Plasma cathodes can be used as electron sources in electric propulsion applications. Unlike hollow cathodes where a low work function insert material that needs to be heated to elevated temperatures is utilized for the electron emission, plasma cathodes do not need to be preheated, and could be switched on instantaneously. Recently, at Bogazici University Space Technologies Laboratory (BUSTLab), radio frequency (RF) plasma cathode devices for use as electron sources of plasma thrusters have been studied, manufactured and successfully tested. Introduction of a ferromagnetic core enhances the power transfer efficiency of the inductively coupled plasma (ICP). In this paper, we present the design, manufacture and tests of two prototype radio-frequency cathodes, one with a standard coil antenna and the other with Mn-Zn ferrite core, for use in space propulsion applications as an electron source. The extracted electron current, electron extraction cost and gas utilization factor for the developed plasma cathodes have been studied.