Without more information it is impossible to give yo a valid answer. An annotated picture would be great. But I bet only a handful of people know what (DE) might refer to.
Probably super-glued in place. Grab it with a pair of pliers and snap it out of there Like a dentist pulling a tooth.
There are no circular C-Band transmissions in my line of sight, 55.5W ~ 139W and like most folks here don't use a dielectric slab and have no knowledge of using one.