Research On Passive Circuit In RF Front-end System

With the rapid upgrading of wireless communication technology,new requirements such as multi-band support,large bandwidth and anti-intrtference have been put forward for RF front-end devices.The dual-band power division circuit can be applied to different frequency bands of complex systems,which is beneficial to miniaturizing the device and improving system compatibility.The non-reciprocal filter strengthens the port isolation effect on the basis of the out-of-band suppression function,increasing the anti-in-band interference characteristic.Thus,it is of great value to study high-performance RF front-end passive circuits,and the main researches are as follows:The characteristics of the three power division topologies are compared and analyzed.The design of the two-way equal power division Wilkinson circuit and its isolation network are analyzed through the odd-even mode theory.The calculation formulas of the electrical coupling,magnetic coupling and the hybrid coupling are derived based on the equivalent lumped circuit model of the filter.The frequency response characteristics caused by the signal phase change in the CT,CQ and CT/CQ hybrid structure are analyzed.From the electromagnetic parameters of the ferrite material,the engineering selection method of the ferrite materials is given.The electromagnetic circuit theory and microwave network theory are used to analyze the three-port circulator to explore its working mechanism.Based on the dual-frequency T-segment,the dual-band performance of the structure is theoretically deduced and the realizability under large frequency ratios is analyzed.Through the Wilkinson division structure and the Chebyshev multi-section impedance transformation,a broadband dual-band power divider which can work in both centimeter wave and millimeter wave at the same time has been designed.Based on the ferrite column embedded microstrip structure,a dual Y-junction microstrip isolator has been designed.The equivalent model of the three-wire symmetric coupling unit is given,and the dual-mode resonator with center-loaded SIR is analyzed based on the odd-even mode theory.A miniaturized X-band filter with its performance debugging has been designed by ADS and HFSS.The out-of-band zero distribution can be independently controlled by the two SIR branches in the circuit.Using low-cost PCB technology,the non-reciprocal filter function has been realized in cascade mode.Based on the ferrite column external microstrip structure,an improved isolator has been designed.The lumped equivalent model of the 4-cavity CQ topology with capacitive cross-coupling is analyzed,and an out-of-band suppression enhanced filter has been designed.The X-band high-performance non-reciprocal filter function has been realized in cascade mode.In addition,a low-frequency ultra-wideband dual Y-junction isolator has been designed with a strip line structure and a medium filling method.