Design of high efficiency space TWTs

High efficiency space travelling wave tubes (TWT) are essentially required for defense coherent radars and for satellite communication systems as a high power, high gain microwave amplifier. High efficiency (more than 60%) and high linearity (phase shift less than 30°) are very important aspects of a space TWT. Since 1997, efforts have been made at CEERI (jointly with BEL, Bangalore) for the successful design and development of high efficiency TWTs for space applications. Two projects have been sponsored by ISRO, Bangalore. A C-band 60 W space TWT has been successfully designed and prototypes have been developed jointly with BEL. Desired RF and electrical specifications were achieved over an extended frequency range of 3.40 GHz to 4.20 GHz with an output power more than 60 W, large-signal gain more than 50 dB, overall efficiency more than 55%, AM/PM factor less than 4 degrees/dB, and harmonic components and intermodulation (I/M) components more than 12 dBc down. Agreements between the simulated and the experimental values of the AM/PM factor, I/M components and the second harmonic power were achieved well within 10%. ´Quality assurance´ (QA) of the C-band 60 W TWT has been initiated for space qualification. The design of a radiation-cooled Ku-band 140 W space TWT has recently been completed and the design has been transferred to BEL for further joint development.