Synthesis And Design Of Microstrip Dual-band Bandpss Filter

Nowadays, with the rapid development of communication technology, the emergence of new communication standards, and the high miniaturization and integration of communication equipments, the filter as one of the most important components in electronic communication equipment, needs to satisfy higher requirements in the face of the challenge of the communication standard integration. At the same time, the multi-band bandpass filter, especially the miniaturized multi-band filter has gained the attentions of many researchers. Since the beginning of 1990 s, a lot of novel methods for designs of dual-band bandpass filters, which is the basis of multiple bandpass filter research, have been emerged. In this thesis, a miniaturized dual-band bandpass filter is designed by the traditional synthesis design method and coupling theory. The main innovation work is as follows:1. A miniaturized dual-band bandpass filter is designed by improved uniform coupled lines. The L-shaped coupled line structure is composed of open-ended stubs and uniform coupled lines with the electrical length of λ/4. The L-shaped coupled line structure has virtual bandpass filter response characteristic. A stopband is caused by open-ended stubs at the ports, which make the original virtual bandpass filter has a dual-band bandpass response. The structure could be more compact by bending the open-ended stubs. In addition, shorting the length of the coupling lines can reduce the electrical size and improve stopband performance of the filter.2. Frequency selective characteristic and isolation between the two bandpass are enhanced by loading the stepped-impedance stubs. The stepped-impedance stubs are loaded to the L-shaped coupled line directly, which makes the original virtual bandpass filter bandwidth become narrow. At the same time, one transmission zero and one transmission pole are produced. By adjusting the size of the coupling line and stepped-impedance stubs, properly, a dual-band bandpass filter with two transmission zeros between two passbands can be achieved. The filter also has the structure characteristic of miniaturization.3. A third-order chebyshev type dual-band bandpass filter is realized by the dual-band bandpass lumped circuit, combined with J transformation using the π type network. The hybrid resonant circuit is equivalently analyzed by using λ/4 open-ended stubs and λ/4 short-ended stubs. Finally the stepped-impedance short-ended stub is equivalent to the parallel resonant circuit, and all the stubs are directly connected to both sides of the main transmission lies in parallel, rather than a staggered arrangement. With all of these strucures above, the hybrid integrated bandpass and bandstop filter is achieved, and miniaturization design is also realized.