Analysis Of Parallel-coupled Microstrip Filter Based On Hybrid Fractal Structure

With the rapid development of millimeter wave technology,band-pass filters are crucial in RF front-end applications.Compared with traditional band-pass filters,parallelcoupled microstrip band-pass filters have the advantages of low cost and easy processing.However,the non-uniform characteristics between parallel coupled lines make the phase speeds of the even and odd modes different,resulting in this type The second harmonic of the filter is larger.As a novel filter,parallel coupled microstrip band-pass filter with fractal structure has important research value in realizing the second harmonic suppression of the filter.This paper uses two fractal structures and two miniaturized structures to improve four parallel coupled microstrip bandpass filters with different characteristics,the main research contents are as follows:In the first fractal structure,a new Minkowski fractal structure is first proposed based on the Minkowski fractal structure.Compared with the traditional Minkowski fractal structure,the new Minkowski fractal structure can better suppress the second harmonic.Secondly,in the miniaturized structure,the folded V-shaped structure and the in-line Wshaped structure are studied based on the traditional parallel coupled structure.Compared with the traditional parallel coupled structure,the folded V-shaped structure and the inline W-shaped structure can make the filter smaller size.Finally,based on the new Minkowski fractal structure,a microstrip band-pass filter with folded V-shaped structure and in-line W-shaped structure was designed.The center frequency of both filters is 2.4GHz,and the second harmonic peak level is 79.68 d B and 45.24 d B,respectively.Compared with traditional parallel-coupled microstrip band-pass filters,the area reduction rates of the two filters are 64.07% and 69.08%,respectively.In the second fractal structure,a novel hybrid fractal structure is first proposed based on the fractal structure of Koch and Minkowski.Compared with the traditional Koch fractal structure and Minkowski fractal structure,the hybrid fractal structure can better suppress the second harmonic wave.Secondly,based on the hybrid fractal structure,the microstrip band-pass filters with folded V-shaped structure and in-line W-shaped structure were designed.The center frequency of both filters is 2.4GHz,and the peak second harmonic levels are 50.58 d B and 28.94 d B,respectively.Compared with traditional parallel-coupled microstrip band-pass filters,the area reduction rates of the two filters are 64.07% and 69.08%,respectively.In this paper,the above filters are made in kind,and the test results are basically consistent with the simulation results,verifying the theoretical analysis and simulation results.Four parallel coupled microstrip band-pass filters with fractal structure prove that the research method of this paper is feasible.The research method of this paper achieves the expected research index,which lays a solid foundation for engineering practice,and has application value for the design and implementation of the 2.4GHz band wireless transceiver system.