PURPOSE: To lessen dispersion of noises over a series of frequencies compared with a conventional method, establish accurate measurement of a group delay, and reduce the distortion of the trace from the conventional level.

CONSTITUTION: The phase response of a network is measured at uniform frequency intervals. A linear regression analysis 54 is executed for a sample of phase response measured with a number of frequencies in an aperture centering on the group delay frequency. A prediction value for group delay of network at that frequency is acquired. This processing cycle is repeated for a series of group delay frequencies (52-58), and a trace for the group delay of network over a certain scope is determined.