초소형 마이크로스트립 Balun 필터

Abstract

The field of RF (radio frequency) and microwave is rapidly growing because of its use in wireless communication systems. In wireless applications, baluns which frequently connect a bandpass filter with a balanced component are

significant system factors but usually occupy much of the volume of the systems.Thus, with the speedy development of modern communication, reducing the size of balun is the main challenge in making RF systems compact. In addition, the poor balanced port matching and isolation performance of many conventional baluns limits their application.

In this thesis, a novel enhanced balun bandpass filter for extremely miniaturization is demonstrated utilizing the combination of diagonally shorted coupled lines and parallel end shorted coupled lines both with shunt lumped

capacitors. This method can largely reduce the required electrical length of transmission line, not only approximately maintaining the same characteristic

around the center frequency but also effectively suppressing the spurious passband.Meanwhile, a resistive network between the outputs is presented to realize the balanced matching and isolation. Comparing with the typical Marchand Balun, it takes better performance as well as shows a wider upper stopband.

Design equations and method is fully explained in this thesis. An extremely miniaturized balun filter operating at 1GHz of microstrip line form is fabricated on PCB substrate with 15 degree electrical length of the coupled lines. Both theoretical and measured performances are displayed. The experimental verification proves the usefulness of the proposed balun filter and its advantages of the application for mobile communications, etc.