Correlated fanbeam extruder
Antenna systems and methods of detecting RF signals received from a field of view (FOV) are presented, employing intersecting fan beam pluralities formed by associated columns or rows of antenna elements and cross-correlation of components of the received radiation from the fan beam pluralities. The intersecting fan beams pluralities form pencil-like beams persistently spanning the FOV as desired. Angle(s) of arrival and frequency channels of incident RF signals may be determined through power estimation, ranking and filtering, and/or frequency channelization techniques. Higher sensitivity beams may be cued to more accurately characterize the incident signals.
1. Method of detecting RF signals received from a field of view (FOV) using an array antenna having elements, said method comprising:
receiving radiation, at a receiver associated with each element of the array antenna, the radiation coming from the FOV using a first fan beam plurality and a second fan beam plurality intersecting the first fan beam plurality to form a multitude of pencil-like beams at intersections, each of the fan beams originating from an associated column or row of antenna elements of the array antenna and pointing to a different angle in the FOV from its associated column or row with respect to the other fan beams in its respective fan beam plurality;
cross-correlating, by a cross-correlator, signal power at the intersections of the received radiation from the first fan beam plurality and second fan beam plurality in the FOV to create correlated output power estimates; and
using a comparator to compare the correlated output power estimates to a threshold power in order to rank RF signals detected in the radiation.
2. The method of claim 1 , wherein intersecting portions of the first fan beam plurality and second fan beam plurality form a plurality of pencil beams persistently spanning the FOV.
3. The method of claim 2 , wherein the plurality of pencil beams are formed with the full angular resolution of the array antenna.
4. The method of claim 2 , wherein the first fan beam and the second fan beam are orthogonal.
5. The method of claim 1 , further comprising estimating from the cross-correlation an amount of signal power present at the intersections of the first and second fan beam pluralities from one or more incident signals.
6. The method of claim 5 , further comprising:
cueing the formation of one or more beams of higher sensitivity than the intersecting first and second fan beam pluralities with the determined angle(s) of arrival of said one or more incident signals; and
characterizing the one or more incident signals with the one or more higher sensitivity beams.
7. The method of claim 6 , wherein the one or more beams of higher sensitivity are formed by the array antenna.
8. The method of claim 6 , wherein cueing further comprises associating through at least one of ranking and filtering the estimates of incident signal power with a respective azimuth and elevation of each of the associated first and second fan beam pluralities intersections.
9. The method of claim 1 , further comprising:
eliminating prior to cross-correlation beams from the first fan beam plurality and second fan beam plurality containing power below a threshold power.
10. The method of claim 1 , further comprising:
prior to cross-correlation, channelizing the fan beams into frequency channels and selecting for cross-correlation the frequency channelized channels above a threshold power.
11. The method of claim 1 , further comprising:
prior to cross-correlation, applying a fast Fourier transform to the first and second fan beam pluralities, and selecting for cross-correlation frequencies with coefficients above a threshold; and
wherein the cross-correlation is performed in frequency space by multiplying like complex coefficients.
12. The method of claim 1 , wherein:
the FOV is hemispherical.
13. The method of claim 1 , wherein at least one fan beam of the first fan beam plurality or the second fan beam plurality has a peak angle distinct from that of the other fan beams in its respective plurality.
14. The method of claim 1 , wherein at least one of the first fan beam plurality and the second fan beam plurality comprises at least one fan beam formed from a subarray of multiple columns or of multiple rows, respectively.
15. The method of claim 1 , wherein cross-correlating further comprises:
initially determining whether intersecting portions of the first fan beam plurality and the second fan beam plurality indicates a potential incident signal;
channelizing each of the fan beams into multiple frequency channels; and
cross-correlating each like spectral band in order to identify in which the frequency channels signals are present.
16. Method of operating a digital beam-forming array antenna, comprising:
in a survey mode, determining a respective angle of arrival of at least one incident signal using a plurality of persistent full bandwidth beams of full angular resolution formed by cross-correlation in a FOV by the array antenna, wherein the at least one incident signal has a signal power above a threshold power level; and
in a full aperture focused mode, electronically steering one or more beams formed with the array antenna at the respective angle of arrival with a higher sensitivity than the persistent full bandwidth beams.
17. Method of claim 16 , further comprising, in the survey mode, determining a presence of the at least one incident signal above a threshold power level.
18. The method of claim 16 , wherein the array antenna comprises an orthogonal array antenna.
19. An apparatus for detecting RF signals received from a field of view (FOV), comprising:
an array antenna for receiving radiation from a field of view (FOV) comprised of a plurality of columns of array elements orthogonal to a plurality of rows of the array elements for forming at least a first fan beam plurality and a second fan beam plurality intersecting the first fan beam plurality, each of the fan beams formed from one or more associated column or row and pointing to a different angle from its associated one or more columns or rows with respect to the other fan beams in its respective fan beam plurality to form a multitude of pencil-like beams at intersections;
a receiver for cross-correlating components of said received radiation; and
a signal processing lane for processing the components in order to rank incident signals of interest.
20. The apparatus of claim 19 , further including a processor for measuring cross-correlation output at the intersection of the fan beam pluralities in order to determine an angle of arrival of one or more incident signals.
21. The apparatus of claim 19 , wherein the array antenna comprises an orthogonal array antenna.
22. The apparatus of claim 19 , wherein the signal processing lane applies a particular digital time delay for a specific beam direction being created.