Abstract: Characteristics of a two-layer patch microstrip antenna(MSA) for high power wide-band microwave radiation was studied. A new conical feeder was introduced to reduce lead inductance of conventional probe feeder. It increases antenna’s power capacity to hundred megawatt level and plays as a convertor between coaxial waveguide and dielectric resonator, which means less reflection at the port. The effect of dielectric substrate thickness and patch size on MSA’s bandwidth was analyzed based on electromagnetic simulation. Percentage bandwidth of 34.9% (voltage standing-wave ratio less than 3) was obtained after dimension optimization, the gain is above 6.5 dB over the whole band with the maximum of 8.3 dB at 310 MHz, and the ratio of far-zone radiation factor to input impulse voltage is 1.3 i