GB2250153A

GB2250153A - Discovering hovering helicopters

Info

Publication number: GB2250153A
Application number: GB8517270A
Authority: GB
Inventors: Dipl Ing Gerhard Foeller
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1984-09-24
Filing date: 1985-07-08
Publication date: 1992-05-27
Anticipated expiration: 2005-07-08
Also published as: GB2250153B

Abstract

A monopulse radar sensor with at least one pair of antenna lobes K4-K7 substantially improves the probability of discovery, by carrying out a stepped search process by alternate steering of the pair of antenna lobes, using mechanical and/or electronic means. Between search steps the instantaneous displacement of the flying object from the direction of the antenna lobe centre is calculated using integrating filters. The antennae of the radar sensor can be arranged on a common carrier together with a weapon. <IMAGE>

Description

METHODS OF AND SYSTEMS FOR DISCOVERING HOVERING HELICOPTERS: The invention relates to methods of and systems for discovering hovering helicopters, using a radar sensor.

In specific situations, e.g. in the military sector, the use of radar devices for the early discovery and recognition of helicopters is of growing importance. Recognition measures more sophisticated than those needed for the mere discovery of target objects, and which are adapted to analyse and classify target echoes and to distinguish them from other types of target echoes, and from ground clutter and street traffic are needed. It is already known to use radar devices for the active location and recognition of helicopters and to analyse the echo signals in different ways. Thus for example, trained radar observers can utilise the Doppler frequencies obtained from a radar device in order to identify different classes of target by acoustic Doppler analysis.The radar echo of a helicopter has various components produced by reflections from the airframe, the main rotor, the tail rotor, the feathering gear, etc.

The echo which originates from the air-frame of a hovering helicopter does not supply an analysable Doppler frequency and thus cannot be distinguished from fixed targets. At a very low speed the air-frame supplies a Doppler frequency which is so low that it can be compared with that of slowly moving ground vehicles and in the case of many radar devices, on account of a higher cut-off frequency being used in the moving target indication filter, such echoes may be suppressed in the radar receiver, together with those of fixed targets.

From the German OS 32 33 327, for the use of radar devices which operate in the higher frequency band it is known to investigate the Doppler frequency range below the cut-off frequency of the Doppler filter by means of a filter circuit consisting of narrow-band individual filters, in order to establish line signals of target echoes which exceed a predetermined threshold value. The output signals of all the other individual filters and the output signals of the Doppler filter are subjected to sum formation and are fed to a second threshold circuit for the target decision. The wide-band spectrum in the Doppler frequency range which is specific to each helicopter serves to distinguish echo signals from other objects, e.g. cars.

The Doppler frequency which arises from moving parts of a hovering helicopter during the target sweep time is produced most intensively by the concentrated rotor blade, which has a reflection cross-section of approximately 50 to 100m2 with a lobe dwell time of approximately lms and a return time such as 100ms. As the illumination times of pulse-Doppier radar devices are often very much shorter than the return time of the rotor blade lobe of the helicopter, the short echo of the rotor is only rarely detected. Therefore these radar devices are suitable for Doppler frequency echoes of rapidly moving parts of the feathering gear having relatively small cross-sections.

In modern types of helicopter the feathering gear is provided with a cladding so that the detection facilities are restricted to the weak sources of tail rotor and side lobe of the main rotor.

Rotating surveillance radar antennae therefore lead to very long data renewal times, and are hardly suitable for the recognition of the rotor blade echoes.

One object of the present invention is to improve upon the methods of discovery of helicopters and the apparatus used therefore, to allow them to be recognised in a more reliable manner In accordance with one aspect of the present invention there is provided a method of discovering hovering helicopters using a radar sensor, in which a monopulse radar sensor has an antenna system producing at least one pair of antenna lobes and is used to detect echo signals characteristic of helicopt ers in combination with a stepped sweep process, where the space tracking of the helicopter is effected by alternate steering of pairs of antenna lobes using mechanical and/or electronic means, in each case following the calculation of the instantaneous displacement of the target object from the direction of the antenna lobe centre.

