Browsing by Author "Tang, S. -C."

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DUAL-WIDEBAND BANDPASS FILTERS WITH EXTENDED STOPBAND BASED ON COUPLED-LINE AND COUPLED THREE-LINE RESONATORS
(2012)
Kuo, J. -T.
;
Fan, C. -Y.
;
Tang, S. -C.
;
傳播研究所
;
Institute of Communication Studies
Coupled-line and coupled three-line resonators are proposed to design dual-wideband bandpass filters. Compared with the shorted and open stubs shunt at the same locations of the main line, in addition to saving the circuit area, these resonators provide alternative ways to the design of dual-wideband filters, with larger possible bandwidths and different frequency ratio of the two center passbands. The geometric parameters of the coupled-line and the coupled three-line structures are determined by deriving their equivalent circuits to a shunt open stub in parallel connection with a shunt shorted stub. To extend the upper stopband, a cross-shaped admittance inverter is devised to play the role of the 90-degree transmission line section at the center frequency and to create transmission zeros at the spurious passbands, so that the upper stopband of the filter can be extended. It is a quarter-wave section with two open stubs of unequal lengths shunt at its center. For demonstration, two dual-wideband bandpass filters operating at 900/1575 MHz and 900/2000 MHz are fabricated and measured. Measured results of the experimental circuits show good agreement with simulated responses.
QUASI-ELLIPTIC FUNCTION BANDPASS FILTER WITH UPPER STOPBAND EXTENSION AND HIGH REJECTION LEVEL USING CROSS-COUPLED STEPPEDIMPEDANCE RESONATORS
(2011)
Kuo, J. -T.
;
Tang, S. -C.
;
Lin, S. -H.
;
傳播研究所
;
Institute of Communication Studies
Planar microstrip filters are designed to have a quasielliptic function passband and extended upper stopband with a rejection level of 40 or 50 dB. The design employs stepped-impedance resonators in a compact 2 x 2 cross coupled configuration. The geometric parameters of the resonators are planned to shift the third resonance as high as possible, and then the transmission zeros created by the structure are devised to suppress the second resonance, so that a wide upper stopband up to more than 4.5 times the passband frequency can be achieved. By employing the skew-symmetric input/output feeds, three transmission zeros in the frequency band of interest can be created. The leading two zeros are allocated on the both sides of the passband, generating a quasi-elliptic function response with enhanced roll-off rate in the transition bands, and the last zero incorporating with a zero created by anti-coupled-line at higher frequencies are employed to extend the rejection bandwidth. The measurement data agree very well with the simulation responses.