In this study, a broadband power amplifier prototype which has a very fine flat gain level and high efficiency in the wide operating bandwidth is designed. The designed prototype operates in S-Band over the 3.4 GHz - 4.0 GHz frequency range with a nearly 12.7 dB power gain and delivers approximately 45.7 dBm or 37 Watts power to the 50 Ohm load. In the wide operation bandwidth, the power added efficiency of the device is more than 70% which is a sufficiently high value for Class-AB power amplifier operation. For the designing of prototype, 35W DC-6 GHz GaN HEMT device CGH40035F of Cree Wolfspeed Company is preferred and utilized. In the course of the design, a novel procedure is followed and sufficiently successful results are obtained. For the first stage, appropriate source and load impedances are properly determined regarding delivered power and efficiency levels. In the second stage, lumped element prototype is generated employing impedance based real frequency single matching technique. Finally, some of the lumped elements are replaced with their distributed equivalents to form up the design and performance of the overall mixed-element system is re-optimized for further fine results.