High frequency (HF) rotary joints (also called rotary couplings) typically have single channel or multichannel coaxial or hollow conductor couplings. In one configuration, an array transmits a wide-band electric signal between at least two components disposed for rotation relative to each other. The components are provided with coupling surfaces that are maintained at a largely constant distance from each other via the rotary movement. The space between the coupling surfaces is predominantly filled with a dielectric material.
In a coaxial, multi-channel design of a rotary joint, the rotor is mounted in the stator by means of rolling bearings such as thin ring bearings. These bearings, however, create the most mechanical and electrical or high frequency problems within the component. Because the rotor and rolling bearings consist of different materials (usually aluminum and steel), the temperature increases the friction or play due to the materials' different coefficients of thermal expansion. Increased friction regularly causes bearing damage, and increased play causes the electrical transmission properties to fluctuate. Additional disadvantages with these bearings are lubricant drainage at high temperatures, low resistance to corrosion of the roller bearings, and insufficient seal against the high frequency area, which is frequently kept at an elevated internal pressure by means of pre-dried air to improve the electric strength. HF rotary joints including rolling bearings, therefore, must undergo frequent expensive and time-consuming servicing, including a readjustment of the electrical properties after each servicing. During this process, the entire HF system to which the rotary joint belongs, such as a civil or military radar system, remains incapacitated.
It would be desirable to provide a rotary joint that addresses the above deficiencies, is long-lasting, and is substantially service-free.