Radar

Abstract

An antenna system (1) comprises a directional antenna (2) adapted to rotate through a range of directions in azimuth. It is responsive to radio-frequency (RF) signals received from directions within the range of directions in azimuth. A receiver (7) is arranged to receive the RF signals from the antenna within a signal frequency response band of the receiver and to provide a corresponding output for signal processing. A signal filter (11) is operable to block the output from the receiver when the frequency of the RF signal lies at a frequency within the signal frequency response band of the receiver and a detector unit (8) is arranged to apply the signal filter when the directional antenna is directed to a predetermined azimuth at which an interference source is located and to not apply the signal filter otherwise.

Claims

1. An antenna system comprising: a directional antenna adapted to rotate through a range of directions in azimuth and responsive to radio-frequency (RF) signals received from directions within said range of directions in azimuth; a receiver arranged to receive said RF signals from the antenna within a signal frequency response band of the receiver and to provide a corresponding output for signal processing; a signal filter operable to block a said output from the receiver when the frequency of the RF signal lies at a frequency within the signal frequency response band; and a controller arranged to apply said signal filter when the directional antenna is directed to a predetermined azimuth and to not apply the signal filter otherwise.

2. An antenna according to claim 1 in which the directional antenna is arranged to rotate periodically through 360 degrees and the controller is arranged to apply said signal filter periodically.

3. An antenna according to claim 2 in which with the controller is arranged to apply said signal filter with a periodicity corresponding to the rotation period of said directional antenna.

4. An antenna according to claim 1 in which said predetermined azimuth is a predetermined range of azimuth angles.

5. An antenna according to claim 1 in which said signal filter is a high-pass filter arranged to block said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

6. An antenna according to claim 1 in which with the controller is arranged to apply said signal filter with a periodicity corresponding to a rotation period of said directional antenna.

7. An antenna according to claim 6 in which said predetermined azimuth is a predetermined range of azimuth angles.

8. An antenna according to claim 6 in which said signal filter is a high-pass filter arranged to block said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

9. A method for controlling a directional antenna system, the method comprising: rotating a directional antenna through a range of directions in azimuth, the antenna responsive to radio-frequency (RF) signals received from directions within said range of directions in azimuth; receiving said RF signals from the antenna at a receiver responsive to radio-frequency (RF) signals within a signal frequency response band to provide a corresponding output for signal processing; and selectively blocking a said output from the receiver using a signal filter if the frequency of said RF signal lies at a frequency within said signal frequency response band; whereby the signal filter is applied if the directional antenna is directed to a predetermined azimuth and is not applied otherwise.

10. A method according to claim 9 including rotating the directional antenna periodically through 360 degrees applying said signal filter periodically.

11. A method according to claim 10 including applying said signal filter with a periodicity corresponding to the rotation period of said directional antenna.

12. A method according to claim 11 in which said signal filter is a high-pass filter, and therewith blocking said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

13. A method according to claim 10 in which said predetermined azimuth is a predetermined range of azimuth angles.

14. A method according to claim 13 in which said signal filter is a high-pass filter, and therewith blocking said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

15. A method according to claim 10 in which said signal filter is a high-pass filter, and therewith blocking said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

16. A method according to claim 9 in which said signal filter is a high-pass filter, and therewith blocking said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

17. A method according to claim 9 including applying said signal filter with a periodicity corresponding to a rotation period of said directional antenna.

18. A method according to claim 17 in which said signal filter is a high-pass filter, and therewith blocking said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

19. A method according to claim 9 in which said predetermined azimuth is a predetermined range of azimuth angles.

20. A method according to claim 9 in which said signal filter is a high-pass filter, and therewith blocking said output from the receiver when the frequency of said RF signal lies below a threshold frequency defined by the signal filter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary, but non-limiting embodiment of the invention shall now be described with reference to the drawings of which:

(2) FIG. 1 shows schematically a buffer region separating telecommunications and radar signal frequency bands;

(3) FIG. 2 graphically shows the spectral characteristic of a filter according to an embodiment of the invention;

(4) FIG. 3 graphically shows the azimuthal dependence of the filter state in use according to an embodiment of the invention;

(5) FIG. 4 schematically shows a radar apparatus according to an embodiment of the invention.

(6) In the drawings, like items are assigned like reference symbols.

