temperature co-flred ceramic (LTCC) technology. The fllter makes use of four double-folded substrate integrated waveguide (SIW) resonators. Two sets of coupling paths between the source and load are implemented to generate dual- band responses. Utilizing this method, the two passbands can operate at independent frequencies and the bandwidth can be easily controlled. High isolation is obtained between two passbands, and two pairs of transmission zeros close to the passband edges are generated by source- load coupling, resulting in high skirt-selectivity. Good agreement between the simulated and measured results of the fllter sample is obtained, with its high electrical performance validated.

DESIGN DUAL-MODE BANDPASS FILTERS BASED ON SYMMETRICAL T-SHAPED STUB-LOADED STEPPED-IMPEDANCE RESONATORS WITH HIGH FREQUENCIES SELECTIVITY

A novel approach for designing planar dual-mode bandpass fllters using symmetrical T-shaped stub-loaded stepped- impedance resonators (TSLSIRs) with high frequencies selectivity is presented. The proposed symmetrical TSLSIR structure is mainly composed of three elements, i.e., a stepped-impedance resonator (SIR), and two T-shaped stubs which symmetrically loaded at the middle sections of the SIR. Two dual-mode bandpass fllters based on TSLSIRs with high frequency selectivity are proposed for experimental veriflcation. Firstly, a dual-mode single passband fllter with two transmission zeros located at the both sides of passband is presented, whose passband is centered at 5.23GHz with the fractional bandwidth of 10.1%, and a wide upper-stopband with harmonic suppression better than 20dB in the range of 5.9GHz to 12.9GHz is achieved. Secondly, a dual-mode dual-band bandpass fllter with four transmission zeros located at the both sides of the two passbands is presented, whose two passbands are centered at 3.4GHz and 4.54GHz with the corresponding fractional bandwidth of 8.4% and 7.5% respectively, and the spurious frequencies from 4.9GHz to 8.45GHz are successfully suppressed to the level of lower than i20dB. Both fllters have been designed, fabricated and measured. The measured results show good agreements with those of the simulation.

TWO KINDS OF DUAL-BAND BANDPASS FILTER BASED ON A SINGLE SQUARE RING RESONATOR

In this paper, two kinds of dual-band bandpass fllter (BPF) based on a single square ring resonator are presented, which are realized by loading capacitance or inductive stubs, respectively. Even- odd-mode analysis is applied to explain their model characteristics. One fllter is implemented by loading a pair of capacitance stubs, and both in-band couplings can be tuned in a reasonable range. Another fllter is completed by loading a pair of inductive stubs, and the flrst and second passband center frequencies can be controlled independently. For demonstration, two fllters operating at 2.45/5.25GHz and 2.4/5.25GHz are designed and fabricated. The simulated and measured results show good agreements.

A COMPACT TUNABLE DUAL-BAND BANDPASS FILTER BASED ON SUBSTRATE INTEGRATED WAVEGUIDE AND DEFECTED GROUND STRUCTURE

A compact tunable dual-band bandpass fllter (BPF) based on substrate integrated waveguide (SIW) and defected ground structure (DGS) is investigated in this paper. The second passband can be ∞exibly controlled by changing the dimensions of the up- down DGSs whereas the flrst passband is flxed. The proposed fllter exhibits improved selectivity due to the introduction of four left-right DGSs generating transmission zeroes. To verify the design method, a compact dual-band fllter with the second center frequency switched among 5.4GHz, 5.8GHz, 6.4GHz and 6.8GHz and the flrst center frequency flxed at 4.78GHz, is designed and fabricated. The simulated and measured results are in good agreement with each other.