Effect of Resistivity of ITO Thin Film When Used in Transparent Checkerboard Surfaces for RCS Reduction

Two periodic structures with particular reflection phase properties, when used in a checkerboard patterned arrangement, can lead to wideband reduction in radar cross-section. The individual periodic structures are to be designed such that the difference in the reflection phase of the two structures is around 180 degrees in the frequency band of interest. Phase cancellation results in the reduction in the backscattered RCS. For effective phase cancellation, it is necessary that the individual periodic structure is a high impedance surface (HIS). HIS can be realized using low loss substrates with highly conductive coating. Typical PCB substrates with copper layer can be used to realize such HIS. In this work, we investigate the use of indium titanium oxide (ITO) thin film for realizing transparent checkerboard patterned surfaces with RCS reduction capabilities. ITO is a transparent conducting oxide, having a trade-off between transparency and conductivity. Glass with dielectric constant epsilon(r) = 7.4 is used as the substrate. The effect on the reflection phase characteristics due to the resistivity of ITO thin film, patterned over glass substrate is investigated. A checkerboard patterned surface with copper coating, leading to 6 dB reduction in RCS in the X-band is used as the base design to demonstrate the effect of the resistivity of the ITO thin film. The transparent checkerboard patterned surface is fabricated using ITO coated glass and a suitable etching process to realize the patterned surface. Measurement of reduction in backscatter RCS in the X-band is carried out. Both measurement and simulation results demonstrate the transition of the periodic structure from an HIS to a resistive radar absorbing material, depending on the resistivity of the ITO thin film. Results confirm that the conductivity of the ITO thin film is a critical parameter, when used to realize checkerboard patterned surfaces for RCS reduction.