A high power UHF crossed-field amplifier

A forward wave UHF reentrant beam crossed-field amplifier has been developed to deliver 250 kw pulse output over the 406 to 450 MHz range. This amplifier is dc operated and uses a cold secondary emission cathode. Amplification is initiated by the input RF drive pulse and is terminated by a voltage pulse applied to a control electrode, which eliminates the need for a high power pulse modulator. This represents the first application of the dc operating technique to UHF tubes. To adapt the amplifier to forced air cooling its geometry was inverted, with the cathode surrounding the anode. The heat sink for the anode is at the center of the amplifier and cooling air is forced through a simple and compact system of cooling fins. The inverted geometry also provides a significant increase in the available cathode area.