Precise Location of Passive Inter-Modulation in Long Cables by Fractional Frequencies Based Multi-Range Rulers

Abstract: A novel method is developed by utilizing the fractional frequencies based multi-range rulers to precisely position the passive inter-modulation (PIM) sources within radio-frequency (RF) cables. The proposed method investigates a set of fractional frequencies to create multiple measuring rulers with different metric ranges to determine the values of the tens, ones, tenths, and hundredths digits of the distance. Among these rulers, the one with the lowest frequency determines the maximum metric range, while the one with the highest frequency decides the highest achievable accuracy of the position system. For all rulers, the metric accuracy is uniquely determined by the phase accuracy of the detected PIM signals. With the all-phase Fourier transform method, the phases of the PIM signals at all fractional frequencies maintain almost the same accuracy, approximately 1°(about 1/360 wavelength in the positioning accuracy) at the signal-to-noise ratio (SNR) of 10 dB. Numerical simulations verify the effectiveness of the proposed method, improving the positioning accuracy of the cable PIM up to a millimeter level with the highest fractional frequency operating at 200 MHz.

Keywords: passive inter-modulation; location; multi-range