DE3135306A1 - Radar device - Google Patents

Description

Radar device

The invention relates to a radar device according to the preamble of claim 1. In particular, the Invention with a radar device which enables depolarization measurements of the backscatter.

In the case of radar devices ^K , it is necessary in some application cases to display a target with the simultaneous presence of clutter, for example an artificial or foreign vehicle on uneven terrain. The polarization characteristics of artificial objects are often different from those of the clutter.

The invention is intended to make it possible to determine the depolarization characteristics of selected received Determine radar backscatter signals so that the information obtained can be used as an aid to target characterization can be. Furthermore, a non-coherent radar device is to be created by the invention, which the Determination of the depolarization characteristics allowed.

To achieve this object, the invention provides for the radar device presupposed in the preamble of claim 1 the features specified in the characterizing part of claim 1.

In one embodiment of the invention, means are provided for a signal of predetermined linear polarization to send out. . .

For a better understanding of the invention this
explained in more detail below with reference to the drawings. Show it:

Fig. 1 is a block diagram of a first embodiment of the invention. !

Fig. 2 is a block diagram of a second embodiment!

Rungsform the invention, ι

Fig. 3 is a block diagram of a detail from ':
Fig. 1 or 2, '■

Fig. 4 A and B a modification of the first and
second embodiment,

Fig. 5 is an ellipse for the purpose of explanation!

of the Background of the Invention, · j

6 shows an adapted differential branch

as "magic T" and ■
7 and 8 detailed representation] 1 uncjon der I.

Processing circuits of FIGS. 1 and 2.

In the description the symbols V, H, VV,
VH, HV and HH used. V describes a first
linear polarization, which is shown below as
Example relates to a vertical polarization. H means
a linear polarization orthogonal to the first polarization, I where H is also only considered as an example in the following as horizontal polarization. If the mentioned sym- j

bole appear in combination, the first symbol indicates the polarization of a transmitted signal, while the | second symbol for the. Polarization of a selected reverse! Beam signal. So VH marks the horizontal

polarized component of a return signal as a result

ι the emission of a vertically polarized signal. i

In Figs. 1 and 2 are within circles
Reference _symbols A yv, A _VH , S ₁ , S ₂ » ^x 'Y> ^S 3 ^{and z} y ^ eicjl .. These symbols in the circles do not represent any circuit elements

rather, they denote equations in the Description are mentioned, and describe the signals at the points at which the associated connecting line to leads to the wiring of the circuit.

Referring first to FIG. 5, for example, when a vertically polarized signal A "is transmitted and backscattered from an artificial target, the return signals include vertically polarized components Ay" and horizontally polarized components Ayr ,. In general there will be a phase difference 0 between the components A _vv and Arrrj; _: and therefore the return signal is elliptically polarized (in the special case with 0 = n / 2 and when the amplitudes of the components are equal, the return signal is circularly polarized).

Thus, the resultant of the two components describes an ellipse in space, the main axis of which is inclined by an angle Γ with respect to a reference direction, and which has an amplitude ratio of its main axis to its minor axis which is equal to the tangent of e, where T represents the ellipticity and a value within of the range - ^ Af- L · £ ⁺ y "(f possesses. The angles T and Ys are dependent on the relative amounts of the two components and on the phase difference between the two components.

The implementation of a sent signal with a Polarization (e.g. V) through a target into a return signal of different polarization (e.g. elliptical) is known as depolarization.

The embodiments of the invention described in more detail below enable measurements of the various

nen parameters that are possible with the ellipse, so that one quantitative information about the depolarization characteristic receives. This information can be used to help characterize the target.

1 shows, by way of illustration, a non-coherent radar system with separate transmitting and receiving antennas. A transmitter 1, which contains a magnetron, transmits a pulse-shaped radar signal A _{v of} a frequency in the microwave range, e.g. B. 10 GHz (Giga-Hertz), the signal having a vertical linear polarization. A receiving antenna 2 receives backscatter signals of the components A _yy and A _VH with vertical or horizontal polarization and leads them to an orthomode transmitter 3 working in the correct sense. The transmitter 3 separates the vertically and horizontally polarized components and supplies them separate outputs.

