There are a few cases with RF interconnects that require the connection between stationary RF parts and parts that rotate about an axis. The most common example of this is aviation radar that rotates 360 degrees. There are also many circumstances where it may be advantageous from an operator’s usability, installation, troubleshooting, or maintenance to have a RF interconnect that is able to rotate without leading to flexure cycles in a coaxial cable assembly or other flexible transmission line. In these circumstances, RF coaxial rotary joints are the ideal components to connect between stationary parts and allow for partial or even complete 360 rotation about an axis.
Why are RF Rotary Joints Used?
Compared to other types of flexible transmission lines, RF rotary joints may allow for much higher performance and less loss during. For instance, most flexible RF interconnects are impacted by phase, loss, or other performance degradation while undergoing flexure. For RF rotary joints, there is no flexure, and the rotary portion of the joint is able to move along its rotational axis without changing internal dimensions of the transmission line. This can allow for higher power levels and less loss than planar transmission lines on flexible circuits (flex circuits) and even high-quality phase-stable flexible coaxial cable assemblies specifically designed to maintain high performance while being adjusted.
Key RF Rotary Joint Electrical Specifications & Features
- Frequency Range [Hz]
- VSWR
- Insertion loss [dB]
- Power handling, maximum [dB]
- Impedance [Ohms]
- Shielding rating [dB]
- Interface type/gender
- Rotational Variation to VSWR and insertion loss
- Speed of rotation
- Outer conductor material
- Dielectric material
- Dielectric withstand voltage [V]
- Inner conductor material
- Operating temperature range [degrees Celsius]
- Orientation/shape [inline, bend]
- Mating cycle rating
- Inter-mate capability
- Size
- Weight
What Types of RF Rotary Joints Are There?
RF Rotary joints are typically one of three types. There are coaxial RF rotary joints, coaxial to waveguide RF rotary joints, and waveguide to waveguide rotary joints. Coaxial RF rotary joints have coaxial connector interfaces and both ends with a stationary and moving end typically designated. Some coaxial RF rotary joints may have right angle sections and the rotary portion is in the middle of these two bends, making no distinct stationary end. Other of this type of rotary joint have flange mounted or PCB through hole mounted board interface portions, as opposed to a typical coaxial connector.
Coaxial to waveguide RF rotary joints have a coaxial connector side and a waveguide flange side. The only difference with these rotary joints and coaxial RF rotary joints is that the waveguide section will ultimately limit the frequency operation to the waveguide band. Thera are also RF rotary joints that have waveguide interfaces on both sides.