The Dielectric Constant of Dry Air

A sensitive and accurate method for determining the real part of the dielectric constant of gases at microwave frequencies is described. The method eliminates some possible sources of systematic error inherent in earlier methods. The dielectric constant of dry air at N.T.P. has been determined as 1.000569, at a frequency of 3000 Mc/sec. This is in good agreement with other results, at 24,000 Mc/sec, at 9000 Mc/sec, and at low frequencies, thus verifying that the dielectric constant is independent of frequency up to nearly 30,000 Mc/sec An earlier result suggesting the contrary was found to be in error because of insufficient drying of the air.