Study On Miniaturized Rat-Race Couplers For Microwave Communication Systems

With the rapid development of electronic information systems to multifunction, miniaturization, and low cost etc., there are more and more urgent demands on high performance miniaturized microwave passive components for system on package (SoP) technology. Thus, it is necessary to develop new integration techniques for microwave passives in SoP with high performance, high integration density, good compatibility, low loss and high power handling capability. For such a purpose, this work is mainly focused on the miniaturization of rat-race couplers, one type of key passive components used in microwave communication systems. The main content of this thesis is summarized as follows.1) The conventional rat-race coupler is first introduced. Then, the design equations are derived for rat-race couplers without and with a phase inverter, respectively.2) The design equations for a phase reversal with coupled lines are extended to the more generalized forms. A phase inverter is realized by a modified Lange coupling structure with a slotted ground plane and a floating-potential conductor. A 0.64λmicrostrip rat-race coupler with modified Lange phase inverter operating at 2.0 GHz is designed. In order to further miniaturize the rat-race coupler, a 0.52λmicrostrip rat-race coupler also based on T-shaped line is designed at 2.0 GHz. The bandwidths of two couplers for in-phase and out-of phase states are both enhanced.3) Based on the design equations of a rat-race coupler with a phase inverter, a dual-band rat-race coupler is designed for 0.9/1.8 GHz application with double-sided parallel-strip line (DSPSL). The design equations for dual-band stepped-impedance rat-race coupler are derived, and a compact prototype is developed. In order to further miniaturize the dual-band rat-race coupler, both stepped-impedance sections and open stubs are utilized. A dual-band characteristic is achieved for a 0.9/1.8 GHz dual-band rat-race couper with its circumference of 0.44λ.In the above researches, a number of different prototypes are designed and fabricated. The validity and efficiency of this investigation have been demonstrated by the reasonable agreement between the measured and simulated results.