Capacitive coupling return loss of a new pre-ionized monopole plasma antenna

Plasma antenna has unique properties like low RCS and variable impedance; however, previous plasma antenna uses 500 MHz RF power to generate a plasma column, which is limited in energy efficiency and bandwidth. Here we introduce a new type of plasma antenna that generates plasma column with pre-ionization from a DC high voltage, and signal is coupled to the plasma antenna via capacitive coupling. This device greatly increases the overall energy efficiency and bandwidth of the plasma antenna. The electron density of the plasma is nearly constant in entire length, and is tunable in some degree by the DC current. Two plasma antenna of 1 m and 60 cm have been built and tested against same length metal antenna, the results are similar. Positive gain can be achieved at X-band. This device also shows a few obvious resonance lines where signal are absorbed strongly by the plasma. Return loss and radiation pattern of such antenna is reported.