Jie-Ming Qiu

High-Selectivity Low-Pass Filters With Ultrawide Stopband Based on Defected Ground Structures

Compact microstrip low-pass filters (LPFs) with ultrawide stopband based on a defected ground structure (DGS) and their design procedures are presented in this paper. A key merit of the filter configuration is that the selectivity of the LPFs can be conveniently controlled, whereas the bandwidth is fixed. The LPFs are realized using open-circuited uniform impedance stubs and stepped-impedance stubs (SISs). The position of the transmission zeros can be freely controlled by tuning the impedance ratio of the SISs. To expand the stopband, the dumbbell DGS is used to suppress the spurious passbands of the LPFs. Two demonstration filters with a cutoff frequency at 1 GHz have been designed, fabricated, and measured. The measured results indicate good performance: broad stopband (>15 fc or 20 fc) low passband insertion loss (<;0.3 dB), compact size, and sharp skirt characteristic.

Dual-Band Coaxial Cavity Bandpass Filter With Helical Feeding Structure and Mixed Coupling

In this letter, stepped-impedance resonators are used in coaxial cavity filter to generate dual-band response. Two key merits of the proposed filter are the helical feeding structure and the introduction of mixed coupling for coupling control and generation of transmission zero. The helical feeding structure makes it possible to conveniently control the external quality factors of two bands. To illustrate the concept, a third-order dual-band coaxial cavity filter is designed, fabricated and measured. The measured results are in good agreement with the full-wave simulation results.

Design of Microstrip Lowpass-Bandpass Triplexer With High Isolation

This letter proposes a lowpass-bandpass triplexer consisting of one lowpass channel and two bandpass channels. Stepped-impedance stubs are used in the lowpass filter (LPF) design, which bring a sharp selectivity. Defected ground structures are utilized to increase the impedance of one transmission line in the lowpass section, giving improved performance. High Isolation is achieved by careful consideration of the input signal splitting structure. To illustrate the concepts, a lowpass-bandpass triplexer is designed, fabricated and measured. The cut-off frequency of the LPF is chosen to be 1 GHz. The central passband frequencies are selected to be 2.4 and 5.8 GHz. Simulated and measured results are found to be in good agreement with each other. Isolations among the three bands are better than 40 dB.

Sharp-Rejection Wideband Bandstop Filter Using Stepped Impedance Resonators

A novel wideband bandstop filter is proposed in this paper. Using one uniform impedance resonator and two stepped impedance resonators, five transmission zeros are introduced in the stopband. Appropriate positioning of these zeros ensures the high selectivity and flat rejection level of the stopband. The bandwidth of the filter can be conveniently controlled by the characteristic impedances of the connecting lines and resonators. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for the bandstop filter are given in detail by using the lossless transmission line model. To illustrate the concept, a wideband bandstop filter with center frequency at 2 GHz and rejection level below 20 dB is fabricated. Theoretical, simulated, and measured results are found in good agreement with each other, and the measured 20-dB rejection bandwidth is as wide as 150%.

Design of quad-channel diplexer using short stub loaded resonator

Compact quad-channel diplexer (2.5/3.5GHz and 3/4GHz) using meandering short stub loaded resonators is proposed. The quad-channel diplexer is composed of two pairs of coupled short stub loaded resonators to obtain independently controlled bandwidth at each passband and to reduce the circuit size. In addition, the mixed electric and magnetic coupling is employed to create a desired transmission zero in the stopband, thus improving the isolation between each two passbands. The proposed diplexer is in final fabricated and measured. A good agreement between simulated and measured results evidently validates the proposed methodology.

Novel Matching Network and Its Application to Quad-Channel Diplexers

This letter reports a new kind of matching network for quad-channel diplexers. The matching network is comprised by some open- and short-circuited transmission lines, which can be chosen based on the design graph. The impact of loading resonators on the network is discussed. The diplexer can be easily realized by the combination of different bandpass filters without complicated tuning. To illustrate the concept, one quad-channel diplexer is designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other.

Compact cascade quadruplet bandpass filter with extend rejection bandwidth

This paper proposes a compact bandpass filter with excellent out-of-band performance. Stepped-impedance resonators (SIRs) are used to achieve an extended rejection bandwidth. Loaded stubs are also introduced to suppress the harmonic responses. The SIRs and the loaded stubs take up little extra room, and thus the proposed filter has a compact size. In this paper, a bandpass filter centered at 2 GHz is presented, with 20 dB rejection level up to about 16 GHz.

Low insertion loss bandpass filter with controllable transmission zeros using stepped impedance resonator

A transmission-line bandpass filter based on bandstop filter is proposed in this paper. A key merit of the filter configuration is that the position of the transmission zeros can be conveniently controlled whereas the bandwidth is fixed. The bandpass filter consists of two half-wavelength resonators, two open circuited uniform impedance resonators and one stepped impedance resonator. With five reflection zeros generated in the passband, six controllable transmission zeros are introduced to sharpen the passband skirts. Without coupling gaps between resonators, the new filter show low insertion loss and is easy for fabrication. To verify the design concept, one filter example has been designed, fabricated and measured. Good insertion/return losses, flat group delay, sharp transition and simple topology are achieved as demonstrated in both simulation and experiment.

Design of dual-band bandstop filter with low frequency ratio

This paper presents a dual-band bandstop filter by using stub-loaded resonators. The frequencies of the two stopbands are 1.6G and 2.4G, respectively, with the frequency ratio of 1.5. Several zero points are introduced, which significantly improve the skirt selectivity. The frequency ratio can be flexibly designed, and the fractional bandwidths of each stopband can be controlled conveniently. Moreover, high attenuation is achieved in both stopbands.