Broad-Band Microwave Transmission Characteristics from a Single Measurement of the Transient Response

A technique is presented for the measurement of the transmission and reflection scattering coefficients of microwave networks by Fourier analysis of the sampled transient response of the network to impulsive or steplike waveforms. It is demonstrated that the method can reduce errors due to mismatch of the components of the measurment system by sampling the response over a finite time domain window that excludes unwanted reflected components. A review is made of the errors introduced due to aliasing, truncation, and noiselike sources such as timing jitter and additive noise, and a description is then given of an experimental system to evaluate the technique, based on use of a 12-GHz sampling oscilloscope for measurement of the transient response and a suitable form of the fast Fourier transform algorithm. Measurements on some typical wide-band components are presented, and it is concluded that for very broad-band measurements with moderate resolution the method has a potential accuracy of about ±0.1 dB and ±1°, with a significant reduction in mismatch errors.