The signals at the outputs are high-frequency signals that can be described as follows: ■

^A VV ^{= a} l ^exp (^ 3 / ^exp ftot). )

) Equation (1)

^A VH ^{= a} 2 ^exp [Hf ⁺ ^ M

a, and a2 represent amplitudes jJJ 'is a phase, which arises randomly from pulse to pulse due to the incoherence of the magnetron; © is the phase difference between the two signals; CJ is the radar frequency, and t represents time.

The time dependence in the form of the exponent (j £ Jt)

is neglected in the further description. ^v

The two signals are fed to a 3 dB coupler 4, which _{generates the following signals S 1} and S ₂ at the respective outputs:

5 ₁ = ^ a ₁ + a ₂ exp [j (0 + f / 2) Jj exp (j

⁵ 2 ⁼ i ^a l ^{+ a} 2 ^exp \ j & ~ T ^{/ 2)} ] J ^ex P [

Since the amplitudes a, a ₉ and the phase 0 'are important

i J- Z _s

Parameters are, it matters; that they are precisely preserved and protected before the signals A _vv and A _v "are combined together to form _{S 1 and S 2.}

The signals are fed to mixer stages 5 and 6, respectively, where they are mixed with an oscillator signal LO which is generated by a local oscillator 7 in order to convert the signals into intermediate frequency signals of the same effective values S ₁ and S ₂ . From the intermediate frequency circuits 8, 9, the intermediate frequency signals S, and S ₂ pass to square detectors 10 and 11, which generate signals of the following values χ and y:

x = S ₁ -S ₁ * = IsJ ² = ^a ! ² + ^a> 2 ^{2 + 2a} i ^a 2 ^Cos ^ + ^ 2) Equation ^

V = S _n Sn * = IsJ ² = 2 + a ₉ ² + - 2a _ia9 cos (j3 - ^ 2) Equation W.

ζ "2 I 21 - ° -j_ Zi ^

where S- * is the complex conjugate value of S.

The processing circuit 14 is responsive to you applied signals to generate a signal which represents the following parameter k_:

k = yx . = 2a-, a ₂ sin 0 equation (4),

^a l ^{+ a} 2

• · β. 8 · »4 0

- 11 -

and from k_ the arrangement derives the ellipticity 7 * mentioned above in connection with FIG. 5, where the equation * £ "= 1/2 aresin (Ji) applies, as is shown below. As can be seen from this equation, makes the invention of a trigonometric relationship - in this case sine - between the parameter k_ and the ellipticity 2 "use.

An example of the processing circuit 14 of FIG. 1 is shown in FIG. This circuit is an analog processor. It comprises inputs 70 and 71 for receiving the signals χ and y_, an addition amplifier 72 which generates the output value - (x + y) and a subtraction amplifier 73 which generates an output value - Cy-x), and a ratio circuit 74 which a Provides a signal with the value k. The analog processor also includes an analog function generator which generates a signal of the value L from the signal with the value k.

The signals χ and y are via LW circuits (Long wave circuits) led to a digital processing circuit 14, which in the form of a microcomputer may exist. Each of the LW circuits is constructed as shown in Fig. 3 and comprises amplifier circuits 30, 31, one Sample and hold circuit 32 and an analog-digital converter 33, which the digitized signals je and y_ to the Processing circuit 14 leads.

The derivation of

T «1/2 aresin (k)

given. An arbitrarily elliptically polarized limpfang impulse signal can be represented as follows:

cosf - sin ^ "] (" cos t E = AI Π

■ + cost f / jsin? "

"J L

- 12 -

where A represents the signal amplitude. Ϋ means the orientation of the main axis of the ellipse with respect to a reference direction (-90 ° £ Ψ £ 90 °),
and 2 "is the ellipticity (-45 ° £ T £ 45 °).

The function tan t is formed by the amplitude ratio of the minor axis to the major axis of the ellipse.

The two components of the vector E_ represent the represent vertically and horizontally polarized components of the received pulse signal.

[cos T cos c ~ - j sin Ϋ sin L Isin f ~ cos TT + j cos V "

d. H. : -E =

₁ = arc tan (tanV'tant)

= arctan

0 = P ₂ ι + 0 ₂ - arctan (tan 2t). (sin 2f) follows S \ tl0 -----
I. sin IL and further : i - cos ² 2r _CO s ⁱ / 2

• a · ··· «no« «» e ύ

- 13 -

2
& ± & 2 = τ I sin 2ψ + j cos

2
sin 0 = A sin

a ₂ ² = A ²

results from equation (4):

2a-, a2 sin 0

k = --sin 2t equation (5)

a τ L ·. "f · a η £

Thus for the ellipticity we get; TT = \ aresin (k).

