Improved spatial resolution in thermography obtained by a two-layered structure of microstrip spirals

A receiving two-layered printed circuit antenna array concept is introduced for applications in thermography. In the design of the antenna structure, we have addressed the principle of using closely spaced and partially stack ed antennas to increase the transverse spatial resolution. The following as pects of the array construction and performance have been studied. First, t o which degree will stacking the antenna elements distort the respective ra diation patterns. Second, how to design the antenna elements in the back an d front layer for acceptably matching to a lossy medium in a broad frequenc y band. Third, to determine the mutual coupling between these closely space d antenna elements. By means of a scanning electric field probe, the radiat ed electric power distribution (E-2) was measured for a prototype two-layer antenna in a lossy homogeneous tissue equivalent medium. The measurements were parameterized in terms of two performance parameters defined in this w ork. In addition, the coupling properties were determined by means of the e lements S-11 and Sit in the scattering matrix. The analyses show that the p roposed concept performs according to some defined specifications over the frequency range from 1200 to 3000 MHz.