Two field plate variants of AlGaN/GaN-HEMTs with and without source-connected field plate ("shield") were analyzed for the design of efficient High-Power-Amplifier MMICs operating at X-Band frequencies. This paper presents the design and realization of three dual-stage microstrip MMICs using different device variants for narrowband and broadband applications. Two narrowband HPAs, using GaN HEMTs with and without shield, achieve a maximum output power and PAE of 20 W and >39 %, respectively. A broadband amplifier containing GaN HEMTs without shield reaches a simulated output power beyond 12 W with >30 % PAE over 9-11 GHz.
