METHOD OF PROVIDING TIME ALIGNMENT BETWEEN PHASED ARRAYS FOR COMBINED OPERATION

Abstract

A method of creating a timed array from a plurality of phased arrays is provided. The method comprises the steps of: phase steering each phased array to a desired pointing; applying processing to signals received from at least one of the phased arrays, wherein applying processing to the signals comprises applying, based on a reference, an adjustment to the signals from at least one of the phased arrays, such that the processed signals are substantially aligned in time with the reference; and combining the processed signals from each of the phased arrays; wherein the adjustment varies based at least in part on the desired pointing and the relative location of the phased arrays.

Claims

1. A method of creating a timed array from a plurality of phased arrays, the method comprising the steps of: phase steering each phased array to a desired pointing; applying processing to signals received from at least one of the phased arrays, wherein applying processing to the signals comprises applying, based on a reference, an adjustment to the signals from at least one of the phased arrays, such that the processed signals are substantially aligned in time with the reference; and combining the processed signals from each of the phased arrays; wherein the adjustment varies based at least in part on the desired pointing and the relative location of the phased arrays.

2. The method according to claim 1, wherein the adjustment comprises a time delay and a phase adjustment.

3. The method according to claim 1, wherein the adjustments in time and or phase applied to each of the phased arrays are obtained from the processing of signal received from the phased arrays.

4. The method according to claim 1, wherein the phased arrays are contiguous.

5. The method according to claim 1, wherein the phased arrays are distributed.

6. The method according to claim 1, wherein the step of applying processing to signals requires no a priori knowledge of the temporal difference between the signals received from each of the phased arrays.

7. The method according to claim 1, wherein the step of applying processing includes correlating the information within each signal to the information in the each of the signals from each of the plurality of phased arrays.

8. The method according to claim 1, wherein the step of applying processing includes correlating to a predefined code embedded in each signal.

9. The method according to any one of the preceding claim 1, wherein the time alignment is achieved by digital processing.

10. The method according to claim 9, wherein the signals from each of the phased arrays are formed into a series of digital samples.

11. The method according to claim 10, wherein the digital processing includes representing each of the signals from each phased array as a uniform series of digital samples which can be delayed by a predetermined number of samples with respect to one another, or with respect to the reference.

12. A method of transmitting from a timed array created in accordance with the method of claim 1, wherein the time and phase delays applied to each of the phased arrays are obtained from the processing of signal received from the phased arrays.

Description

[0025] The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0026] FIG. 1 shows a received signal on a distributed aperture; and

[0027] FIG. 2 shows a transmitted signal from a distributed aperture.

[0028] FIG. 1 shows a wave front W incident on two phased arrays 10 forming a distributed aperture 11. It will be appreciated that there may be more phased arrays 10 forming the distributed aperture, but only two are illustrated in order to simplify the illustration of the concept. It will also be appreciated that although the two phased arrays 10 are illustrated as spatially separated entities, they could be adjacent to one another in which case the distance L is the centre to centre distance. Alternatively, the arrays 10 could be adjacent, but angled relative to one another. This is applicable to applications where the arrays are positioned on the outer surface of a complex object such as a yacht, cruise ship, plane or tank. There may be relative movement between the phased arrays 10 and the source of the wave front W received. The wave front W may be received from a geostationary satellite by a moving object, such as a yacht, cruise ship, plane or tank. Alternatively, the phased arrays 10 may be provided on a building or land mass, but be configured to receive data from LEO satellites which move relative to the earth's surface. In each application there is relative movement between the signal source and the phased array receiving the wave front W.

[0029] The wave front W comprises a series of symbols 20, in the illustrated example four symbols 20 are shown. These symbols 20 are superposed on a carrier 30, which is illustrated as the sinusoidal waveform that underlies the symbols 20. In this example the symbols are provided at a frequency of 100 MHz or higher and the carrier frequency is in the region of 14 GHz.

[0030] The phased arrays 10 sample the incoming wave front W. The sampling rate is typically between twice and four times the symbol rate. The sampling rate is therefore between 250 MHz and 500 MHz. The data from the sampling is then converted from analogue to digital within the phased array 10 and then forwarded to a central processing location 40.

[0031] The effect of the distance L between the phased arrays 10 is smearing of the signal. As the phased array 10 on the left of the illustration receives symbol 1, the phased array 10 on the right of the illustration has already received symbols 1, 2 and 3 and is receiving symbol 4.

[0032] The data received from the phased arrays 10 at the central processing location 40 is illustrated graphically at 45. This shows the overlaying of four distinct inputs, smeared in time (horizontal axis) as a result of the spatial separation of the phased arrays 10 from which the data has been received.

[0033] In some embodiments the central processing location 40 includes a sampling clock which is distributed back to each of the phased arrays 10 in order to enable the different phased arrays to synchronise their sampling of the received data.

[0034] In some embodiments, the timing of the sampling is derived from a clock signal that is received from outside the system. For example, a GPS clock signal, accessible to all phased arrays 10 can be used to provide a clock signal to which each phased array 10 can synchronise its sampling.

[0035] The alignment of the received signals takes place in the central processing location 40 in two steps. Firstly, there is a coarse, or symbol level, alignment. This is achieved through providing a time delay 50 to the outputs from one or more of the phased arrays. In some embodiments, the output from one of the phased arrays is unchanged and all of the outputs from the other phased arrays are time delayed to match the first output. In some embodiments, the output of each of the phased arrays is brought into line with a consensus signal which is obtained as a calculation of the average of all of the outputs.

[0036] Once this has been completed, the phase is aligned to fine tune the alignment between the signals received from each of the phased arrays 10 by the application of a phase delay 60 to at least the output from one of the phased arrays. The phase of the output from one or more of the phased arrays is altered until the signals from the respective phased arrays constructively interfere to provide the maximum amplitude of combined signal. This combined signal can then be output from the central processing location 40 to a modem 70. The modem may be L-band or digital.

[0037] In an alternative embodiment, the sampled data is transferred directly to the central processing location 40 and the analogue to digital conversion is carried out centrally. Although this embodiment requires only a central analogue to digital converter, there is a risk of signal degradation in the data transfer from the phased arrays 10 to the central processing location 40.

[0038] FIG. 2 shows a wave front W emanating from two phased arrays 10 forming a distributed aperture 11. The data 95 from the received wave front W shown in FIG. 1 informs the selection of time delay applied in the central processing location 40. The phase delay 90 is applied locally at each phased array 10 in order to create a fully synchronised signal for transmission.