Abstract: A test waveguide (33) for evaluating the performance of microwave probe assemblies (1, 13) and their associated analysis equipment is mounted on a stand (56). The test waveguide (33) includes geometry that is similar to that found on the test cell assembly (2) used during commercial production activities. The test waveguide (33) includes an unsealed interior space (41) that remains accessible while the probe assemblies (1, 13) are fastened to the test waveguide. One or more reference blocks (59) are formed having known characteristics that permit calibration and evaluation of the probe assemblies and their associated analysis equipment.