Several novel field emission cathodes are constructed by attaching a variety of materials to a steel substrate using multiple methods of bonding. These cathodes are tested using a pulsed relativistic (350–550 kV) vircator in a space charge limited operating regime. The viability of these cathodes as advanced or alternative components in high power microwave systems is evaluated. The currents measured from the cathodes are compared to values predicted from a 3D space charge limited flow model. The performance of the cathode is determined by how the current deviates from the model, as well as the consistency and durability.