Low reflection sandwiched dipole array antenna used in high-loss liquids

In microwave imaging of biological objects, array antennas are desired for efficient- and swift-data acquisition. We have fabricated several kinds of dipole array antennas for microwave imaging of a human body by Chirp Pulse Microwave Computed Tomography (CP-MCT). Those antennas are consisted of more than 30 small dipole antennas so printed on a dielectric board as to construct a fan beam-type receiving antenna. The problem of such printed antennas is high return loss nature in high loss liquids such as a saline solution. We have tried to reduce the return loss by achieving the impedance matching between the antenna-conductor and surrounding saline solution (high-loss liquid) by covering the conductor with the same dielectric material as the printed dielectric board. The sandwiched dipole antenna works properly as we expected, but mutual coupling effects among adjacent dipole antennas have to be minimized for tomographic imaging. We have solved this problem by covering all the antenna conductors with small- and separate -dielectric substrates. Return loss of the sandwiched dipole antenna was reduced by more than 10 dB as compared to conventional printed dipole antennas.