Tests of an electron gun based on diode acceleration followed by a two-cell RF cavity at 1.5 GHz are being
performed at PSI. The diode consists of a photocathode / anode assembly and is driven by a voltage pulse of 500 kV maximum in 200 ns FWHM. The diode configuration allows various types of cathode geometries including hollow cathode with field emitter array (FEA) inserts. In addition the diode assembly gives full control of the position, direction and size of the electron beam at the RF cavity entrance plane. Comparisons between simulations and measurements are presented for the case of a simplified elliptical photocathode geometry. First tests with a specially designed hollow cathode reveal a beam emittance below 0.5 mm.mrad for 10 pC charge.