Multi-band radio-frequency (RF) antenna system

1. An apparatus comprising:

a primary reflector; and

a near-field feed arrangement comprising:

a multi-band waveguide feed comprising a first waveguide feed for a first frequency band and a second waveguide feed for a second frequency band separate to the first frequency band, wherein the first waveguide feed and the second waveguide feed are co-axial and have, respectively, a first aperture and a second aperture, and wherein an adjacent skirt extends outwardly from the second aperture; and

a splashplate located within the near-field of the first waveguide feed and located within the near field of the second waveguide feed, wherein the splashplate is configured as a feed for the primary reflector and defines a continuous surface that comprises a first portion comprising one or more concave surfaces and being configured as a feed for the first frequency band and a second portion comprising one or more concave surfaces and being configured as a feed for the second frequency band, and

wherein the first aperture is closer to the splashplate than the second aperture.

2. An apparatus as claimed in claim 1 , wherein the splashplate is separated from the first aperture of the first waveguide feed by a distance less than the Fraunhofer distance for the lowest frequency of the first frequency band, and the splashplate is separated from the second aperture of the second waveguide feed by a distance less than the Fraunhofer distance for the lowest frequency of the second frequency band.

3. An apparatus as claimed in claim 1 , wherein the splashplate is separated from the first aperture of the first waveguide feed by a distance less than twice a wavelength in free-space associated with a lowest frequency of the first frequency band, and the splashplate is separated from the second aperture of the second waveguide feed by a distance less than twice a wavelength in free-space associated with a lowest frequency of the second frequency band.

4. An apparatus as claimed in claim 1 wherein the first frequency band is higher than the second frequency band.

5. An apparatus as claimed in claim 1 configured to operate at least with a second frequency band less than 50 GHz and a first frequency band greater than 50 GHz.

6. An apparatus as claimed in claim 1 wherein the first portion is located within the near-field of the first waveguide feed and the second portion is located within the near field of the second waveguide feed.

7. An apparatus as claimed in claim 6 wherein the first portion is rotationally symmetric about a boresight axis and the second portion is rotationally symmetric about the boresight axis, wherein the one or more concave surfaces of the first portion are each rotationally symmetric about the boresight axis and wherein the one or more concave surfaces of the second portion are each rotationally symmetric about the boresight axis.

8. An apparatus as claimed in claim 1 wherein the multi-band waveguide feed is surrounded by the adjacent skirt that is rotationally symmetric about a boresight axis and comprises, when viewed in cross-section through the boresight axis, a tilted surface that recedes from the splashplate as it extends outwardly from the boresight axis.

9. An apparatus as claimed in claim 1 wherein the multi-band waveguide feed is surrounded by a second skirt that is peripheral and rotationally symmetric about a boresight axis.

10. An apparatus as claimed in claim 9 , wherein the peripheral skirt comprises a surface that:

(i) comprises one or more notches that are rotationally symmetric about the boresight axis and/or

(ii) is a tilted surface that extends inwardly towards the boresight axis as it recedes from the splashplate and/or

(iii) comprises added material for absorbing electromagnetic energy in at least the first and second frequency bands.

11. An apparatus as claimed in claim 1 wherein one or both of the first aperture and the second aperture are tapered horn apertures.

12. An apparatus as claimed in claim 1 wherein the first waveguide feed and the second waveguide feed are configured to have coincident phase centers for the first frequency band and the second frequency band.

13. An apparatus as claimed in claim 12 wherein the phase center for the first frequency band and the phase center for the second frequency band is a ring coincident with a focal ring of the primary reflector.

14. A network element comprising the apparatus as claimed in claim 1 , configured to use the apparatus for point to point wireless communication with another network element.

15. A cell tower of a cellular communications network comprising the apparatus as claimed in claim 1 , configured to use the apparatus for backhaul communication with a core network.