Microwave plasma varactors

A low-loss, low-noise plasma varactor has been developed. This is a variable microwave reactance produced by means of a low pressure, highly efficient gas discharge. This device compares favorably with ferrite or semiconductor devices as far as rf losses and average rf power handling capability are concerned. A low-loss phase shifter has been developed using these plasma varactors. Overall rf losses (including the reflection, circuit and plasma losses) smaller than 0.5 db have been obtained over a bandwidth of 12% at X-band frequencies for continuously variable phase angles well in excess of 360°. An average power handling capability in excess of 200W has been obtained from this device. While the original work was performed at X-band, extrapolations of the results indicate that 1he substantially improved performances (with an excess noise temperature smaller than 100°K and with a multi-kilowatt rf average power handling capability) will be possible throughout the whole microwave, frequency range.