  A water-based switchable frequency selective rasorber with polarization
selectivity using the Great Wall structures is presented in this paper. The
proposed structure comprises a container containing horizontal and vertical
channels enabling dividable injection of water, and a cross-gap FSS. The
novelty of the design lies in its switchability among four different operating
states by injecting water or not into the water channels. When the container is
empty, the structure acts as a polarization-intensive FSS with a -0.42 dB
insertion loss passband at 3.75 GHz. When the horizontal channel is filled with
water and there is no water in the vertical channel, this structure can be used
as an FSR with single polarization selectivity. The FSR with -10 dB absorption
band from 6.8 GHz to 18.8 GHz only allows certain polarized electromagnetic
(EM) waves to pass at 3.1 GHz with an insertion loss of -0.78 dB, while another
polarized EM wave cannot pass. When the container is full of water, the
structure operates as an absorber with a reflection band below the absorption
band, where neither of polarization EM waves can transmit. Besides, a
reconfigurable water-based FSR automatic control system is built to achieve
state switching and temperature constancy of the water within the container.
Ultimately, a prototype of the presented design is fabricated, simulated and
measured to verify the feasibility. This work has potential application in
radome design to realize the out-of-band RCS reduction.
