Noise-factor dependence on mismatch of low-level r.f. signal

The r.f. impedance (v.s.w.r.) and conversion loss of X band Schottky-barrier diodes were calculated from d.c. analysis. For a broadband case, it is found that diodes having a v.s.w.r. of 1.3¿1.5 show a minimum conversion loss of 3.2 dB. These results are consistent with the experimental investigation, and show that matching a diode to the local-oscillator v.s.w.r. does not guarantee a correspondingly low conversion loss and low noise factor at the signal frequency. A matching to the low-level r.f. signal is required to obtain overall minimum conversion loss and noise figure.