Dielectric layer thickness measurement - uses broadband microwave pulses which are detected by horn antenna

摘要

The pulse generator (1) has a rise time of less than 1 nS which generates pulses having Fourier components in the microwave region and a band-width of more than 1 GHz. The pulses are transferred by a coaxial conductor and a coaxial waveguide to a transmitting aerial (2) which may be an X-band horn antenna. The pulses are reflected by dielectric layers (D1, D2) spaced between 0.5 and 10 m from the aerial and the reflected radiation is collected by a receiving aerial (3) which may be of similar construction to that of the transmitting aerial. The radiation passes by a coaxial line to a sampling head (4) where it is periodically examined by means of an oscilloscope (5) or pen recorder to derive an indication of the thickness and dielectric properties of the layers (D1, D2).