GaAs and GaN are compound semiconductors commonly used to make RF power amplifiers. GaAs is widely used for microwave applications up to 30 GHz, such as in cell phones and cable TV systems, but is limited to around 5W of power. GaN has higher power density, allowing power levels of tens of watts from individual amplifiers and hundreds to thousands of watts from combined configurations. GaN is increasingly replacing GaAs and traveling wave tubes for military radar and satellite applications. Both materials are used with various transistor types optimized for RF amplification.