In modern RF interconnect applications, microwave rotary joints play a crucial role. Whether in aviation radar, medical equipment, or industrial automation and telecom control, microwave rotary joints are widely used. They enable efficient connectivity between fixed RF parts and rotating components without impacting coaxial cables or other flexible transmission lines. This article will give a detailed introduction to microwave rotary joints in terms of definition, types, and their importance in practical applications.
Microwave rotary joints are essential components for connecting static RF systems with rotating RF lines. These rotary joints are often used in applications requiring 360-degree rotation, such as air traffic control, image transmission, medical and industrial applications, and various radar systems. Due to the high-performance interconnection, high reliability, and long lifespan requirements of these applications, microwave rotary joints typically use materials and manufacturing processes that meet military or aerospace standards to enhance their robustness and reliability.
Microwave rotary joints can be divided into two main types: coaxial rotary joints and waveguide rotary joints.
Coaxial rotary joints: These joints come with coaxial connector interfaces, typically divided into fixed and movable ends. Some coaxial rotary joints are right-angle types, with the rotating part located between two bends, without a distinct fixed end. Additionally, certain models offer flange mounting or PCB through-hole mounting interfaces.
Waveguide rotary joints: These include coaxial-to-waveguide and waveguide-to-waveguide rotary joints. The interfaces of these joints can be rectangular or circular, but the rotating part's interior is always circular. Waveguide rotary joints are suitable for specific applications and can effectively limit signal frequencies within the waveguide band.
Compared to traditional flexible transmission lines, microwave rotary joints achieve higher performance and lower loss. In most flexible RF interconnections, bending results in phase, loss, or other performance degradation. However, microwave rotary joints are not affected by this; their rotating part can freely move along the rotational axis without altering the internal dimensions of the transmission line. This means that microwave rotary joints can maintain higher power levels and reduce signal transmission loss, especially in high-performance and high-quality phase-stable flexible coaxial cable assemblies.
Designing microwave rotary joints requires consideration of several crucial factors, including insertion loss, bandwidth, Voltage Standing Wave Ratio (VSWR), impedance, and transmission line type. These factors directly impact the performance and reliability of the rotary joints. Therefore, engineers must carefully assess the actual application requirements when selecting microwave rotary joints to ensure the best interconnection results.
In many applications requiring rotational functions, microwave rotary joints are indispensable components. For example, in rotating antenna systems, microwave rotary joints allow the signal chain's rotating part to connect with the fixed part, ensuring stable signal transmission. In missile guidance systems and other rotary radar applications, the lack of microwave rotary joints would hinder efficient signal transmission, thereby affecting the overall system performance.
Designing microwave rotary joints also involves various mechanical factors, including maximum rotational speed and the number of plugging cycles. The maximum rotational speed is usually expressed in revolutions per minute (RPM). Compared to standard coaxial and waveguide adapters, microwave rotary joints require consideration of more usage scenarios and parameters to ensure stable operation under extreme conditions.
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