Low-cost computer-based time-domain microwave network analyser

An inexpensive time-domain automatic network analyser (t.d.a.n.a.), with a frequency bandwidth extending up to 10GHz, is described. This analyser is valuable for performing amplitude and phase measurements on broad-band systems with an accuracy of a few degrees in phase and a dynamic range of 35dB or better. Measurements are performed in the time domain with the aid of a sampling oscilloscope and the corresponding frequency-domain information is obtained using a numerical processor and fast-fourier-transform (f.f.t.) algorithm. To avoid significant errors occuring in the f.f.t., the choice of the time-domain pulse-excitation waveform is discussed in the light of discrete-fourier-transform (d.f.t.) theory. The system is evaluated by the examination of calibrated microwave filters.