DE4306920C2 - Radar device with synthetic aperture based on rotating antennas - Google Patents

Description

The invention relates to a radar device with a synthetic aperture based on rotating antennas according to the preamble of claim 1.

DE-PS 39 22 086 is such a device by the applicant became known in which at least one antenna for sending and receiving of radar pulses at the end of a rotating arm - for example one Helicopter rotor or a turnstile above the rotor axis is ordered. The received signals are demodulated and intermediate saves and then correlates with reference functions, which in Calculated depending on the lighting geometry of the radar device or be specified.

The parameters for this are the distance intervals to be measured, the Transmission frequency, the length of the rotating arm, the angle of rotation range the antenna from which signals are received, and the number of Transmitting pulses as well as the height of the rotating antenna above ground. The Cor The relation result is displayed, for example on a monitor.

Such a radar device can be used in real time in online operation and after corresponding modifications, for example alongside the landing aid and the obstacle warning also of target clarification and target pursuit to serve. The processor of this known device has several components and circuits on to do these diverse and complex arithmetic tasks to divide and thereby - as already mentioned - the real-time proximity or to ensure online operation. Here, the result for each of the distance interval always by correlating the received signal with receive a reference function valid for this distance interval The resolution of such a device in lateral and radial direction processing is - as explained in detail - by partially interconnecting coupled parameters determined.  

In the ROSAR signal processing carried out so far, one of the ide alen circular orbit with constant angular velocity. Now, however, it has been shown that the leaf tips during a Um deviations not to be underestimated by a regular circular path and because of the aerodynamic conditions perform stochastic movements that require an additional Doppler module cause the reception signal. However, since the reference function for a flat rotary motion with constant angular velocity net, the result of the correlation between the received signal and Reference function deteriorated or "smeared". The correlator result and thus the lateral resolution becomes worse if the rejection ideal circular orbit.

The invention has for its object a ROSAR device of the beginning to create the type mentioned, in which the above-mentioned defects elimi be renated and deviate from the ideal circular path for correction the rotor blade movements during a revolution in the reference signal be viewed.

This object is achieved by the measures outlined in claim 1 solves. An embodiment and further training is in the subclaim specified.

The following description is of exemplary embodiment le explained. The figures in the drawing supplement these explanations. It demonstrate:

Fig. 1 is a diagram of an illumination geometry to calculate the distance profile in side and plan view with a screwdown angle β with α = 0 °,

Fig. 2 is a diagram of an embodiment of the course of the difference α _p -α between the projected angle of rotation at the bottom α _p (t) and the angle of rotation in the rotor blade plane α for a rotor length L of 6 m and an angle of attack β as a variable, wherein the selected opening angle of the antenna in azimuth is 46 °,

Fig. 3 is a diagram according to Fig. 2 for the projection of the rotor blade length at the bottom L _p (t) as a function of the angle of incidence β for one revolution,

Fig. 4 is a diagram of FIG. 2 for the additional height .DELTA.H Term (t) as a function of the angle of incidence β for one revolution,

Fig. 5 is a diagram according to Fig. 2 for the result of the correlation S _OB (α _r), between the β by an angle β modulier th received signal and the computed for the planar rotary motion with con stant angular speed reference function for different values of as a function of angular displacement α _r ,

Fig. 6 is a circuit diagram of the processor for the ROSAR unit described in a schematic representation;

Fig. 7 is a circuit diagram of an embodiment of a processor for calculating the reference function due to the angle β by the modified illumination geometry.

Fig. 1 shows the lighting geometry for calculating the distance curve and thus the reference function with the angle of attack β. As an example of the deviation from the ideal circular path, a setting angle (pitch angle) β of the rotor blade tip during the passage of the rotor blade in the direction of the object, ie at α = 0 °, is assumed.

The projection of the angle of rotation on the ground α _p (t) is calculated using the projected rotor blade length L _PO at α = 0 °, ie with

L _PO = cos βL,

and α = ω _o · t as follows:

The projection L _p (t) of the rotor blade length L at an arbitrary angle of rotation α = ω _o · t is then

The height H (t) is calculated as a function of the angle of attack β as follows

H (t) = H _o + Lsin βcos ω _o t.

The quantity ΔH (t) = L · sin β · cos ω _o t represents an additional height term that changes with the angle of rotation α for a predetermined angle of attack β. With the help of these quantities, the oblique distance R _{is obtained} at α = 0 °:

Here R _{gn is} the distance between the center of the helicopter and the target for the respective distance interval with the number n at α = 0 °.

For the oblique distance R _A (t) between the rotor blade tip and an object on the ground, the expression can be found at any angle of rotation α

The projection of the angle of rotation α _p (t) and the rotor blade length L _p (t) on the floor, together with the additional height term ΔH (t), influences the lighting geometry.

Figs. 2 to 5 show an embodiment Meßaufzeichnungen for a given rotor length L of 6 m and a predetermined Anstell angle β as a variable. The dashed area applies to an opening angle of the antenna in azimuth γ = 46 °. In this case is shown in FIG 2 with α = ω _o t the course of the difference α _p -. Α between the projizier th angle of rotation at the bottom of α _p (t) and the rotation angle in the rotor blade plane α as a function of β for one revolution.

FIG. 3 illustrates the projection of the rotor blade length on the ground L _p (t) as a function of the angle of attack β for one revolution and FIG. 4 shows the additional altitude term ΔH (t) as a function of the angle of rotation β for one revolution.

The reference function S _RA (t), which takes the deviations from the ideal circular path into account, with the distance curve R _A (t) is:

S _RA (t) = I _RA (t) + jQ _RA (t)

with the in-phase component

I _RA (t) = cos (4 π / λR _RA (t))

and the quadrature component

Q _RA (t) = sin (4π / λR _RA (t)).