It should be pointed out that the ambiguity of the value of aresin has been resolved because ^ within the range _ 45 ° ^ T ^. + 45 ° is assumed and that it is not necessary to know a and a ^ separately in order to determine L.

For the left elliptical polarization t "^ o applies, and for the right elliptical polarization V > o.

The orientation of the axes of the ellipse (and thus also the phase difference of the two components) is given by the following equation:

.i. 1 . , tan 2T ", _,. _{,, r} *

γ = "2 arcsm ( ) Equation (6; "

- 14. ■ - ■■■

Because in the above-described system a ,, a ₇ and thus sine are not all known separately, ^ is indeterminate.

FIG. 2 shows an extension that can be made in the system ^: according to FIG. 1 in order to resolve <t and therefore to determine ψ. There is a third signal S-, according to the following equation

3 ⁼ f ^a l ^{+ a} 2 ^exp ^ / 3) [

S ₃

derived,

where a ,, · a2, 0 and Y have the same meaning as in the above-mentioned equation (1).

In FIGS. 2 and 6, the signal S _{3 is} derived from the outputs of the transformer 3 in the following manner: 3-dB couplers 20 and 21 connect the outputs of the transformer 3 to collinear arms 61 and 62 of a hybrid, respectively (Differential branch in the form of a "magic T.") 60. The E-arm 63 of the differential branch 60 is coupled to a termination 22, while the H-arm 64 supplies _{the output signal S 3.} ·

The signal S ₃ at the output or on. the H arm 64 of the differential junction is a high frequency signal. It is fed to a mixer 23, where it is mixed with the local oscillator signal LO of the oscillator 7 and converted into an intermediate frequency signal. From the intermediate frequency circuit 24, the intermediate frequency signal S- arrives at a square detector 25 in order to generate the following signal ζ:

(ι 2 '2 2
S ₃ ~ ^a i ^{+ a} 2 ^{+ 2a} l ^a 2 ^coS ■ # '. Equation (7).

'- 15 -

The signal ζ is fed to the analog processor. 14, which executes the following equation and a Generates signal that represents tan ^:

tan 0 = equation (8).

Furthermore, derived from equation (5): tan 2Γ = k / (lk ² ) ^1/2 .

If one replaces tan ^ and tan lT in equation (6), one gets Ψ without ambiguity because of -90 ° ^ ¥ * " ^ 90 °.

An example of the processing circuit 14 of FIG. 2 is shown in FIGS. This processing circuit is an analog processor. It has inputs 80, 81 and 82 to receive signals y, χ and ζ, respectively. The input 82 leads to an amplifier .83, which generates a signal -2z from ζ. The inputs 80 and 81 lead to a subtractive amplifier 85 for forming a signal value - (x-y) and to an additive amplifier 84, which also has the Output signal of amplifier 83 receives a signal with the value - (- 2z + χ + y). The processor also includes a ratio circuit 86 which controls the output signals amplifier 84 and 85 receives and forms a signal of value tan ^ J.

The processor of Fig. 2 also includes a processor shown in Fig. 7 for processing the signal having the value f to be generated, and in addition, a further analog function generator 76 is to generate a signal with the value tan 2 ^ provided.

The processor shown in Fig. 8 also has a ratio circuit 87 which the signals tan 2t and

- 16 -

tan φ receives and an analog function generator 88
is connected downstream, which generates signals with the value ψ.

Alternatively, the signal ζ to a digital processor 14 in the form of a microcomputer via another
Long wave circuit (LW) are guided, which is shown in FIG.

Referring to Fig. 4, a modification will now be made of the system according to FIGS. 1 and 2 described.

Fig. 4 shows part of a non-coherent one

Radar system with a common transmitting and receiving antenna. This system enables vertically and horizontally polarized signals to be transmitted and received and sent sequentially to process. The part shown in Fig. 4A replaces the transmitter 1, the receiving antenna 2 from Fig. 1 or 2 and the transmitter 3 from Fig. 1 or 2.

