Measurement of the electrical constitutive parameters of materials using antennas, part II

The previously developed technique for measuring the electrical constitutive parameters of materials using a single monopole antenna is extended to include a monopole with closely spaced parasitic elements. The addition of the parasitic elements reduces the radiation from the antenna and, in turn, reduces the effect of reflections from material boundaries on the measurement. This allows smaller volumes of material and smaller image planes to be used when measuring materials with low dissipation. A simple measurement procedure is presented for a monopole with two symmetrically located parasitic elements. The procedure is based on the representation of the normalized impedance of the antenna by a rational function of order three. It is applicable for frequencies at which
\|kh\|
(wavenumber-length of antenna) in the medium is less than that for resonance in a lossless medium,
\|kh\| \lesssim \beta_{r}h
. The design of a practical probe for the in situ measurement of soils is described and its use is illustrated.