Study Of High Power Isolator For Wireless Systems

Both ferrite circulator and isolator play an important role in wireless RF communication system. Based on the nonreciprocity, ferrite circulator and isolator solve many practical problems, such as class isolation, impedance matching and antenna sharing in power amplifier and the radar. However, due to physical limitations of microwave ferrite materials, especially for these systems that are sensitive to the distortion, the nonlinear effects of microwave ferrite devices under high power can not be ignored. Therefore, for ferrite devices, study of nonlinearization and the improvements under high power are both important problems..To begin with, this paper researches the principle of ferrite circulator, analyzes the rotating magnetic property of ferrite material, precession equation and the influence of the material parameters on the performance. The detailed analysis of nonlinear phenomena of microwave ferrite and the discussion of various factors impacting the threshold power are included in this section and a number of measures for improvement are proposed.Secondly, this paper combines the measures to improve the nonlinearity of the whole system with the corresponding design theory of the double Y circulator and adapts the design idea of low-field working. The tools of matlab matlab and HFSS are used to calculate double Y junction structure parameters and magnetic parameters and analyze the influence of these factors on the final performance. All of these calculations are to provide accurate data for of sample making of low-field double-Y junction circulator and improve design efficiency.Finally, according to the above calculated parameters of the structural and magnetic, a ferrite double-Y junction isolator, whose center frequency and working bandwidth are respectively 2.01GHz and 1.91～2.11GHz, is developed. And then the CAD parameters are amended according to S parameters tested by Agilent E5071C .The final performances are basically consistent with HFSS calculations. The corresponding non-linear test platform is set up. Compared with the traditional devices operating under high field, according to two-tone IMD3 improved about 3dB, the ferrite devices working in low field have certain advantages on the linear side.