A coupler provides a high speed datalink between rotating parts and comprises a circular channel, enclosing a hollow-cylindric volume, and at least two antennas. The circular channel is made of electrically conductive material and includes an inner ring, an outer ring rotatable against the inner ring, and two sidewalls on the sides of the rings. An inner antenna is mechanically coupled to the inner ring and an outer antenna is mechanically coupled to the outer ring. The antennas are configured to establish a microwave signal connection between them based on multiple reflections of an electromagnetic wave at the rings.

A filter structure has a frame carrying a filter compartment that holds first and second waveguide filters (F.sub.1H, F.sub.2H; F.sub.1L, F.sub.2L). The filter compartment is rotatable a predetermined angle around a rotation axis (AV) relative to the frame so as to either engage the first waveguide filter (F.sub.1H, F.sub.2H) or the second waveguide filter (F.sub.1L, F.sub.2L) in a waveguide conduit, thus rendering the waveguide conduit adapted for forwarding radio-frequency signals at a higher band or a lower band respectively. Consequently, the filter structure is suitable for inclusion in a dual-band radio terminal for communication with spacecrafts via an antenna unit exchanging radio-frequency signals bidirectionally with the spacecrafts.