Several gyrotrons currently under development have cavities that operate in rotating TEnm modeswith very high azimuthal indices m such as a rotating TE15,2 or TE22,2 circular waveguide mode. If n<< m as well, these modes are sometimes called whispering gallery modes. It is desirable to be able toproduce these modes at low power from the TEio mode in standard dominant-mode rectangularwaveguide so that components to be used within or in conjunction with these gyrotrons can be moreeasily tested. Recently we discussed the principles of operation of a device which can be used to generatesuch high azimuthal index modes using an azimuthal array of apertures in the circular waveguide .Other methods of generating WG modes have also been developed. One uses a helical multifoil , andanother uses a cylindrical input cavity within a coaxial cavity . The azimuthal aperture array methodhas the possible advantage that more than one different WG mode with the same azimuthal index, m,could be generated with the same device. Also, both senses of rotation and any degree of rotation,including a stationary mode, can be produced with one device for possible testing purposes.