Based On The Tee Branch Line Of Microstrip Bandpass Filter Design And Analysis

With the rapid development and the growing need of satellite communications, electronic warfare and personal mobile communication, wireless communication technology are moving towards high-speed, high-capacity and multi-band. As a key component of the transceiver system, filter plays an important role. Especially in the receiver front-end, the performance of bandpass filter will directly affect the whole receiver. Therefore, the development of high performance and research in miniaturized filter are topics of concern in the field of microwave and millimeter-wave circuit. In this paper, we mainly study the conventional and balanced passband filters based on the T-shaped resonators.Firstly, we introduce the history of the development and research status of microwave filters briefly. The basic theory of microstrip transmission line and coupled microstrip line are presented. Some typical microstrip discontinuities that are often encountered in mocrostrip filter designs are described too.Secondly, two compact dual-band bandpass filters using T-shaped resonators are introduced. Dual-band bandpass filters for WLAN have been the focus of attention and design. Usually we use the coupling Stepped Impedance Resonators (SIR) to get two passbands separate from each other by adjusting the impedance ratio of the structure. However the T-shaped resonators in this paper get twice the impedance ratio under the condition of the same width ratio compared with the traditional SIR structure. So it can reduce the processing difficulty and make the controlling of center frequencies easier. For comparison, two different feeding structures are employed; the final filter has good performance for transmission.Then a kind of wide-stopband balanced bandpass filter is put forward. High integration and complex environment has been the main feature of modern microwave systems. Thus, there is not only a high-level of electromagnetic interaction between circuit nodes and crosstalk from substrate coupling between components, but also the interference from space. Therefore, the balanced circuit technology has become more and more important in the modern communication systems because of their good common-mode rejection capability. The balanced filter designed in this paper can broaden the stopband by adjusting the T-shaped resonators. To improve the common-mode suppression performance, two open stubs are connected with the outer T-shaped resonators.Two filters are fabricated and measured according to the theoretical design models. The good agreement between the measured and the simulated performance shows the validity of the theory analysis and the design process.