A S-band high power traveling wave tube for RADAR application

Abstract

Summary form given only: There is an increasing need for high power microwave sources. Among this class of sources, Traveling Wave Tube Amplifiers (TWTA) are attractive for high power applications such for radars and long range satellite communications systems. Several important factors influence the performance of TWTs. Among them are: a suitable Slow Wave Structure (SWS) within the tube, beam focusing, attenuation, electron beam to wave interaction, collector module, and cooling efficiency. At the meeting several factors will be considered in addressing the issues relating to reflection, interaction with electron beam, support layout etc. The typical challenges are: . Reflection of the backward wave is a major concern as it diminishes forward gain greatly. A good attenuator circuit is also necessary to absorb reflections due to impedance mismatches and space charge waves. . Interaction with the relativistic electron beam is crucial for high power TWTs. Specifically, high phase velocity in the RF wave worsens the coupling. As a result, a longer tube is needed for stronger interaction, implying difficulty with its miniaturization. . A good support of the slow wave structure is also needed inside the TWT. Traditionally, dielectric materials were used to slow down waves and provide non-conducting contact between the SWS and waveguide wall. But dielectrics also scale down the electron beam velocity, implying smaller saturated powers. Thus, a suitable support layout is needed to also maintain high power characteristics. In this work, we will present a practical design of an S-band high power Traveling Wave Tube for radar applications. This is done by using a Slow Wave Structure (SWS) inside the TWT that has a `Curved Ring-Bar' to achieve efficient interaction with the electron beam. The designed SWS is capable of coupling with the electron beam even when its velocity is as large as 0.82c. Importantly, the interaction impedance of the structure is nearly flat across the entire S-band with minimum value of 48Ω. However, the structure possesses features which may generate large space charge forces between the electron beam and the metal strips of the SWS. To overcome this issue, a modified design is presented and simulations will be presented using a PIC code to demonstrate the coupling of the electron beam with the generated RF wave. Issues relating to the intense spacecharge waves, power suppression and beam focusing will be addressed as well.