Solid state amplifiers can now be constructed to achieve output powers and performance that have only been achievable by traveling wave tube amplifiers (TWTAs) through the use of MMIC amplifiers. These new high efficiency power amplifiers are designed to incorporate an antipodal finline antenna array within a coaxial waveguide that is investigated at Ka Band. This white paper demonstrates demonstrate a 120 Watt power amplifier operating from 27 to 31 GHz through the coaxial waveguide combiner structure by combining 10 Watt GaN MMIC devices.