Microwave rotary connectors are essential components used to transmit high-frequency signals between a stationary platform and a rotating one. These devices enable continuous RF signal transmission between structures that have relative rotational motion, ensuring uninterrupted communication. Their applications span across various fields such as air traffic control radar, anti-missile systems, medical equipment, satellite communications, and camera systems. By eliminating the risk of cable tangling due to 360-degree rotation, they significantly enhance system reliability.
Depending on the frequency range required for signal transmission, microwave rotary connectors can be categorized into three main types: (1) Contact-type slip rings, which typically operate in the 0–120 MHz range; (2) Coaxial contact rotary connectors, capable of handling frequencies up to 0–50 GHz; and (3) Non-contact rotary connectors, which can use either coaxial or waveguide technology. These non-contact designs offer long service life and a wide transmission bandwidth, usually covering about 20% of their maximum operating frequency.
Current market demands emphasize miniaturization, low insertion loss, excellent VSWR (Voltage Standing Wave Ratio), minimal vibration during rotation, and high channel isolation within the operational frequency range. To meet these requirements, advanced design techniques and materials are employed.
In RF coaxial theory, common characteristic impedances are 50Ω and 75Ω. For a 50Ω connector using an air dielectric, the ratio of the outer conductor's inner diameter (D) to the inner conductor's outer diameter (d) is approximately 2.3. When PTFE is used as the dielectric material with a relative permittivity of 2.04, this ratio increases to around 3.29. Most RF coaxial connectors use copper alloys for the inner conductor and steel or brass for the outer conductor, with air or PTFE as the dielectric medium.
The design process involves several key steps: selecting appropriate inner and outer conductor dimensions based on the intended frequency, designing the groove structure, choosing input/output interfaces like SMA type, performing full-scale simulations using tools like HFSS or MWS, analyzing power capacity, manufacturing, testing, and conducting environmental and reliability tests.
A practical example of a microwave rotary connector was designed with a small size, simple structure, and a minimum operating frequency of 10 GHz. The SMA connector was chosen due to its international standardization and widespread use. The cutoff frequency of the SMA connector was calculated, and the design ensured minimal reflection by maintaining consistent inner conductor dimensions. The final structure included an SMA outer conductor, PTFE dielectric, and a miniature bearing to support rotation.
Testing results showed that the connector performed well across a 0–15 GHz range, with a VSWR of ≤1.25, insertion loss ≤0.5 dB, and peak power capability of 1000 W. Additional considerations during the design phase included precise dimensional tolerances, gold plating for better conductivity and wear resistance, and optimized groove geometry to reduce signal distortion.
This microwave rotary connector offers a compact, cost-effective solution suitable for integration with other systems, especially where low-speed rotation is required. Its design highlights the importance of material selection, precision manufacturing, and careful attention to electromagnetic performance to ensure reliable operation in real-world applications.
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