Rerearch And Design Of Multi-band Directional Coupler

In recent years, with the rapid development and extensive use of mobile communication system, the study and design of the miniaturized and multi-band passive microwave components have become the key topic of modern scientific research. So research of miniaturized and multi-band directional coupler, as the important elements in such kind of system, has become one of the focused orientation of microwave components in the present. Based on the research background above, two kinds of dual-band directional couplers with novel structure using two common forms of transmission line and traditional method on design and research have been achieved in this thesis.A novel dual-band, branch-line coupler based on microstrip line is presented in this paper firstly. The proposed coupler consists of two-layer, back-to-back substrates, whose structure is different from the conventional ones, and maintains the characteristics of miniaturization and dual-banded, etc. The length of the proposed coupler can be adjusted flexibly according to the different band requirements in the practical application. According to the simulated results, the center frequency of the operating band of the fabricated coupler with good performance is 3.4 and 4.4 GHz. A series of simulations pointed at its length have been achieved to analyze the effects of different length on its features adequately.Another novel dual-band, branch-line coupler based on stripline with 90° phase difference is presented in this paper secondly. The proposed coupler consists of three quarter-wave coupled-line sections, which is unlike the conventional ones, with a small size and wide frequency band characteristics, etc. The center frequency of the operating band of the fabricated coupler is 2.0 and 4.1 GHz, with 90° phase difference between the coupled end and the through end and perfect performance on the simulated results. It is very convenient to achieve the miniaturization design of the coupled-line sections in this coupler to some extend using the equivalent T-type structure.Because of the immature research on tri-band and multi-band coupler, only the designmethod is discussed in this thesis, such as stub matching method, etc.Although the structure of the designed dual-band microstrip directional coupler is novel in this paper, but the processing and the performance need to be further improved. The research of multi-band directional coupler should gradually rise from theory to practice, taking some new characteristics into account, such as variable frequency, etc.