A transmitter 40 (e.g. a magnetron) guides you
switchable polarizer 42 to high frequency energy. The polarizer 42 is controlled by a pulse source 41 which generates switching pulses to control the polarizer 42 in such a way that the transmitted pulses are either vertical
V or horizontally H are polarized. The signals are then passed to an antenna 45 via a duplexer 44 (transmit / receive switch), which transmits the return signals to the
Transmitter 43 (orthomode transmitter) conducts. ■

The output signals of the transmitter 43 are fed to the two channels via the coupler 4 from FIG
to generate the signals χ and y, or via the coupler 20,
21 and 4 in Fig. 2 to the three channels, to the signals x, y
and to generate ζ. However, the signals x, y and ζ that

arise due to the transmitted pulses with vertical polarization, are separated from those signals that ■ adjust themselves on the basis of the transmitted pulses with horizontal polarization before they are sent to the processing circuit 14 be guided. -

Accordingly; is between the processing circuit 14 and each square detector 10, 11 and 25 a de-multiplexer inserted. An example of a de-multiplexer is shown in Fig. 4B with respect to that channel to which only the signal x_ is assigned.

The de-multiplexer comprises a pair of electronic switches 47 and 48, which are jointly connected to the output of the detector 11 are switched. The electronic switches 4 7 and 48 are activated by the switching pulses of a pulse source 41 (Pig. 4A) controlled, the switch 47 directly and the switch 48 via an inverter 46 to the pulse source 41 are connected. The switches 4 7 and 48 alternatively close synchronously with the transmission and reception of the high-frequency pulses vertical and horizontal polarization in order to transfer the corresponding return signals x "and x" to the

V π

to lead processing circuit 14 (if necessary via long wave circuits 49 (LW), as shown in Fig. 3) -. The processing circuit comprises a sufficient number of, for example, analog processors as shown in FIGS. 7 and 8 to process signals of the values tL and Y <. from the signals. Xy ₁ Vtt and z., As well as signals Ln and Tj, from the signals ^X H ^{'VH un <^ Z} H ^{to erzeu} <? ^en · ■

Benutzt'wird when the system shown in FIG. 2, the system is shown in FIG. 4 common to information on the backscattered scattering matrix to obtain a target, dos.son scattering does not vary within a period between the pulses. As I said, be vertical and horizontal

linearly polarized signals sent sequentially. It is It is not important that the two sets of the transmitted pulses are polarized vertically or horizontally, only it is it is necessary that they are orthogonally polarized. For the sake of simplicity, however, a system is described above and analyzed below which vertically and horizontally polarized signals sequentially emit.

The value of 0 is denoted by 0 ^ _v if the transmitted wave is vertically polarized, and the corresponding value for the horizontal polarization is 0 "..

f. ^HV

. The corresponding values a. let with a Y and a, respectively. designated.. ,

The target scatter matrix for a radar system with a common transmitting and receiving antenna is then:

exp (-; I 1

S = exp

a ^H a ^H
a l ^a 2

^ex p 0

where } f is an indeterminate phase (if a non-coherent radar system is used). The values of 0 ^ ,. and 0 ^

are determined as described above by using equation (8). The values of a, and a- as well as of a, ^H and a "are derived by solving two (two combinations) of the three equations (2), (3) and (7) for a. ^ And a2 for-each of the two Polarizations. The. Solving these equations can be accomplished in a known manner using either an analog or digital technique.

β A β · β 0 ti · * 0 * 0 α β < «6

ft Λ β # β - rt β <5 Λ ρ

- 19 -

The requirement that a "= a" enables data for successive pulses to be cross-correlated are.

In order to measure the depolarization accurately, it is necessary that the relative amplitudes and the relative phases of the received two orthogonally linearly polarized components A _vv and Ay _{H are} not disturbed. In the examples of the invention described above, the two components Ay _V and Ay _{H are} separated (but not processed in any other way) and then combined in a predetermined manner before they are subjected to processing such as conversion to an intermediate frequency, amplification and detection or demodulation are. This ensures that the information relevant to the elliptical measurements t * and Y is retained during processing. Thus, quantitative information about the properties of the depolarization can be obtained and used as an aid to target characterization when using a non-coherent radar system of the type described.

