An apparatus capable of generating high power microwave frequency pulses for use with an electrosurgical device. The apparatus may be used for coagulating or ablating biological tissue. The apparatus includes an amplifier line-up comprising: a microwave signal generator for generating microwave radiation； a modulator arranged to pulse the microwave radiation； and an amplifier module arranged to increase the power of pulses of microwave radiation. The amplifier module works by providing a set of amplifiers that exhibit a gain that is greater than the total loss experienced at the components that divide the input signal and then combine the output signals. For example, if each amplifier in the array has a gain of 10 dBm, it is viable to use conventional power splitters and combiners to obtain an output microwave signal with substantially higher power than is provided by conventional electrosurgical generators.
