Presents a design of a 1-MV, frequency-doubling, four-cavity gyroklystron. The input cavity is driven by a 17.5-GHz driver and operates in the transverse electric (TE)/sub 011/ mode at the fundamental cyclotron resonance, while the buncher, penultimate, and output cavities operate in the TE/sub 021/ mode at twice the signal frequency at the second cyclotron harmonic. The device exhibits about 40% efficiency and 40-dB gain at 1-MW power level with a fractional bandwidth exceeding 0.1%. The power-bandwidth product for this device is on the same order as that of Ka-band gyroklystrons without the frequency doubling feature.