Abstract: Improving the output power and power density of radar transmitter is an effective approach to increase the product of power-aperture of radar. By integrating LDMOS FETs and Si bipolar transistors with other microwave solid-state semiconductor power devices such as GaAs MMIC, a high power small-sized solid-state power amplifier is briefly introduced and developed. It is a valid method to improve output power and power density. The optimized design and simulation of LDMOS power FET circuits are detailedly discussed. To minimize the size a kind of matching circuit by combining microstrip distributed parameters with lumped parameters elements is provided.