Using a method of this kind it is possible to fully avoid the difficulties of recognising rotor blade echoes by the use of wide antenna lobes and long illumination times.

Advantageously, in accordance with a further aspect, a radar system may be provided for performing the proposed method, in which, for military use the antenna of the mono-pulse radar can be arranged together with a weapon on a common carrier in such manner that, taking into account the weapon lead, the antenna lobe centre coincides with the direction of fire. As a result of the stepped steering of the antenna arrangement during the sweep process the weapon is thus simultaneously vectored. The use of the radar sensor, e.g. on the turret of an armoured tank, results in a cost savable combination of search and tracking device.

The recognition of the target object must take place prior to the commencement of an assault combat, and is carried out by a detailed investigation of the received rotor echo signals.

The analysis can take place for example by checking the return time of the echo signals or by the use of integrating time fil ters.

The invention will now be described with reference to the drawing, which schematically illustrates the use of a radar sensor for the discovery and recognition of helicopters in combination with an armoured tank at the beginning and at the end of a search and vectoring process. The drawing shows an armoured tank 1 with a turret 2 and a weapon 3. To each side of the weapon 3, pairs of antenna groups, 4 and 5, 6 and 7 are arranged, permanently connected to the turret 2. The search and vectoring process is advantageously effected in four phases, at the end of which the turret, together with the antenna array and the weapon, are automatically aligned to a target.

In the first phase the horizon is investigated by electronically steering the slightly divergent antenna lobes of the antenna pairs 4, 5 and 6, 7. If a helicopter is discovered the target position is immediately calculated, for example in accordance with the amplitude monopulse method, and the presence of the helicopter is recognised. The sequence of this first phase is shown in detail in the left-hand section, Figure la of the drawing.

The investigation process is carried out using the radar sensor antenna pairs 4, 5 and 6, 7, which produce antenna lobes K4, K5 and K6, K7. The execution of the search process is not dependent upon the use of two or more separate pairs of antennae, as one pair of antennae is basically adequate. In Figure la and in the following table the first phase of the search and vectoring process is divided into five time sections. At the times tl and t2 an unsuccessful search is recorded. Here, with a normal turret position, the antenna lobes of the antennae are steered as a result of a switch-over. When the antennae are again switched over at the time t3, a target is detected via the antennae lobes K6 and K7 and the position thereof is calculated.

In this position of the antenna lobes K6 and K7, the detected target object is then recognised during the times t4 and t5.

As shown in Figure la, the position of the turret 2 remains unchanged during the entire search-vectoring process phase, tl to t5: Time Lobe Pair Activated Target Report Position t tl K4/K5 Search t2 K5/K6 t3 K6/K7 30 > t < 75 Detection t4 K6/K7 Identification t5 K6/K7 At time t6 in phase 2, with the result of the coarse measurement, the turret 2 is coarsely steered in the direction of the target object, as shown in Figure Ib. Then in phase 3, at the time t6, the target object is finely measured by comparing the amplitude of the antenna lobes K5 and K6. In the final phase of the vectoring process the measurement of phase 3 is taken into account by fine steering. Following the fine steering of the turret 2 a monitoring measurement can also be carried out.The vectoring phases include the steering of the turret are shown in the right-hand section of the drawing, Figure lb, the phase sequence being: T Coarse steering of turret t6 Measurement by amplitude comparison K5/K6 T Fine steering of turret The recognition of a detected target echo necessitates a suitable propagation of the echo signals in a receiver of the radar sensor. If the target is a helicopter whose rotor has an even number of vanes, then the echo signals of the rotor exhibit no phase modulation. In this case it is possible to dispense with the use of an elaborate quadrature receiver. For purposes of analysis it is sufficient to rectify the received high-frequency echo signals.

