Many attempts have been made to replace vacuum tube transmitters with solid state power amplifiers to produce watt-level output power required in millimeter-wave satellite communication system. In one case, the use of standard rectangular waveguide to combine powers from many medium size microstrip solid state amplifiers was investigated. Each microstrip amplifier used in the PA module was attached to the input and output tapered-slot antennas to couple powers from and into the waveguide. The completed module contained several microstrip amplifiers inserted in parallel inside the waveguide, and one such component built using an X-band waveguide demonstrated more than 40 Watts of output power [1]. These waveguide power amplifier modules, however, could suffer from oscillations because of the strong coupling between individual microstrip amplifiers. In other to increase amplifier stability and the isolation among amplifier elements, we propose a technique similar to the one used in Wilkinson power divider. Our X-band simulated model used two amplifier elements with their tapered-slot antennas tied together using a 130${ extohm}$ resistor. With a proper antenna design and a careful selection of the location for the stabilizing resistor, HFSS simulations showed reduced coupling between two amplifier elements from-6 to below-15dB across the full waveguide bandwidth. The proposed stabilizing circuitry had almost no effect on the amplifier gain and power and made the PA module more resistant to the failures of individual elements.