Explosive field emission cathodes constitute an important class of cathodes for high power microwave tubes. These cathodes have the advantages of being light weight and the capability of operating cold. In the past, this class of cathodes suffered from large amounts of outgassing, nonuniform emission, and very high emittance. These effects tended to dominate the diode performance, masking effects due to the anode. However, a type of carbon cathode has enabled the role of the anode in the diode to be better determined. In this letter, we compare experimental results with simulated diode performance, allowing an estimate of the bounds on the secondary emission coefficient from the anode surface as well as the amount of neutral gas liberated from this surface. In general, secondary electrons and neutral atoms lead to plasma formation in high power microwave devices, which in turn deleteriously affect the tube performance. Hence, an estimate of such quantities for use in particle-in-cell codes can prove pivotal for accurate modeling of experimental devices. © 2003 American Institute of Physics.