For the recognition of a helicopter, the constant return time of the rotor echo is determined. For this purpose a simple circuit arrangement is used to check whether the interval of time between three consecutive discoveries is equal, for which purpose the illumination time of the double lobe is extended twice, for example by an amount of 100 ms. In a more elaborate version for the recognition of helicopters integrating time filters can be used.

Claims

CLAIMS:

1. A method of discovering hovering helicopters using a radar sensor, in which a monopulse radar sensor has an antenna system producing at least one pair of antenna lobes and is used to detect echo signals characteristic of helicopters in combination with a stepped sweep process, where the space tracking of the helicopter is effected by alternate steering of pairs of antenna lobes using mechanical and/or electronic means, in each case following the calculation of the instantaneous displacement of the target object from the direction of the antenna lobe centre.

2. A method of discovering hovering helicopters as claimed in Claim 1, substantially as described with reference to Figures la and lb.

3. A radar system for the execution of the method claimed in Claim 1 or Claim 2, in which the radar sensor and a weapon are arranged on a common carrier.

4. A radar system as claimed in Claim 3, in which the antenna lobe centre coincides with the direction of fire, taking into account the weapon lead.

5. A radar system as claimed in Claim 3 or Claim 4, in which the antennae of the radar sensor are permanently connected to the turret of an armoured tank.

6. A radar system as claimed in any one of Claims 3 to 5, in which at least one pair of antennae is provided for an antenna lobe pivotable in azimuth and in elevation for determination of the target position.

7. A radar system as claimed in any one of Claims 3 to 6, in which the return time of the rotor echo signals is checked to recognise the presence of a helicopter.

8. A radar system as claimed in any one of Claims 3 to 7, in which integrating time filters are provided for recognising the presence of a helicopter.

9. A radar system as claimed in any one of Claims 3 to 8, substantially as described with reference to Figures la and lb.

9. A radar system as claimed in any one of Claims 3 to 8, in which the turret of an armoured tank, together with the combat weapon, is automatically controlled into the direction of the target in stepped fashion by electronic beam scanning of the antenna lobe in association with pivot movements of the turret.

10. A radar system as claimed in any one of Claims 3 to 9, in which electronic steering of the antenna lobe is carried out by phase control.

11. A radar system as claimed in any one of Claims 3 to 10, in which the steering of the antenna lobe is effected by switching over a plurality of rigidly attached pairs of antennae.

12. A radar system as claimed in any one of Claims 3 to 11, substantially as described with reference to Figures la and lb.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS.

1. A method of discovering hovering helicopters using a radar sensor, in which a monopulse radar sensor has an antenna system producing at least one pair of antenna lobes pivotable in azimuth and elevation for determination of the target position, and used to detect echo signals characteristic of helicopters, in particular to check the return time of the rotor echo signals, using integrating time filters for recognising the presence of the helicopter in combination with a stepped sweep process for tracking of the helicopter by alternate steering of the or each pair of antenna lobes using mechanical and/or elecontronic means, the calculation of the instantaneous displacement of the target object from the direction of the antenna lobe centre being effected after each step, before the subsequent step is commenced.

2. A method of discovering hovering helicopters as claimed in Claim 1, substantially as described with reference to Figures la and ib.

3. A radar system for the execution of the method claimed in Claim 1 or Claim 2, in which the radar sensor, antennae, means for determination of the target position, means to determine the return time of the rotor echo signals, and integrating time filters, are arranged on a common carrier together with a weapon.

6. A radar system as claimed in any one of Claims 3 to 5, in which the turret of an armoured tank, together with the combat weapon, is automatically controlled into the direction of the target in stepped fashion by electronic beam scanning of the antenna lobe centre in association with pivot movements of the turret.

7. A radar system as claimed in any one of Claims 3 to 6, in which antenna lobe electronic steering is carried out by phase control.

8. A radar system as claimed in any one of Claims 3 to 7, in which the antenna lobe steering is effected by switching over a plurality of rigidly attached pairs of antennae.