Scattering parameters of a test fixture having a first port and a second port are measured by providing a test instrument; outputting a one-port reflection test signal from the test instrument to the first port with the second port terminated in a reflective termination having a known reflection coefficient, and receiving at the test instrument a one-port reflection measurement signal from the first port; subjecting the one-port reflection measurement signal to first time gating to generate a first time-gated measurement signal, the first time gating using a first gating function temporally disposed about the first port; subjecting the one-port reflection measurement signal to second time gating to generate a second time-gated measurement signal, the second time gating using a second gating function temporally disposed about the termination; and deriving the scattering parameters from the first time-gated measurement signal and the second time-gated measurement signal.