A switchable microwave reflector, reflection of which is actively controlled using diodes was proposed. Pin diodes have large resistance and capacitance without DC bias and small resistance and inductance with DC bias in microwave band. The reflector was designed by using the characteristics. In this paper, effects of a periodic structure on the reflector were verified with simulation and equivalent circuit model. A prototype reflector was able to switch between about $-20$ dB and $-0.1$ dB reflection coefficient at 2 GHz.

Radar cross section (RCS) of a patch array antenna is reduced using a switchable absorption/transmission surface. The switchable surface performs as between a radar absorber and transmission surface using diodes at 9GHz. The switchable surface was applied to the radome of a patch array and its radiation pattern and RCS reduction were evaluated. The gain and the radiation pattern with the radome was equivalent to that without the radome. The RCS reduction with the radome was 25dB compared to that without the radome.

Vertical- and horizontal-polarization RCS of a dipole antenna was reduced using a switchable reflector. The switchable reflector can switch reflection level for the vertical-polarization and have absorption for the horizontal-polarization. The reflection level of the reflector for the vertical-polarization can be switched using pin diodes and the reflection for the horizontal-polarization can be reduced using resistor on the surface. The switchable reflector was designed to operate at 9 GHz and fabricated. The vertical-polarized reflection coefficient was switched -28 dB with OFF-state diodes and -0.7 dB with ON-state diodes, and horizontal-polarized one was less than -18 dB at 9 GHz. The reflector with ON-state diodes was applied to an antenna reflector of a dipole antenna and comparable radiation pattern to that with a metal reflector was obtained at 9 GHz. Moreover the reflector with OFF-state diodes was applied to the reflector of the dipole antenna and the RCS of the dipole antenna was reduced 18 dB for the vertical-polarization and 16 dB for the horizontal-polarization. Therefore the designed switchable reflector can contribute to antenna RCS reduction for dual-polarization at the operating frequency without degrading antenna performance.