This exhibit is marked IOCV-118O243e and looks like the DET22 which is a physically small disc seal triode valve, with co-axial connections.
The DET22 planar valve evolved during WWII as an improved replacement for the CV90.
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.
The DET22 is rated at 600 MHz but its extended maximum frequency of 4 GHz made it a natural choice for microwave designs.
The anode is slightly different to the DET22 sample we have but the flat end mounts very close to the grid as with similar valves.
A closer view of the anode and grid. The fine wires of the grid are fixed to one side of a carrier that is soldered to the grid mounting ring.
The cathode side of the grid showing the square carrier and fine grid wires that appear to be welded to the edges.
The planar envelope is 15 mm in diameter and, overall is 60 mm tall.
References: Data-sheet & 1040. Type DET22 was first introduced in 1945. See also1945 adverts.