Jae-Hwan Shin

Semi-cylindrical Radar Absorbing Structures using Fiber-reinforced Composites and Conducting Polymers in the X-band

This paper presents a low observable structure with curved surfaces made by fiber-reinforced composites, conducting polymers and shows the possibility of developing stealth platforms for military applications. We propose radar absorbing structures (RAS) based on a circuit analog absorber in order to reduce the radar cross-section (RCS) of an object with curved surfaces. First, semi-cylindrical RAS with a periodic square patterned layer using a conducting polymer was designed and simulated by a commercial 3-D electromagnetic field analysis program. The designed semi-cylindrical structure with low RCS was then fabricated using fiber-reinforced composites and conducting polymer materials. Finally, the radar cross-section was measured in order to evaluate the radar absorbing performance of the fabricated RAS at a compact range facility. The measured radar absorption of the fabricated RAS showed that the targets RCS declined in a range of 65% to 94% within the X-band relative to a non-radar absorbing specimen.

ELECTROMAGNETIC WAVE ABSORBING TECHNIQUE USING PERIODIC PATTERNS FOR LOW RCS PATCH ARRAY ANTENNA

This paper presents an electromagnetic wave absorbing technique to reduce a radar cross-section (RCS) of a patch array antenna without compromising their antenna performance. The technique is based on periodic patterns, which is made of resistive materials. The 2×2 patch array antenna with a resonance frequency of 3.0 GHz was designed and fabricated. To reduce the RCS of the patch array antenna, the periodic patterns using a square patch element were proposed and applied to the surface between the four antenna patches. The printed lossy periodic patterns have radar absorbing performance at 12.0 GHz frequency. The measured results show that the lossy periodic patterns have no significant effect on the antenna radiation performance. On the other hand, the RCS is reduced by more than 98% compared to the conventional antenna at the target frequency.

Monostatic RCS Reduction by Gap-Fill with Epoxy/MWCNT in Groove Pattern

In this study, we investigated the effect of groove pattern and gap-fill with lossy materials at 15 GHz frequency of Ku-band. We used Epoxy/MWCNT composite materials as gap-fill materials. Although epoxy does not have an absorbance capability, epoxy added conductive fillers, which are multi-walled carbon nanotubes (MWCNT), can function as radar absorbing material. Specimens were fabricated with different MWCNT mass fractions (0, 0.5, 1.0, 2.0 wt%) and their permittivity in the Ku-band was measured using the waveguide technique. We investigated the effect of gap-fill on monostatic RCS by calculating RCS with and without gap-fill. For arbitrarily chosen thickness and experimentally obtained relative permittivity, we chose the relative permittivity of MWCNT at 2 wt% (e r =8.8?j2.4), which was the lowest reflection coefficient for given thickness of 3.3 ㎜ at V-pol. and 80° incident angle. We also checked the monostatic RCS and the field intensity inside the groove channel. In the case of H-pol, gap-fill was not affected by the monostatic RCS and magnitude was similar with or without gap-fill. However, in the case of V-pol, gap-fill effectively reduced the monostatic RCS. The field intensity inside the groove channel reveals that different RCS behaviors depend on the wave polarizations.