Figure 1: Parts of slip ring unit
In a radar with a rotating antenna, not only the transmission energy must be transmitted from the fixed part (stator) of the turntable to the rotating part (rotor) using an RF rotating joint but also supply voltages and a large number of switching and control signals as well as data lines.
The picture shows parts of a slip ring unit of the weather radar Meteor 1500 from Gematronik. In a carrier cast out of plastic (made of insulating material), ring-shaped contact surfaces are embedded, on which a spring contact allows the current to flow during rotation. The surfaces are gold plated. In order to work with as little wear as possible, the contact spring presses as weakly as possible, but still sufficiently strong for a safe current flow against the rotating ring-shaped contact surface.
In the example shown, the contact spring consists of a thin hard gold-plated steel wire soldered into a carrier circuit board. If larger currents have to be transmitted, the contact spring consists of large-area carbon contacts. The abrasion of the carbon surfaces creates graphite dust which must be removed at regular intervals during maintenance cycles to prevent short circuits. Gold-plated contacts are maintenance-free.