Comprehensive Design And Research Of Novel Planar Equal-Corrugated Common Ratio Line Filters

With the rapid development of modern communication equipment,the communication system has higher and higher requirements on the performance of the filter,which is a key RF device.The filter with small size,high performance and easy processing has become a research hot spot.As a typical distributed device,all components of the common ratio line filter are transmission lines,and the electrical length is the same.Its design theory is complete,and the application frequency range is wide,which is suitable for microwave millimeter wave high frequency circuit,and has attracted much attention from researchers.Based on the coupled line structure,several common ratio line filters are designed in this thesis.The specific work contents are as follows:1.Based on the coupled line structure,a third-order low-pass filter topology is proposed,that is,a uniform transmission line is connected between two non-adjacent ends of the coupled transmission line.The filter comprehensive analysis method is applied to the design of the structure,the transmission function is derived,and the objective function is constructed.Then,according to the preset index,the impedance values of each component are obtained by solving the equation,and the specific performance of the filter structure is discussed.The simulation results show that the structure can realize the tun-ability of out-of-band suppression by changing the coupling coefficient k while keeping the in-band response of equal ripple unchanged.2.On the basis of the above third-order low-pass filter,two kinds of fifth-order low-pass filter structures based on coupled-lines are proposed.The first structure is to cascade two open-circuit branches at both ends of the uniform transmission line,and the second is to parallel two homogeneous transmission lines with the same characteristic impedance between two non-adjacent ends of the coupled-line.The transmission functions of the two structures are derived in detail.The comprehensive design results show that the fifth-order low-pass filter structure broadens the tuning range of the bandwidth and improves the out-of-band suppression ability.3.Combining the structures of the two fifth order low-pass filters,a seventh order low-pass filter with open-circuit branch loading is proposed.The comprehensive design results show that the filter increases the transmission zero outside the band,has wider bandwidth tuning range and steeper side-band suppression,and has good filtering performance.In addition,the structure can not only realize the adjustment of the out-of-band suppression level while keeping the in-band wave-frequency response unchanged,but also optimize the in-band matching situation without changing the out-of-band suppression level by adjusting the k value.