The DET22 is a physically small disc seal triode valve, with co-axial connections. The heater and cathode are opposite the main envelope and the emitting surface is a flat topped thimble. The grid has a circular connection to the flat internal metal mesh. The anode is copper and has a flat surface facing the grid and positioned very close to it.
A grounded grid configuration would allow for a two cavity mechanical design.
This valve is rated at 600 MHz but its extended maximum frequency of 4 GHz made it a natural choice for microwave designs.
The planar envelope is 15 mm in diameter and, overall is 60 mm tall.