Transmission Line Pim Technology Research Under The Condition Of High Power

Passive Inter Modulation, PIM for short, is the new frequency component generated by two or more frequencies mixed in passive components(or linear devices), and it widely exists in high-power, multi-channel microwave communication systems. The generation of Passive Inter Modulation is closely related to the nonlinearity of passive components triggered under high power condition. Its appearance will produce in the air or within the system a set of useless frequency spectrum which also affects the regular work of the system. Based on a high power sampling device in a high power traveling wave tube amplifier nonlinear spectrum test system, this paper studies the Passive Inter-modulation characteristics of strip line, which will be beneficial for the analysis of the nonlinear spectrum test result for the traveling wave tube amplifier.This paper first describes the research background, introducing the domestic and overseas studies of Passive Inter Modulation developments, with a discussion on the performance characteristics of Passive Inter Modulation. It also analyzes the internal mechanism of Passive Inter Modulation generation, and describes effective measures to reduce Passive Inter Modulation in projects.Secondly, the paper also analyzes classical nonlinear transmission line NTL(Nonlinear Transmission Line) model, establishes the nonlinear resistance physical model of transmission line and conducts analysis, formula derivation and data simulation of the nonlinear characteristics due to self-heating in the strip-line metal conductor. With a discussion on Passive Inter-modulation test requirements and programs, in accordance with the test target and testing conditions, the paper has presented the contrast test programs for strip-line’s weak PIM characteristics. Using three different signal acquisition modes such as strip line sampling plat-form, attenuators and couplers, spectrum test will be conducted on harmonic wave under different output power and the third-order inter-modulation of the amplifier; changing the join order of low pass filter and strip sampling device after the amplifier output, spectrum test will be conducted on the second-order harmonic wave under the conditions of different power. Through a comparison of test data, confirmatory studies will be conducted on strip line’s nonlinear functions.Besides, simulation design and production is completed for at least one wavelength cycle strip-line sampling device including coaxial probe, broadband strip-line and strip-line to APC- 7 transition structure working in the 2~18 GHz. As the reflection coefficient of the strip-line are increased compared to the simulation, errors are positioned and analyzed through the time-domain function of vector network analyzer, providing a basis for further improvement.Finally, finish assembling test systems according to the pre-designed test program and complete spectrum test on the harmonic wave and the third-order inter-modulation of the amplifier. Test results show that under the condition of maximum 33 dBm power, the strip-line’s nonlinear features performance is weak, in accordance with the theoretical analysis.