A solid-state microwave generator for applying energy to a load disposed in a cavity is provided. The microwave generator comprises an oscillator, a preamplifier coupled to the oscillator, a power amplifier coupled to the preamplifier; a radiating element coupled to the power amplifier and in communication with the cavity; and a passive, microstrip bandpass filter with a predetermined passband in the microwave region of the electromagnetic spectrum connected in a line between the oscillator and the power amplifier. The output of the passive, microstrip bandpass filter is connected to an input of the power amplifier to limit the energy transmitted by the radiating element into the cavity at frequencies outside of the passband.