Antenna

1. A phased array antenna for providing a radiation pattern having at least one communication beam, the antenna comprising:

a plurality of antenna elements, wherein each antenna element will have an antenna element signal having a phase relationship and an amplitude relationship to the other element signals;

a digital signal processing arrangement for providing a digital beamforming network; and

an analogue beamforming network arranged for reducing exposure of the digital signal processing arrangement to an interfering signal, the analogue beamforming network being configured to apply analogue beamforming weights selected to generate a null in a radiation pattern in a direction corresponding to the interfering signal to signals received from said antenna elements, and the digital beamforming network being configured for applying digital beamforming weights for each of said at least one communication beam to signals received from said analogue beamforming network such that a composite radiation pattern of the antenna will provide said at least one communication beam.

2. A phased array antenna according to claim 1 , wherein said antenna elements are partitioned into a plurality of overlapping subarrays, each subarray comprising:

a subset of all the antenna elements, said analogue beamforming network being configured to allocate to elements of each subarray respective subarray beam-forming weights for creating said null and said digital beamforming network being configured for allocating to each subarray beamforming weights for said at least one communication beam so as to produce said at least one communication beam.

3. A phased array antenna according to claim 2 , wherein said analogue beam-forming network is configured for creating more than one null in a radiation pattern.

4. A phased array antenna according to claim 3 , wherein each subarray comprises more than two antenna elements.

5. A phased array antenna according to claim 2 , wherein each of a plurality of antenna elements will participate in a number of subarrays equal to the number of elements per subarray.

6. A phased array antenna according to claim 5 , wherein the analogue beamforming network comprises:

a number of output ports and the digital signal processor comprises a number of input ports, each subarray being coupled to an output port and each output port being coupled to a separate input port of the digital signal processor and wherein the number of output ports of the analogue beamforming network is equal to the number of antenna elements of the phased array antenna.

7. A phased array antenna according to claim 6 , wherein the analogue beamforming network is operable to apply, when no nulls are desired, beamforming weights to elements of each subarray such that each signal provided to an output port will be from a different single antenna element.

8. A phased array antenna according to claim 2 , wherein the digital beamforming network comprises:

at least one control point for each antenna element.

9. A phased array antenna according to claim 2 , wherein said analogue beamforming network comprises:

phase weighting and amplitude weighting means coupled to each antenna element for applying beamforming weights to signals from the antenna elements; and

a summing device for each subarray for summing the weighted signals.

10. A phased array antenna according to claim 2 , comprising:

analogue to digital conversion means between the analogue beamforming network and the digital beamforming network.

11. A phased array antenna according to claim 2 , comprising:

a plurality of frequency demultiplexers, each demultiplexer being configured to demultiplex an output of a subarray into a plurality of frequency channels and wherein the digital beamforming network comprises:

at least one digital beamformer for each of the plurality of frequency channels, each digital beamformer being coupled for receiving respective frequency channel signals from each subarray output and being arranged for applying a complex weight to each of said respective frequency channel signals and for summing the weighted channel signals to provide a channel output signal.

12. A phased array antenna according to claim 2 , wherein said antenna elements are arranged in two dimensions and each subarray extends in both dimensions.

13. A satellite communication system in combination with a phased array antenna according to claim 1 .

14. A method of operating a phased array antenna for providing at least one communication beam, said phased array antenna having a plurality of antenna elements, each antenna element having an antenna element signal having a phase relationship and an amplitude relationship to the other element signals, a digital signal processing arrangement providing a digital beamforming network, and an analogue beamforming network arranged to reduce exposure of the digital signal processing arrangement to an interfering signal, the method comprising:

allocating, in the analogue beamforming network, analogue beamforming weights to signals received from said antenna elements to generate a null in a direction corresponding to the interfering signal;

providing output signals from said analogue beamforming network to the digital beamforming network; and

allocating digital beamforming weights, in the digital beamforming network, for each of said at least one communication beams to said output signals of said analogue beamforming network such that a composite radiation pattern of the antenna provides said at least one communication beam.

15. A method according to claim 14 , comprising:

partitioning said antenna elements into a plurality of overlapping subarrays, each subarray having a subset of all the antenna elements;

wherein allocating beamforming weights to said signals received from said antenna elements includes allocating to elements of each subarray respective subarray weights;

wherein providing output signals from said analogue beamforming network includes summing weighted signals from elements of each subarray to provide an output signal for each subarray to the digital beamforming network; and

wherein allocating beamforming weights to said output signals includes allocating to each subarray respective beamforming weights for said at least one communication beam to provide said at least one communication beam.