Advanced TWTAs for Space Communications

Advanced TWTAs have been developed for space communications that cover the down link bands centered at 12 GHz and 20 GHz. These state of the art amplifiers include M-type dispenser cathodes that provide high cathode loading and long life, and the velocity taper in the output helix circuit to improve efficiency and phase distortion. Power levels in excess of 50 watts in Ku band and 30 watts in K band have been demonstrated in amplifiers that combine advanced techniques with designs proven in several space programs including DSCS III, Landsat D and GEOSAT. Key design parameters and RF performance, as well as life test data using the M-type dispenser cathode, will be presented on several versions of these amplifiers. Further improvements in TWTA amplifiers at these higher frequencies will also be discussed and compared to the projected needs for space communications.