Abstract: A microwave oscillator with an M-type interdigital slow wave resonator structure is disclosed. In the above oscillator, the anode has top, middle and bottom resonance discs. The top disc has downward extending vanes and defines an upper resonance chamber, while the bottom disc has upward extending vanes and defines a lower resonance chamber. The upper and lower resonance chambers is separated from each other by a middle resonance disc that has upward and downward extending vanes. An emitter is placed between the filament and the anode and emits thermions into the actuating space when it is heated by the filament. The upward extending vanes of the middle disc engage with the vanes of the top disc in the type of interdigital engagement like clasped hands. The downward extending vanes of the middle disc engage with the vanes of the bottom disc in the same manner.