Now with this, adapted to the changed lighting geometry, Correlated reference function, so you get the full resolution again capability of the ROSAR system.

From Fig. 5 are for various values of β the results of the correlation S _OB (α _r ) between the received signal modulated by an angle of attack β and the reference function calculated for the plane rotary movement with constant angular velocity with λ = 0.23 m, R _gn = 265 m and H _o = 2.5 m with an opening angle of the antenna γ = 46 ° as a function of the angular displacement α _r . This shows that in this case no reference function S _RA (t) was used which was adapted to β. For distances to the target R _gn that are large compared to the rotor length L and the height H _o , the simplified reference function with the in-phase ( _RA (t)) and quadrature components ( _RA (t)) follows:

and

Further explanations regarding the clock, digitization, etc. are brought in DE-PS 39 22 086 and not the subject of the request for protection.

The circuit diagram of a processor for a ROSAR device according to FIG. 6 shows in its upper half a first channel with those modules that are proposed for generating the reference functions and in its lower half a second channel with those modules that receive the am Ground reflected signals are used. Thus, a geometry module I is provided in the first channel, which calculates various sizes and functions on the basis of the height H _{o of} the antenna above ground and other parameters, in particular the depression angle, the inclination angle and the length of the rotor arm, and a processor circuit 2 for dividing the illuminated area in individual distance intervals. This processor circuit 2 is connected to a processor module 3 , in which, based on the output signals of this circuit 2, the reference functions for the individual distance intervals are calculated and transferred to a memory 4 . In the second channel, the echo signals S _{e are} fed to a quadrature demodulator 5 and broken down into the in-phase and quadrature components I _e and Q _e . The two components are supplied to analog-digital converters 6 , at the output of which discrete samples are then available. These complex echo signals are then transferred to a memory 7 for correlation. In this memory 7 , the received signals S _E for the respective distance intervals are combined from the echo signals S _e associated with these intervals. The signals stored in the memories 4 and 7 are fed synchronously to a correlator 8 and correlated. The correlation result is shown on a display, e.g. B. a monitor 9 , shown and / or further fed to an evaluation device 10 .

With regard to the closer function, especially with regard to the Auftei the reference functions based on individual distance intervals and their Calculation is made to the above-mentioned DE-PS 39 22 086.

In addition to the described components, as illustrated in FIG. 6, a kinematic sensor 11 is connected. This sensor 11 delivers the value of an existing angle of attack β. If this angle β is not equal to zero, then the reference function - which is adapted to the geometry changed by β - is generated. To calculate the associated lighting parameters, refer to the publication: Dr.-Ing. H. Klausing - "Realizability of a radar with a synthetic aperture by rotating antennas" - MBB-UA-1150-89-Pub.

The processor circuit, as shown in Fig. 7, performs the calculation of the - due to the angle of attack β adapted to the changed lighting geometry - performed by reference function. Here, the kinematic sensor 11 detects the current angle of attack β and transfers it to the blocks 12 a and 12 b for calculating the projected rotor blade length L _PO at α = 0 ° and the height difference ΔH. The projected rotor blade length L _PO is entered into building blocks 13 and 14 , the height difference ΔH into building block 15 . In block 13 , the projected rotor blade length L _{p is} calculated as a function of the angle of rotation α and the rotor blade length L. The block 14 calculates with L _PO and the rotor blade length L the projected angle of rotation on the ground α _p as a function of the angle of rotation α.

With the help of L _p and α _p and other variables, such as distance to the respective distance interval R _gn , the height above ground H _o at β = 0 °, the height deviation ΔH at α = 0 ° and the rotor blade length L, the distance curve is in module 15 R _A calculated. The in-phase (I _RA ) and the quadrature component Q _{RA of} the reference function S _RA = I _RA + j · Q _{RA are} calculated in module 16 with the aid of the distance curve R _A. The operation of the entire processor is controlled by the clock 17 .

Claims (2)

1. Radar device with synthetic aperture based on rotating antennas (ROSAR) with at least one transmitter, one receiver and one antenna for transmitting and receiving radar pulses at the end of a rotating arm of a helicopter rotor or a turnstile above the rotor axis and a processor, in the first Channel the reference functions are generated for different distance intervals and in the second channel the signals reflected on the ground are received, all signals go into memory, from where they are fed synchronously to a correlator, the correlation result is displayed and evaluated and to correct those deviating from the ideal circular path Rotor blade movements during a revolution the processor is assigned a kinematic sensor, characterized in that the kinematic sensor ( 11 ) continuously measures the current angle of attack β of the rotor blades and, at a value greater than zero, the components ( 12 a, 12 b) for calculating the pr the injected rotor blade length L _PO at the angle of rotation α = 0 ° and the height difference ΔH and inputs these signals to the components ( 13, 14, 15 ), where in the component ( 13 ) the projected rotor blade length Lp is calculated as a function of the angle of rotation α and the rotor blade length L. the module ( 14 ) with L _PO and the rotor blade length L calculates the projected angle of rotation on the ground α _p and in the module ( 15 ) with the help of L _p and α _p and sizes such as the distances to the respective distance _interval R _gn , the height above Reason H _o at β = 0 °, the height deviation ΔH and the rotor blade length L the distance curve R _{A is} calculated. 2. Radar device according to claim 1, characterized in that the block ( 15 ) is assigned a further block ( 16 ) in which the in-phase (I _RA ) and the quadrature component (Q _RA ) of the reference function S are determined with the aid of the determined distance curve R _{A RS} = I _RA + j · Q _{RA is} calculated.