Srivastava V, Ghosh TK, Sharma RK, Sinha AK, Singh VVP, Raju RS, Alaria MK, Imtiaz SM, Kiran V* Microwave Tubes Area, Central Electronics Engineering Research Institute Pilani (Raj.)-333 031 Fax: 01596-242294, phone: 01596-252228, e-mail: vs@ceeri.ernet.in *Microwave Tubes Division, Bharat Electronics Limited, Bangalore