Improved Spatial Resolution in Thermography Obtained By a Two-Layered Structure of Microstrip Spirals

Abstract

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 stacked antennas to increase the transverse spatial resolution. The following aspects of the array construction and performance have been studied. First, to which degree will stacking the antenna elements distort the respective radiation patterns. Second, how to design the antenna elements in the back and front layer for acceptably matching to a lossy medium in a broad frequency band. Third, to determine the mutual coupling between these closely spaced antenna elements. By means of a scanning electric field probe, the radiated electric power distribution (E²) 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 work. In addition, the coupling properties were determined by means of the elements S₁₁ and S₁₂ in the scattering matrix. The analyses show that the proposed concept performs according to some defined specifications over the frequency range from 1200 to 3000 MHz.