A Bragg cavity simultaneously provides selective single-mode feedback and transport of the intense electron beam. This avoids the problem of the end mirrors used in the conventional laser, which tend to block the beam. The use of a Bragg cavity for cyclotron autoresonant masers (CARMs), a multimegawatt source of millimeter and submillimeter wavelength radiation, is addressed. An extension of the design to 100 GHz is presented. The mode competition of TE6.1, TE3.2, TE2.2, and TM, the unequal length of the Bragg reflector, and a wide parameter choice have been considered. Ohmic losses in high-frequency CARMs have also been taken into account; the ohmic Q is 1.88 × 104, and the Q-factor of a Bragg cavity with a reflectivity of 96% on one side is 3.59 × 103.