A complementary-defected ground structure (DGS) common stopband filter is proposed. The filter uses two kinds of DGS patterns: a Π-shaped DGS pattern is used in both sides of the filter and a button-headed H-shaped DGS pattern is adopted at the middle of the filter. The filter utilizes the mutual inductance and mutual capacitance that exists among the DGS patterns to improve the in-band gain-flatness of the filter, which is useful to broaden the bandwidth and improve the rejection ratio in the low cutoff frequency. The simulated and measured results show that the differential signal under the DGS filter is nearly intact and the common-mode noise can be reduced by 15 dB from 3.2 to 12.4 GHz. The area of the filter is only 10 mm × 10 mm. The fractional bandwidth of the stopband can reach 118%.
A wideband common-mode (CM) suppression reconfigurable filter is proposed for high-speed all-pass differential circuits. The filter adopts three varactor-loaded compact defected ground structures (DGSs) to achieve continuous reconfigurability in its operation frequency with a large CM suppression dynamic range in the bandwidth. The varactors play an important role in widening the accessible instantaneous bandwidth and miniaturizing the structure. The three DGS cells with a total area of 15 mm x 10 mm are implemented symmetrically under the differential lines, to obtain reconfigurable CM bandstop characteristics which can be continuously adjusted from 1.8 to 8.1 GHz. A coupled LC resonator equivalent model is developed to represent and analyze the proposed filter, which explains its operation principle and assists in accelerating the reconfiguration design method. A good agreement between full-wave simulations and measured results is demonstrated, which validates the proposed design. INDEX TERMS Reconfigurable filter, defected ground structures, common-mode suppression, varactor diode.
In this paper, a compact quintuple notched-band ultra-wideband bandpass filter with high selectivity and wide bandwidth is proposed. The filter adopts an approximate closed-loop C-shaped stepped impedance resonator to generate triple notched bands, and uses Hilbert fractal curve slit and L-shaped resonator to create single notched band, respectively. Multiple notched-band are centered at 5.29, 6.61, 7.92, 8.95, and 9.93 GHz to eliminate undesired interference from coexisting wireless services of WLAN, C-band, and X-band. Additionally, two transmission zeros are introduced to enhance the sharp skirt selectivity up to 0.944. This filter could exhibit high sharp selectivity and wider bandwidth simultaneously. The filter is fabricated on a RT/Duroid 5880 substrate (ɛ
r
= 2.2 and thickness = 0.787 mm) and measured to verify the simulation results. Both simulation and measurement are in well agreement, showing the good performance of the filter.
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