| dc.description.abstract | In this thesis, improving the passband performance of an absorptive bandstop filter (ABSF)is the target of this research. Two cases are considered. One is the insertion loss improvement of the lower passband, and the other is the bandwidth improvement of the upper passband. In addition, two different methods are proposed for improving the insertion loss of the lower passband.
First, design examples of single-band ABSF with lower passband insertion loss are realized on PCB. The stopband center frequency is 2 GHz. Additional open stub or stepped impedance inverter is used to improve the passband insertion loss while maintaining good stopband rejection. Specifically, by introducing an open stub to the conventional ABSF, one can improve the 0.5-dB insertion loss bandwidth of passband from dc-0.4 GHz to dc-0.5 GHz.. On the other hand, by using a stepped impedance inverter, one can reduce the insertion loss of passband with arbitrarily specified passband center frequencies. Two design examples are presented to validate the proposed design theory. For case A, the passband center frequency is 1 GHz and the insertion loss is improved from 0.92 dB to 0.36 dB. For case B, the passband center frequency is 0.67 GHz while the insertion loss is improved from 0.64 dB to 0.21 dB. Next, bridged-T coils are employed to replace the transmission line sections in the original designs so as to reduce the circuit area and achieve multi-band ABSF designs with lower passband insertion loss. Several design examples are realized in GaAs, WIPD and IPD process technologies to validate the proposed design method. Miniaturized single, dual, and triple band ABSFs with passband improvement are proposed. Compared with conventional designs, proposed single-band ABSF employing the open stub features a 1.3-dB insertion loss bandwidth from dc to 2.25 GHz, while that of the conventional design is from dc to 0.32 GHz. In addition, the proposed design with a stepped impedance inverter also features much better passband insertion loss as compared with the conventional designs. For the proposed single-band ABSF, the insertion loss at the passband center frequency of 2.4 GHz is improved from 1.1 dB to 0.66dB. For the proposed dual-band ABSF, the passband insertion loss at 2.4 GHz is improved from 1.88 dB to 0.83dB. For the proposed triple-band ABSF, the passband insertion loss at 2.4 GHz is improved from 3.43 dB to 1.4 dB. All of these circuits mentioned above have a better response in passband and a very compact circuit size.
Finally, ABSF with a wider upper passband bandwidth is proposed by increasing the frequency ratio of the spurious and of the fundamental stopband. The frequency ratio of the conventional ABSF design is 3:1, while the proposed design employing bridged-T coils features a frequency ratio of 4:1. In addition, the circuit area is also much reduced by using bridged-T coils for the ABSF design. | en_US |