X-band microwave antenna with a switchable planar plasma reflector

We present a test of a switchable X-band microwave plasma antenna having an aperture diameter of 30 cm. The dense plasma which forms a reflective surface is produced by a ferromagnetic inductively coupled plasma source. A planar-convex dielectric lens placed at the top of the vacuum chamber forms the required phase front of the reflected electromagnetic wave and simultaneously serves as a vacuum cap. The antenna gain is just a bit (about 1 dB) less than that of an ordinary microwave antenna with the same diameter. When the plasma is switched off (off-state), the antenna radar cross section was found to be at least 20 dB smaller as compared to the on-state.