| Summary: | 碩士 === 國立中正大學 === 電機工程所 === 97 === This thesis investigates bandpass filters with respectively tunable center frequency and bandwidths. The tuning capability is generated from the control of varactor reactance on a dual-mode closed-loop resonator, whereas the perturbation intensity of the resonator is changed to separate the even and odd mode’s resonator frequencies. The input and output feeding network must be modified simultaneously to achieve theoretically perfect impedance match. Three tuning functions are accomplished: a) tunable center frequency with a fixed fractional passband width (FBW), b) tunable center frequency with a fixed absolute passband width, and c)tunable fractional bandwidth with a fixed center frequency. Two realization configurations of the perturbation varactor are also presented, which are four-point and three-point perturbation of the ring resonator. The tuning theory, design formula, and measurements are performed in the thesis.
On the four-point perturbation configuration, for the tuning function a, the measured tuning range is from 0.7 GHz to 1.26 GHz with 15% FBW. The insertion loss is 2.8-3.1dB and the return losses are greater than 17 dB. For the tuning function b, the tuning range is from 0.7 to 1.2GHz with fixed absolute bandwidth of 130MHz. The insertion loss is 2.8-3.2dB and the return losses are better than 10 dB. For the tuning function c, the FBW can be tuned from 12 to 26% with the fixed center frequency of 1 GHz. The insertion loss is 2-3dB with the return losses better than 10dB.
On the three-point perturbation configuration, the tuning function a has the measured tuning range from 0.79 GHz to 1.19 GHz with 15% FBW. The insertion loss is 2.9-3.1dB and the return losses are greater than 20 dB. The tuning function b has the tuning range is from 0.78 to 1.16 GHz with fixed absolute bandwidth of 130MHz. The insertion loss is 2.8-3.2dB and the return losses are better than 23 dB. The tuning function c has the FBW tunable from 13 to 51% with the fixed center frequency of 1 GHz. The insertion loss is 1.8-3.0 dB.
From the theoretical and measurement results, this thesis successfully demonstrates two novel types of tunable bandpass filters, each having three tuning functions. The four-point perturbation type bandpass filter has a largest center frequency tuning range, while the three-point type has the largest tuning range of fractional bandwidth ratio.
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