Spectrum sharing and dynamic band allocation remain significant barriers for the next generation communication systems and sensors. In this regard, development of reconfigurable radio-frequency (RF) systems is increasingly important. However, most of the existing and proposed technologies tend to be primarily beneficial to reconfigurable receivers or low-power transmitters. Indeed, conventional semiconductor devices are easily damaged and have challenging interference and linearity issues when the power level exceeds a few Watts, while mechanically-tunable systems are bulky and slow. In this regard, weakly ionized plasmas can offer an attractive solution. Plasma-based electronics are inherently capable of handling high power. Focusing on novel methods of generation and control of weakly ionized plasmas, the proposed effort could create a foundation for rapidly tunable, low-loss, high-power transmitters and radar systems from the MHz to the GHz range.
To demonstrate this potential, the proposed effort will investigate regimes of weakly ionized plasmas conducive to their use as switchable and tunable elements in RF antennas. The novel concepts distinguishing this program are: (1) the use of plasmas as both tunable dielectrics and conductors; (2) plasma generation by nanosecond repetitive pulses that would enable low thermal electromagnetic noise and low ohmic losses. As electrical conductors, low temperature plasmas, such as those in glow and similar discharges, can potentially be used in RF antennas, amplifiers, and filters. The inherent advantages of plasma antennas or antenna elements include the possibility of turning the antennas on/off and also rapidly changing the antenna properties such as the resonant frequency. Large, meter-scale, plasma antennas have been previously demonstrated, and with the development of microplasma technology, plasma antennas can be miniaturized. However, three fundamental issues present stumbling blocks for the development of plasma-reconfigurable RF systems: a) the inherently lower conductivity and thus higher losses of plasmas compared with metals, b) the high power consumption and heat generation, and c) the high electron temperature translating into much higher thermal electromagnetic noise in plasma devices compared with solid state ones. The objective of the proposed effort is to find plasma regimes where the thermal electromagnetic noise does not exceed that in solid-state devices and where ohmic losses are low. The key concept is to utilize plasmas generated by repetitive short pulses to sustain high electron density at low time-averaged electron temperature. If successfully demonstrated, the new concept could enhance fundamental understanding of electromagnetic properties of plasmas and enable novel practical devices.
