Study Of Passive Intermodulation Interference At Microwave And RF Frequencies

The phenomenon of intermodulation generation due to transmission of multiple carriers through passive components is generally called passive intermodulation (PIM for short). PIM products in high-power multiple-channel communication systems have become one of the spurious interference. In this paper, PIM interference at microwave and RF frequencies is studied. The generation causes, effects on communication systems and possible mitigation measures of PIM are explored. A method for predicting PIM amplitude and power level is presented. PIM properties in mobile communication and communication satellite systems are analyzed.The generation mechanism and mitigation measures of PIM are discussed. PIM interferences at microwave and RF frequencies are mainly originated from two types of passive nonlinearities, namely, the contact non-linearity and material non-linearity. The former refers to any metallic contacts which have nonlinear current-voltage behavior. The later represents bulk materials which exhibit nonlinear current-voltage characteristics.The general nature of intermodulation products is discussed. A general instantaneous transfer function for a nonlinear device is assumed and it is decomposed into odd and even terms in order to calculate the concrete forms of intermodulation products. General formulas of the amplitude of intermodulation products as a function of intermodulation orders in two-carrier case are derived by applying Fourier series method. Numerical computation of the amplitude of intermodultion products in two-carrier case as to two typical transfer functions, piecewise linear soft limiter and smooth soft limiter, is implemented. Analysis and numerical results indicate that the amplitude of intermodultion products generally decrease with the increase of intermodulation order. The decreasing behavior of higher order intermodulation depends essentially on the type of transfer function.PIM problem is simplified by considering an assumption of composite interference model and characteristic function method. An analysis is made of the statistical features of the total interference including PIM interference. Furthermore, a numerical simulation is carried out to the effects of PIM on the anti-noise property of communication systems. Analysis and simulation results show that tail distribution is very different from Gaussian; the effects of passive intermodulation interference oncommunication systems are mainly in the region of low bit error rates.A general formula is derived by using power series by which we can predict the amplitude and power level of PIM (especially for odd-order PIM). General ideas and methods of predicting higher-order PIM power level with the experimental results of lower-order PIM power level are proposed. Prediction of the fifth order PIM power level with the third order measurement value is realized by computer program. Calculated values are compared with experimental results indicating that the obtained theory is right and practical. In addition, the IM power delivered to the load and the third order IM variation with carrier power ratio are discussed.Passive intermodulation interference in mobile communication system is analyzed. PIM distortion generated within cable assemblies in mobile base station is described by applying two point source models. Passive Intermodulation Properties of mobile communication antenna is discussed. The measurement regarding passive intermodulation in mobile communication system is introduced. Some rudimentary measurements are carried out.Passive intermodulation interference in communication satellite system is analyzed and calculated. By analyzing a practical example of satellite system at C band, every individual channel is simulated as one flat signal-power spectrum and the autocorrelation function of the uniform power distribution can be easily found. A formula for evaluating the power spectral density of nth-order passive intermodulation distortion can be derived by Fourier transform. The degree of PIM interference can be understood better by compa...