Claims
1. A reflector antenna comprising:
a dual-band waveguide feed (210; 810; 910) configured to receive an input signal in a first transmission mode, the input signal including a plurality of frequencies arranged into upper and lower frequency bands, and the waveguide feed including means for converting a transmission mode of the upper frequency band from a first transmission mode to a mixed transmission mode including the first transmission mode and a second transmission mode;
a reflector;
a splashplate (230; 830) configured to direct a beam emitted from an aperture (210a) of the waveguide feed to the reflector; and
a splashplate support (240; 840; 940) comprising a first engaging portion (240a; 840a; 940a) for engaging with the waveguide feed, a second engaging portion (240c; 840c, 840c) for engaging with the splashplate, and a supporting portion (240b; 840b; 940b) connecting the first engaging portion to the second engaging portion and arranged to define a space between the waveguide feed aperture and the splashplate.
2. The reflector antenna of claim 1, wherein the supporting portion is configured to be spaced apart from the aperture of the waveguide feed in a direction away from the splashplate, when the first engaging portion is engaged with the waveguide feed.
3. The reflector antenna of claim 1 or 2, wherein the supporting portion has a thickness less than or equal to substantially A/2, where A is a characteristic wavelength of the beam inside the supporting portion.
4. The reflector antenna of claim 3, wherein the characteristic wavelength is a wavelength corresponding to a centre frequency of a transmission band of the beam emitted from the aperture of the waveguide feed, or is an average wavelength of the beam, or i s a value between the average wavelength and the wavelength corresponding to the centre frequency.

5. The reflector antenna of any one of the preceding claims, wherein the supporting portion has a shape corresponding to a wavefront of the beam emitted from the waveguide feed after it has been reflected from the splashplate.
6. The reflector antenna of any one of the preceding claims, wherein the supporting portion is curved or elliptical in cross-section.
7. The reflector antenna of any one of the preceding claims, wherein the supporting portion is a substantially continuous wall.
8. The reflector antenna of any one of the preceding claims, wherein the first engaging portion is configured to engage with an outer surface of the waveguide feed.
9. The reflector antenna of any one of the preceding claims, wherein the splashplate support is formed of polytetrafluoroethylene PTFE.
10. The reflector antenna of any one of the preceding claims, wherein the means for converting the transmission mode is spaced apart from the aperture by a predetermined distance, such that for the upper band both the first and second transmission modes are substantially in phase at the aperture.
11. The reflector antenna of any one of the preceding claims, wherein the means for converting the transmission mode of the upper frequency band comprises a taper, one or more steps, or a profiled change in the internal diameter of the waveguide feed, and connects a section of a first diameter D1 to a section of a second diameter D 2, wherein the second diameter i s greater than the first diameter.
12. The reflector antenna of any one of the preceding claims, wherein the fir;st transmission mode is a TEn mode and the second transmission mode is a TMn mode.

13. The reflector antenna of any one of the preceding claims, wherein the waveguide feed is circular in cross-section, and wherein a diameter of the aperture is substantially one wavelength of a frequency in the lower frequency band.
14. The reflector antenna of any one of the preceding claims, wherein the waveguide feed is configured for use at Ka band frequencies.
15. A satellite comprising the reflector antenna of any one of the preceding claims.