Dual-band polariser

A system comprising

• a first part comprising first and second propagation paths configured to selectively propagate signals of a first frequency with either a first polarisation state or a second polarisation state, the first part being rotatable by 180 degrees between a first feed position in which the first propagation path is disposed within a first signal path and a second feed position in which the second propagation path is disposed within the first signal path, and wherein the first part is configured to allow propagation of signals in a second signal path in either the first or second feed positions;
• a transition part rotatable by 90 degrees between first and second transition positions, wherein the transition part is configured to selectively propagate signals of a second frequency along the second signal path with the first polarisation state when in the first transition position and with the second polarisation state when in the second transition position, wherein the transition part is configured to allow propagation of signals in the first signal path in either the first or second transition positions;
• a rotator part rotatable by 135 degrees between first and second rotator positions, the rotator part being configured to orientate the polarisation of signals in the second signal path in order to couple the second signal path to an interface, wherein the rotator part is configured to allow propagation of signals in the first signal path in either the first or second rotator positions,
• wherein the first part, transition part and rotator part are coaxial and wherein the second signal path is oriented along an axial path and the first signal path is offset from the axial path;
• a first radio unit configured to transmit and/or receive microwave signals at the first frequency;
• a second radio unit configured to transmit and/or receive microwave signals at the second frequency different to the first frequency;
• and
• a waveguide element operable to couple the second radio unit to the second signal path via the interface, and the first signal path to the first radio unit via a further interface.

A communications tower comprising:

• a first part comprising first and second propagation paths configured to selectively propagate signals of a first frequency with either a first polarisation state or a second polarisation state, the first part being rotatable by 180 degrees between a first feed position in which the first propagation path is disposed within a first signal path and a second feed position in which the second propagation path is disposed within the first signal path, and wherein the first part is configured to allow propagation of signals in a second signal path in either the first or second feed positions;
• a transition part rotatable by 90 degrees between first and second transition positions, wherein the transition part is configured to selectively propagate signals of a second frequency along the second signal path with the first polarisation state when in the first transition position and with the second polarisation state when in the second transition position, wherein the transition part is configured to allow propagation of signals in the first signal path in either the first or second transition positions;
• a rotator part rotatable by 135 degrees between first and second rotator positions, the rotator part being configured to orientate the polarisation of signals in the second signal path in order to couple the second signal path to an interface, wherein the rotator part is configured to allow propagation of signals in the first signal path in either the first or second rotator positions,
• wherein the first part, transition part and rotator part are coaxial and wherein the second signal path is oriented along an axial path and the first signal path is offset from the axial path;
• a first radio unit configured to transmit and/or receive microwave signals at the first frequency;
• a second radio unit configured to transmit and/or receive microwave signals at the second frequency different to the first frequency;
• and
• a waveguide element operable to couple the second radio unit to the second signal path via the interface, and the first signal path to the first radio unit via a further interface.