Design of Ring-Patch Pattern Based Microwave Frequency Selective and Infrared Camouflage Surface

The aircraft requiring microwave communication has a frequency-selective surface (FSS) that selectively transmits the electromagnetic waves of a specific frequency. However, an infrared (IR) signature is generated on the fuselage surface for reasons such as aerodynamic heating, and this infrared signature is directly related to the survivability of the aircraft. In addition, if the location where microwave transmission is required and the infrared signature reduction is required coincide, such as the radome (nose) and leading edges of an aircraft, the previously developed FSS pattern of infrared camouflage surface including metallic mirror can not be used. Therefore, we think that the coatings capable of selectively transmitting microwaves and controlling the infrared signature is needed. In general, a thin metal film cannot transmit microwaves because it acts as an electromagnetic mirror. For this reason, many researchers designed various FSS patterns so that only desired frequency can pass through, but the FSS surface they designed did not consider those infrared signature characteristics. Similarly, many researchers studying infrared emissivity control did not consider the selective transmission performance of microwave bands. For this reason, we first fabricated the aluminum (Al) thin films by thickness using sputter equipment (LSP-06, pressure 1mTorr, sputtering rate 3.4 nm/sec) to control the infrared emissivity. The thickness of the thin film we made was 5-500 nm, and we measured the infrared spectral emissivity in long-wavelength infrared (LWIR) band using FT-IR (Fourier Transform Infrared spectroscopy) and the infrared signature images using IR camera (FLIR a655sc). In addition, we designed an FSS pattern that includes the metal thin film and allows selective transmission in the X-band (8-12 GHz), which is mainly used for aerial vehicles communication. To this end, we designed the ring-patch patten based microwave FSS to have transmittance of 90% or more at a frequency of 10 GHz using numerical analysis (COMSOL Multiphysics, RF module). The ring-patch pattern FSS derived through numerical simulation was fabricated and the FSS performance in the X-band was experimentally verified using a lens horn antenna (X-band) and a vector network analyzer (Anritsu) device.