On measurement of reverberation chamber time constant and related curve fitting techniques

The reverberation chamber time constant quantifies how fast a reverberation chamber loses its stored energy at different frequencies, which makes it a very important parameter in many power related tests, such as the measurement of antenna efficiency, the measurement of absorption cross section, and the electromagnetic immunity test of electronic devices. The chamber time constant is usually obtained by doing regressions of power delay profile and calculating its gradient. But the shape of power delay profile can sometimes be distorted by the band limited window function applied in the frequency domain. A non-linear curve fitting technique which can cancel the effect of window function was developed, aiming to give a robust determination of the chamber time constant. With the help of this technique, window functions with much smaller bandwidth can be applied without introducing error in the evaluation of chamber time constant. In this paper, a 1 MHz wide window function in which only 10 samples of S21 are available was put under test and it was found a robust answer of chamber time constant can still be given by non-linear curve fitting techniques. Therefore the measurement time can be reduced and the frequency resolution of the chamber time constant can be increased at the same time.