Multi-band Microstrip Filter Based on Sierpinski Triangle Fractal

A multi-band filter based on Sherpinski fractal is presented. The filter has certain advantages in size and frequency band characteristics, and the working frequency band covers the L band, the S band and the C band. It consisted by stepped appearance and triangular patches. Through simulation analysis, the S-parameters of no fractal, first-order fractal and second-order fractal are compared in turn, and the effect of fractal structure on the filter can be seen. A fractal structure is introduced and ultra-wideband, multi-band and miniaturization can be achieved, which can improve insertion loss, return loss, bandwidth and reduce resonant frequency. After the fractal is improved, the center frequencies of the three bands are shifted to the low frequency band, and the passband's reflection coefficient is reduced from -28 dB to -37 dB, which optimizes system performance. The proposed filter has good crossover characteristics from 1.44 to 7.83 GHz, with the pass band range is 3.42 to 7.08 GHz, and the -3 dB FBW is 70%, which is ideal for WLAN requirements. At the same time, the stopband characteristics can also be applied to WIMAX to filter out interference signals. Another major feature after the use of the fractal structure is that the filter becomes more compact, the effective area is greatly reduced, and it is advantageous for miniaturization and integration. Based on the previous research, the fractal structure filter effectively implements multiple requirements such as multi-band, miniaturization, resonance frequency reduction and frequency band selection. The physical and actual measurements of the filter are performed, and the results of the vector network analyzer measurement filter are compared with the simulation results, and the measurement data agrees well with the simulation data.