**6. Conclusions**

We have demonstrated that one or two plasma tubes can be used to focus, spread, and steer antenna beams. We have also shown that we can simulate convex and concave plasma lenses by using cylindrical plasma tubes. Focusing by a plasma is useful because it can be used to increase the gain of an antenna, and to quickly reconfigure the beamwidth as needed without physically moving the antenna. With this technology, there is no need for phased arrays. Beam steering with a plasma allows tuning to different frequencies which is a difficult task for standard antennas. Our experimental results with 44 GHz showed a dramatic improvement in beam steering and focusing characteristics compared to beam focusing and steering at 24 GHz. The shorter wavelength compared to the spatial variation in plasma density over the radius of the plasma tube, the easier it is to steer and focus antenna beams. These results have been incorporated in a new smart plasma antenna design which appears in another paper.

Driving the plasma with short high-current pulses allows CW operation at higher frequencies with a minimum amount of ionization power and higher plasma densities. Circuits for pulse forming and voltage multiplication are presented. The maximum frequency that a plasma antenna can operate CW has previously been limited by the high DC current needed to ionize the plasma. We minimize the average ionization power and increase the plasma density by using fast current pulsing with a short duty cycle. The average current is much lower but the average plasma density remains high than in the DC mode.