Claims (19)

EIKENBERG & BRUMMERSTEDT PATENT LAWYERS IN HANOVER EMI LIMITED .100 / 585 Claims Radar device for generating measurement signals in order to derive quantitative measurements about the ellipticity as a consequence of the depolarization of a transmitted polarized signal, characterized by the following features: An input for receiving an elliptically polarized high-frequency signal, Coupling means connected to the input in order to connect the two orthogonally linearly polarized high frequency components which said elliptically polarized Shape the signal, with the relative amplitude. the and phases of the two components essentially protected and preserved, combination means for the formation of the first and second different intermediate frequency combinations of the components, Processing means for evaluating said combinations in order to generate said measurement signals, and
Means to one from the measurement signals mentioned Derive parameters, which by a trigonometric function related to the mentioned
Ellipticity. 2.. · Radar device according to claim 1, characterized in that the trigonometric puncture is a sine function. 3. ' Apparatus according to claim 1 or 2, characterized in that further means are provided for the value of the
Derive ellipticity from the parameter mentioned. 4. Radar device according to one of the preceding claims., Characterized in that the radar system is a non-coherent system. · 5. Radar device according to one of the preceding claims, characterized in that a third related high-frequency combination of the components is formed by the combination means, and that the processing means further means
in order to derive the orientation of the elliptical polarization of the received signal from the measurement signals mentioned. . ■■ ".- ■" 6. Radar device according to one of the preceding claims, characterized in that means for sending a signal
predetermined linear polarization are provided. 7. Radar device according to claim 6, characterized in that means are further provided to alternatively a
Signal with a first linear polarization or a
Signal with a linear polarization orthogonal to the
emit first linear polarization. . 4 Q · 4) · O * 4 Ο · «· 8. Radar device according to claim 7, characterized in that the processing means further contain means for deriving the relative amplitudes and phase differences of the components of the relative target scatter matrix from the measurement signals mentioned. 9. Apparatus according to one of the preceding claims, characterized in that either a common antenna is used for both transmission and reception, or that the two antennas are arranged so close to one another that considerable phase differences are avoided. 10. Radar device according to one of the preceding claims, characterized in that the processing means comprise means for converting said high-frequency combinations into an intermediate frequency. 11. Radar device according to one of the preceding claims, characterized in that the processing means have amplifiers for amplifying the combinations. 12. Radar device according to one of the preceding claims, characterized in that the components have values which relate to the following equations: A ₁ = a- ^ exp (J3 ") A ₂ = a ₂ exp Pj (JT + β ) J and that the combination means include the combinations in the following Transform values: exp (j ^) 5 ₁ = Yes ₁ + a ₂ exp fj (0 + * & /: 5 ₂ = Ta ₁ + a ₂ exp £ j (0 - ^ / 2)] ¹ ^ where the following meanings are used: A-, identifies the component received, which has the same linear polarization as the transmitted signal, A „identifies the component received, whose Polarization is orthogonal to that of the transmitted signal, a-, and & 2 represent amplitudes, y means any phase, and β stands for the phase difference between the components mentioned. 13. Radar device according to claim 12, characterized in that the processing means further comprise means to convert from said measurement signals. Signals of the values x, and y, 11 Z
S2I ■ of the mentioned combinations S, and S ₂ are. 14. Radar device according to claim 12 or 13, characterized in that the combination means form a further combination S3 with the following value: ^S 3 ⁼ J ^a l ^{+ a} 2 ^ex P (J 0) f exp (jy). 15. Radar device according to claim 14, characterized in that the processing means further comprise means to derive a further measurement signal which the S, J of the mentioned combination is S ₃ . 16. Radar device according to one of the preceding claims, characterized in that the processing means comprise a square detector. ■ 17. Radar device according to claim 13 or 15, characterized in that further means are "provided in order to derive the parameter k from the measurement signals, wherein k = (yx) / (y + x) = sin 2 T and Y is the value of the ellipticity. 18. Radar device according to claim 17, characterized in that further means are provided in order to derive the value of the ellipticity "from the parameter k, where ■ <v 1
L ~ ~ 2 aresin k is. 19. Radar device according to claim 18, characterized in that the means for deriving also derive a measurement γ of the orientation of the ellipse, wherein ψ = "2 aresin J tan 2 T. (2z - χ - y) / (yx) j