Using a mismatch transmission line to verify accuracy of a high performance noise figure measurement system

To verify noise figure measurement accuracy, an amplifier fully characterized by a reference laboratory may be used. The uncertainty of such a method is quite large because amplifier noise characteristics drift with temperature and time and quite sensitive to DC bias conditions. Since the noise characteristics of a passive 2-port network are directly related to its S-parameters, its measured noise figure can be directly traceable to S-parameter measurements. Passive 2-port devices such as matched through devices, isolators and 2-port networks that simulate the mismatch characteristics of an amplifier had been proposed. It had been demonstrated that no passive devices can fully verify the wide range of noise figure measurement conditions. More recently, the preferred verification method is to use a passive two port network cascaded with an amplifier. These passive 2-port networks typically provide a limited range of mismatch conditions that the amplifier interacts with and therefore do not fully quantify the operating range of a high performance noise figure measurement system. A mismatch transmission line (Beatty Line) provides a wide range of match conditions over a very wide bandwidth. This paper demonstrates how such a device can be used to verify a high performance noise figure measurement system.