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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 f0 = 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 1.24f0 to 4.05f0. In addition, a -20 dB rejection ultra-wide upper stopband is measured from 1.08f0 to 15.38f0. 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. [ABSTRACT FROM AUTHOR]

This paper presents a new balanced dual-band bandpass filter (BPF) designed for 2.4/5.2 GHz wireless local area networks (WLANs). Because adopted in the BPF are only bi-section equal-electric-length stepped-impedance resonators (SIRs), whose dimensions can be determined using analytic formulas, the BPF can be easily and efficiently designed. The inner SIRs are designed to resonate only at the odd-mode resonant frequencies of the input and output SIRs but not at the even-mode ones. This leads to well-behaved differential-mode (DM) transmission and excellent common-mode (CM) suppression for the BPF. Simulated and measured results are found to agree quite well to each other. The measured minimum DM insertion losses in the two passbands are 2.1 and 2.54 dB, whereas the measured CM rejections are higher than 33 dB in the frequency range from 1 to 7 GHz. [ABSTRACT FROM AUTHOR]

In this paper, we have proposed the design of novel compact dual-band bandpass filter (BPF) with high band selectivity by using only two asymmetric stepped impedance resonators (SIRs) with one step discontinuity. By arranging the cross-coupled SIRs, three transmission zeros near the passband edges and a high isolation between two passbands are introduced to improve the band selectivity of the proposed filter. The dual-band frequencies of this BPF is implemented by properly selecting the impedance ratio (R) and physical length ratio of the asymmetric SIRs. The bandwidths and the coupling coefficients of the two passbands (2.4/5.2 GHz) can be designed by adjusting the coupling gap between the resonators. The proposed BPF has a smaller circuit size in comparison with previous works using conventional direct-coupling SIRs. The measured results are in good agreement with the full-wave simulation ones. [ABSTRACT FROM AUTHOR]

A novel dual-band filter using open loop ring resonator (OLRR) and defected stepped impedance resonator (DSIR) is presented in this paper. The OLRR forms one pass on the upper plane, and the DSIR forms the other pass on the lower plane. A proper designed feed structure is analyzed and used, which can provide desired external couplings to the two passes independently. At last, a dual-band filter with cascaded quadruplet (CQ) topology is designed and fabricated, which operates at WLAN bands 2.45/5.25 GHz. The simulated and measured results show good agreements and validate the proposed design method. [ABSTRACT FROM AUTHOR]

This paper presents a second-order dual-band balanced bandpass filter (BPF) designed using bi-section quarter-wavelength (λ/4) stepped-impedance resonators (SIRs) and folded feed lines. The first two modes of the λ/4 SIRs are designed to resonate in the designated 2.4- and 5.2-GHz WLAN bands. High-impedance folded transmission-line sections are inserted in series with the feed lines to improve the overall impedance matching at the input/output ports, so that the signal transmission can be enhanced. In addition, the feed lines and λ/4 SIRs are properly arranged to form an all-stop-like coupling configuration for common-mode operation. For the first (second) operating band of interest, the fabricated balanced BPF printed on an FR4 substrate was measured to have a minimum differential-mode insertion loss of 3.03 dB (4.3 dB) and a minimum common-mode rejection level of as high as 15.7 dB (22.3 dB). [ABSTRACT FROM AUTHOR]

In this paper, a new band-notched UWB BPF with a very wide upper stopband is designed using a λ/4-type multi-mode resonator (MMR). The proposed MMR, being formed by combining two identical λ/4 tri-section stepped-impedance resonators (TSSIRs) in a structure-shared fashion, exhibits both λ/4 and embedded λ/2 types of resonance with a relatively smaller circuit size. By properly locating the first four resonant modes of the MMR and the coupling peaks of the input/output parallel-coupled lines, a five-transmission-pole UWB BPF is realized with a favorable uniform in-band UWB response. Besides the good UWB performance, a 5-GHz notched band is created by embedding in the output feed line a T-shape lumped-element bandstop structure to reject the influence from WLAN signals. Also, a very wide upper stopband is achieved by implementing a compact bandstop filter structure in the input feed line together with the properly located transmission zeros generated by the input/output interdigital-coupled lines and the second harmonic of the T-shape bandstop structure. A prototype of the proposed UWB BPF was fabricated and measured for performance verification. The measured results show a return loss of higher than 10 dB, a minimum insertion loss of 0.41 dB, and a group delay variation of less than 0.11 ns in the UWB passband except the notch. The notched band has a 3-dB bandwidth of 18%. The measured upper-end –20-dB stopband ranges from 11.94 to 30.56 GHz, with a bandwidth of 18.62 GHz. [ABSTRACT FROM AUTHOR]

A new band-notched ultra-wideband (UWB) bandpass filter (BPF) with an improved upper stopband is designed using a multi-mode resonator (MMR). The MMR, being a modified version of a common tri-section stepped-impedance resonator (TSSIR), is split at its two open ends with the input/output feed lines sandwiched in between to form an interdigital parallel-coupled configuration that results in stronger coupling. In addition, an extended coupling length in the second section of the TSSIR is featured to provide further coupling and impedance-matching tuning. With such a design strategy, coupling gaps of no smaller than 0.1 mm was achieved to obtain the required UWB response. In this design, the first five resonant modes of the MMR and the coupling peaks of the input/output parallel-coupled lines are properly located in the UWB passband to achieve a uniform in-band transmission response. Also, the spur lines and open-circuited stubs are implemented in the MMR to create a 5-GHz notched band and to broaden the upper stopband, respectively. The designed UWB BPF, which being verified by measurement, shows a very good UWB performance. The measured in-band minimum insertion loss and maximum group delay variation except those in the notched band are 0.45 dB and 0.05 ns, respectively, and the upper-end -20-dB stopband bandwidth is about 5.35 GHz. The created notched band is centered at 5.69 GHz with a maximum insertion loss of 37.2 dB and a 3-dB notch bandwidth of 18%. [ABSTRACT FROM AUTHOR]

A wideband cross coupled bandpass filter making use of square split-ring resonator (SRR) defected ground structure (DGS) and parallel microstrip feed line is presented in this paper. The coupling between a pair of SRR DGS is much larger than that of the conventional SRR, which is fully investigated and applied to the design of wideband cross coupled filter. By extracting the coupling coefficient of various coupling structures and external quality factors of various feed structures, a SRR DGS four-pole filter with center frequency of 2.2 GHz and bandwidth of 20% is designed and fabricated. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A novel bandpass filter with two dual-mode cavities based on the substrate integrated waveguide (SIW) is presented. By making use of the inductive discontinuities in an SIW cavity, two degenerate modes can be excited. Due to the phase difference of the two modes in each cavity, two transmission zeros on each side of the passband are created, so the out-of-band rejection of the filter is significantly improved. An SIW dual-mode filter with a center frequency of 12 GHz has been fabricated and measured. The experimental results agree well with the simulation results. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A design method of tubular filter based on S-parameter curve-fitting method is presented, and a synthesis process from low-pass prototype to tubular band-pass filter is also analyzed. By using step-increasing theory, the curve-fitting process for designing tubular filter is proposed in particular. This method not only makes sure that the values of serial elements are accurate in each simulated process, but also reduces the factors which influence the values of shunted elements, and decreases the complexity in determining the element size. [ABSTRACT FROM AUTHOR]