Method for measuring noise parameters of microwave two-port - Electronics Letters

Introduction; The measurement of the four noise parameters ("s) NPs of a two-port in the microwave frequency range is usually performed by measuring the two-port device noise figure F for a minimum of four source reflection-coefficients r,, produced with a tuner connected at the two-port input (reflection-type tuner) [I ~ 61. The equation relating F and rs, ( i = 1, ..., N) is expressed in linear form, and the resulting overdetermined linear equation system is solved for the NPs [I, 2, 51. A number of measurement methods have been proposed. In 131, F(rst) is determined from the measured r,, and the corresponding noise powers delivered by the two-port to the receiver, at room temperature. The system gain is computed from the hot and cold noise powers delivered by a two-state noise-source 13, 71. Equal hot and cold source reflection-coefficients vsH = rs,) must be assumed. Typically, this assumption does not affect the measurement accuracy of the NPs, because the differences between r,, and rs, are very small, but some applications (for example, cryogenic measurements or radiometer calibration) may require different hot and cold loads. In 141, a method is given that avoids the former restriction by using an alternative measurement magnitude, i.e. the ratio between the delivered noise powers and a mismatch coeffcient. Only the hot-source measurement is required to determine the system gain, but it is implicitly assumed that the cold (room) temperature, T,, equals the reference temperature, To (= 290K) [4]. This assumption is a limitation in a real laboratory environment, or whenever the tuner includes semiconductor (PIN diode) switches, because the diodes add a non-thermal (shot) contribution to the temperatures of the tuner states, T,, ( i = 1, ..., N). Alternative techniques to measure the four N p s for the particular case of a transistor 181, make use of the transistor equivalent circuit as additional information. However, a tuner must be used to calibrate the receiver noise.