  This paper presents a slot antenna array with a reconfigurable radar cross
section (RCS). The antenna system is formed by combining a liquid absorber with
a 2*2 slot antenna array. The liquid absorber consists of a polymethyl
methacrylate (PMMA) container, a 45% ethanol layer, and a metal ground,which is
attached to the surface of the slot antenna array. The incident wave can be
absorbed by the absorber rather than reflected in other directions when the
PMMA container is filled with ethanol, which reduces the monostatic and
bistatic RCS. Thus the RCS of the antenna can be changed by injecting and
extracting ethanol while the antenna's radiation performance in terms of
bandwidth, radiation patterns and gain is well sustained. In a complex
communication system, this can be used to switch between detection and stealth
mode. The mechanism of the absorber is investigated. The simulated results show
that the antenna with this absorber has monostatic and bistatic RCS reduction
bands from 2.0 GHz to 18.0 GHz, a maximum RCS reduction of 35 dB with an
average RCS reduction of 13.28 dB. The antenna's operating band is 100 MHz.
Without ethanol, the antenna has a realized gain of 12.1 dBi, and it drops by 2
dB when the lossy ethanol is injected. The measured results agree well with the
simulated ones.
