For a preliminary study of detecting underground plastic mine, resonance behavior of the dielectric object is experimentally studied. A cylindrical plastic container having its diameter of 12.1 cm and height of 6.1 cm is filled with alcohol of its relative permittivity equal to 35. This plastic container is put in the water tank having its relative dielectric constant of 78 about 5.3 cm under the planar antenna in which two planar dipoles of transmitting and receiving are located and well isolated more than 55dB in the frequency range from 200 MHz to 3 GHz. Network analyzer is used to measure the transmission coefficients between two dipoles with the plastic container. This experiment shows the resonance of the structure by the periodicity in the measured frequency response, 436MHz, which corresponds to the ray path giving the transverse resonance. This gives the dimension of the dielectric target multiplied by the square root of its relative permittivity if the depth of the target is known.