DETAILED DESCRIPTION

(7) FIG. 4 shows a schematic representation of a radar apparatus (1) comprising a directional antenna (2) arranged to be rotated in azimuth at a desired uniform rate (as shown by arrows). The antenna is arranged to form an antenna main beam (3) having an angular spread of Δθ degrees in azimuth. A telecommunications tower (4) radiates telecommunications signals having frequencies in a telecommunications signal frequency band shown in FIG. 1. The radar apparatus is arranged to receive radar signals with signal frequencies within the S-band shown in FIG. 1.

(8) The radar apparatus has a duplexer unit (5) connected to a transmitter (6) arranged for generating radar signals having frequencies within the S-band, and is connected to a first receiver unit (7) arranged for receiving radar signals having frequencies within the S-band. The duplexer is also connected to a second receiver unit (15) arranged for receiving radar signals having frequencies outside the S-band and within a telecommunications signal frequency band shown in FIG. 1. The RF signal input to the second receiver is obtained from the signal transmission line connecting the output of the duplexer to the first receiver. In particular, a directional coupler (14) is connected to the signal transmission line in question and is arranged to extract a small percentage of the RF signal thereon for input to the second receiver unit. This is for the purposes of detection of the presence of RF signals outside the frequency response band of the first receiver.

(9) A detector unit (8) is arranged to receive the signals output from the second receiver unit (15) and therewith to detect the presence of received RF signals having a frequency lying within a signals having frequencies in the telecommunications signal frequency band shown in FIG. 1. Concurrently, the detector unit is arranged to receive the signals output from the first receiver unit (7) and therewith to determine a measure of interference within RF signals within the signal frequency response band. The measure of the degree of signal interference is determined by measuring the power of the received signal from the first receiver unit.

(10) The predetermined threshold is a predetermined signal power level threshold value above which, if received by the receiver (7) of the antenna system, will overload the receiver and cause it to operate/respond non-linearly to received RF signals—i.e. whereby the receiver output is not in direct/linear proportion to the received RF signal input power. The detector unit compares the measure of interference (signal power) with a predetermined threshold value (overload power level) and if the threshold is exceeded, the detector unit deems the interference levels to be unacceptable and generates a filter control signal.

(11) The detector unit has a first output (9) upon which it outputs the input RF signal it received from the receiver unit (7) unchanged, and a second output (10) which is the filter control signal, both for input to a high-pass filter unit (11). The filter unit is responsive to the filter control signal to apply a frequency high-pass signal blocking filter to the receiver output signal (9) received by the filter unit (11), and to not apply the filter when the filter control signal is otherwise absent.

(12) The filter unit is arranged to apply the frequency filter during an azimuth range of width Δθ corresponding to the beam width of the antenna beam, centred on a frequency θ.sub.0 corresponding to the azimuth of the directional antenna (2) when the antenna beam (3) is centred upon the detected azimuth of the interfering telecommunications signals—namely, the telecommunications tower (4). An azimuth signal (13) is transmitted continuously from the azimuth control parts of the directional antenna to the detector unit and the detector unit is arranged to determine/correlate the azimuth angles occupied by the antenna when the detector unit detects telecommunications signals via the second receiver unit (15).

(13) FIG. 3 graphically shows the state of the filter unit, in response to filter control signals (10), as a function of azimuth angle, indicating the detected azimuth of the telecommunications tower and the antenna beam width. The filter is controlled to be selectively applied during antenna azimuth angles in the range Δθ centred upon azimuth θ.sub.0.

(14) FIG. 2 illustrates the spectral characteristic of the filter whereby a value 1.0 denotes full transmission and a value of 0.0 denotes no transmission (i.e. signal blocked). The filter is a high-pass filter which blocks the telecommunications band, and a lower part of the S-band. It can be seen that the narrow buffer zone separating the telecommunications signal frequency band from the radar S-band, is extended into the S-band. This extent may be an amount up to about ⅛.sup.th of the width of the S-band. Any further extension is likely to be detrimental to radar operations. It has been found that this extension is sufficient to amply remove the detrimental effects of interference from a neighbouring telecommunications band (e.g. 4G), but lesser extensions are also possible.

(15) The embodiments described above are presented for illustrative purposes and it is to be understood that variations, modifications and equivalents thereto such as would be readily apparent to the skilled person are encompassed within the scope of the invention.