Electron beam tubes including ceramic material for realizing rf chokes

A linear electron beam tube having a longitudinal axis, comprising:

• an input cavity which is substantially cylindrical about the longitudinal axis and including means for applying to said cavity a high frequency signal to be amplified;
• an electron gun arranged to produce an electron beam in a direction substantially parallel with the longitudinal axis;
• a vacuum envelope within which the electron gun is contained;
• means disposed along the electron beam for causing said electron beam and said high frequency signal to interact to produce an amplified high frequency signal;
• and
• an output cavity surrounding the electron beam downstream of the input cavity along the electron beam direction and from which said amplified high frequency signal is extracted;
• wherein said input cavity substantially surrounds said electron gun and comprises an inner body portion electrically connected to part of the electron gun and an outer body portion electrically insulated from said inner body portion, said inner body portion being maintained at a relatively high voltage compared to that of said outer body portion,
• the inner and outer body portions each include respective first and second metallic portions extending in the direction of the longitudinal axis, the first metallic portion of the inner body portion being substantially co-extensive with the first metallic portion of the outer body portion in a direction substantially parallel to the longitudinal axis with ceramic material being located between the first metallic portions to act as a first rf choke, and the second metallic portion of the inner body portion being substantially co-extensive with the second metallic portion of the outer body portion in a direction substantially parallel to the longitudinal axis with ceramic material being located between the second metallic portions to act as a second rf choke, and
• the first and second rf chokes are located outside said vacuum envelope.