« News Centre

Secure Transmission of Digital Data in Rotating Applications

The advantages of RF rotary joints from SPINNER include their compact design, outstanding VSWR and low insertion loss, low deviations of transmission properties during the rotation and a high degree of isolation between the individual channels throughout the entire frequency range. The company also works in the field of contactless power transmission.

In the field of radar technology, the trend of installing active components directly on the antenna is continuing. This allows a drastic reduction of the cable weight and a higher degree of system efficiency. At the same time, more complex and demanding technical solutions demand higher transmission rates for digital data.

These trends are changing the technical design of rotary joints for radar applications. The conventional RF rotary joint with its modules for different frequency bands is being replaced by a version with different components, such as a high power slip ring for the power supply and signal path-ways for the uplink to the rotating part of the radar installation and for the downlink of the received signal. In addition, the RF amplifier that is now located on the rotating part of the radar antenna must be cooled using a special fluid.

All this new technology demands a special transmission path, which is implemented in the rotary joint. A variety of different types of technology can be used for this transmission path. The electrical signals from and to active antenna equipment are transmitted via the slip ring, through a multi-channel fibre optic rotary joint or using a contactless coupler.

Contactless couplers with Ethernet interface

Ethernet technology has now become the standard in many product fields and is used as standard protocol for data transmission in radar systems. For this reason, SPINNER has equipped its newly developed contactless coupler with an Ethernet interface.

In principle, the coupler can be designed in any size, even with a central inner bore. It supports gigabit Ethernet, even with large free inner diameters, while the possible transmittable data rate is quickly limited by the geometry of the slip ring. The module automatically recognises the Ethernet standard of the connected devices – 10 base-T (10Mbit/s), rapid Ethernet (100Mbit/s) or gigabit Ethernet (1Gbit/s) – and prepares for the transmission. The module itself does not act as a client, it is invisible for the bus communication.

Various diagnostic functions and a complex function control are integrated into the electronics. Every rotor is subjected to a “burn in” before delivery. The product is only released for delivery after the RFC2544 test is successfully completed. This guarantees a very high degree of reliability throughout the entire life span of the Ethernet rotor. Contactless couplers are also available for other data bus protocols, such as CAN-BUS. Due to its modular concept, two independently working data transfer modules can be operated for each unit. Contactless data transmission can also be combined wita contactless power transmission (DC/DC converter) 24V/24V. This transmission provides the rotating part of the data transfer module with power. The unit also produces additional power of more than 50 W for external customer applications, such as the provision of sensors.

Both contactless data transmision systems and the contactless power transmitters can be used for high-speed applications up to 3000 U/min, with a consistent technical performance that is not linked to the rotation speed.

Sophisticated optical concepts

Fibre optic single-channel or multi-channel rotary joints (FORJ) are always used if the centre of the axis can be used for data transmission. Typically higher data transmission rates are used. This can be the case if several phased-array signals are transmitted in radar devices that cannot tolerate error in the analogue-digital conversion (A/D). With the fibre optic multi-channel solutions by SPINNER, analogue and digital signals can be transmitted without contacting technology. The transmission of several optical channels demands a sophisticated optical concept, as several laser beams have to be transmitted through the FORJ. SPINNER uses a rotating dove prism here combined with an ultra-precise but very robust mechanism.

The manufacturing procedure has been constantly improved over the course of time. Thanks to the discrete collimator, SPINNER is now able to supply fibre optic multi-channel solutions to meet customer specifications from a single source.