Our laboratory has developed a drone detection radar that involves a mechanical scanning antenna. Radar and antenna systems that have mechanical scanning require an additional component called a rotary joint (RJ). The purpose of RJ in scanning assemblies is to provide an uninterrupted link between the antenna and the transceiver. In our system, antenna and transceiver are linearly polarized and use TE10 mode along the rectangular waveguide section. TE10 modes are asymmetric in nature making them incompatible with the rotating motion of the antenna. An RJ is presented with back-to-back mode transitions using symmetric modes along the circular waveguide and contactless branch line joint. The mode used along the circular waveguide for symmetry purpose is TM01. An I-type linear RJ topology is selected due to lack of space along the lateral directions and system configuration. The problem of antenna matching while scanning was solved at 14.0-14.5 GHz at Ku-band using single-channel linear RJ.