A coupled-cavity TWT operating in the inverted slot mode

A coupled-cavity TWT has been designed to operate in the inverted slot mode (ISM), as a lower-cost alternative to a standard coupled-cavity tube. An ISM circuit is less expensive to fabricate; it needs no lossy resonators for oscillation suppression due to vanishing interaction impedance at the upper cutoff frequency. The cavity size is also significantly smaller. This permits forming the cylindrical cavity wall by the magnetic ferrule hole in a PPM focused device. The cavity partition walls (webs) can then be made of copper to enhance the thermal capability of the circuit. A PPM focused ISM tube demonstrated 20 kW of peak power over the band 5.25-5.75 GHz. Its RF performance was generally comparable to that of a standard coupled-cavity design. For equivalent gain the ISM circuit needs to be longer (by 30-35 percent), but it would generally weigh less and have higher average power capability.