A reconfigurable antenna using fluorescent lamps

Abstract

Plasma in a discharge tube, such as a fluorescent lamp, conducts electric current below a plasma frequency, and therefore can be used as an antenna element. This paper describes a reconfigurable antenna by combining a quarter-wavelength monopole on a ground plane and an array of U-shaped fluorescent lamps surrounding the monopole. The lamps configure as a square cylinder. When the lamps on adjacent two planes among the square cylinder are switched on, these lamps function as a square corner reflector; and when the lamps on a plane and approximately halves of its adjacent two planes are switched on, these function as a trough (C-shaped) reflector. These configurations yield a 8-multibeam, directional antenna. On the other hand, when all the lamps are switched off, this antenna is omnidirectional. An inexpensive reconfigurable antenna was realized by selecting the lamps to be switched on/off. Absolute gains measured with a prototype antenna were approximately 8.2-9.3 dBi when directional and 1.1-2.3 dBi when omnidirectional. Transient time between the different directivities was found approximately 60 ms, corresponding to the thermal time constant of hot cathodes of fluorescent lamps.