A novel cylindrical $TE2,1$ mode converter

A novel, compact arrangement for Ka-band mode couplers, which convert a rectangular waveguide $TE1,0$ to cylindrical waveguide $TE2,1$ mode, has been designed, constructed, and tested. The design features a set of longitudinal slots, positioned in regions of negligible current flow for the $TE2,1$ mode, allowing its propagation to be preferentially favored, by suppression of the fundamental $TE1,1$ mode. Numerical simulations and experimental measurements display good agreement, showing transmission of the intended $TE2,1$ mode at levels of better than −5 dB, from a frequency of $∼37.5$ to 41 GHz. Subsequent farfield measurements confirm the presence of the $TE2,1$ mode, demonstrating good agreement when compared with analytical expectations. Such a device would be an ideal candidate for an application where mode purity, bandwidth, and ease of construction are of primary importance and where the transmission efficiency is of limited concern.