Method and apparatus for transmission line and waveguide testing

Abstract

A multi-port junction is used in combination with an Inverse Fourier Transform to detect distance to fault in an RF transmission line or waveguide without the use of heterodyne down-conversion circuits. To provide an ultra-wide bandwidth frequency domain reflectometer the output ports of the multi-port junction are used to calculate distance to fault and return loss. The Inverse Fourier Transform algorithm is modified to take into account both phase shift per unit length of the transmission line and attenuation per unit of length in the transmission line, with the output of the modified Inverse Fourier Transform being applied to a module that subtracts out the effect of previous faults by solving for the distances ahead of time before knowing amplitudes and for solving for amplitude at each prior fault starting with the first fault. The output of this module is then used thresholded to remove the effects of noise, secondary reflections and inconsequential peaks. The result is a time domain waveform in which peak positions indicate the distance to real faults and in which return loss or percent reflection is calculated for each of the faults. Moreover, internal calibration loads and specialized processing are used to effortlessly calibrate the reflectometer in the field.