Cavity resonators for measurements with centimetre electromagnetic waves

A wave-meter for wave-lengths of about a centimetre, with an accuracy of 1 to 2 parts in 10 000, is described, based on a new system of coupling to the H 0 mode in resonant cavities which avoids the excitation of other modes. An indirect effect due to simultaneous resonance in two different modes is discussed in relation to the measurement of absorption by resonant cavities. The dielectric constants of six non-polar liquids have been determined, by means of wave-meters of this type, at wave-lengths of 3.2 and 1.35 cm. The values obtained at the two wave-lengths agree in all cases within 3 parts in 10 000, which is consistent with the estimated experimental error, and do not differ appreciably from the accepted low-frequency values. The temperature coefficient of the dielectric constant is compared with that calculated from the dilatation of the fluid. The power factors vary between 10 -4 and 2.10 -3 ; the higher values may be due to traces of polar impurity.