Device for measuring angles designated low-altitude targets

 

(57) Abstract:

Usage: in the low-altitude radar detection for measuring angles. The inventive contains three symmetrical horizontally directed spaced along the height of the receiving antennas 1, 2, 3, three receivers 4, 5, 6, a transmitter 7 elevation low-level circuit that allows for measurement of elevation angles low-level circuits in the selector low elevation angles above the ground. 1-4-7, 2-5-7, 3-6-7. 2 Il.

The invention relates to radar systems and can be used in low-altitude radar detection for measuring angles designated low-altitude air targets in the sector of small elevation angles above the ground.

The aim of the invention is the ability to measure angles designated low-altitude targets in the sector of small elevation angles above the ground.

In Fig. 1 presents a simplified block diagram of the device, conventionally a diagram of the above ground antennas and their radiation pattern.

The structure of the device includes the following elements: three symmetrical horizontally directed spaced along the height of the receiving antennas 1, 2, 3, the receivers 4, 5, 6 and the transmitter angle designated low-altitude targets.

Elevation work with the beam width in the vertical plane already.

The complex voltage amplitude of the echo signal at the output of one of the receiving channels is represented in the following form:

e-jkz[F()ejkhsin+F(-)e-jkhsin] (1) where the elevation angle of the target;

r the slant range from the location of the antennas on the earth's surface to the target;

- the complex gain of the receiving channel;

h height of the antenna above the ground;

2 / wave number;

wavelength;

F( ) is the normalized antenna pattern in the vertical plane in free space;

complex coefficient depending on the characteristics of the transmission system radar and target are the same for both antennas;

the complex coefficient of reflection of radio waves from an earth surface at a vertical or horizontal polarization.

Let us assume that the shape of the pattern F( ) is symmetric in the vertical plane, then F( ) F ().

It is known that at small slip angles of the complex coefficient of reflection of radio waves from earth -1 for any polarization of radio waves and any real characteristics of the earth's surface. With this in mind, the formula (1) can be simplified and written in the following form:

e-jkr[F()2ej/2th height above the ground. The lower and upper antenna and the receivers are the same. From the formula (2) shows that in the sector of small elevation angles, the phase shift of the echo signals at the output of the receiving channels of the upper and lower antennas is almost independent of the angle of designated goals and the voltage error at the output of the phase detector is close to zero. Therefore, the similar can't measure the angles designated low-altitude targets, and to accompany such targets in the sector of small elevation angles above the ground.

This goal is achieved thanks to the joint solution of a system of two transcendental equations with one unknown on the interval elevation of the working sector of the device

0, (3)

0, where Gm1, Gm2, Gm3the maximum gain of the lower, middle and upper antennas, respectively;

TO1TO2TO3the gains of the receivers associated with the respective antennas;

wavelength;

F1( ), F2( ), F3( )- normalized pattern of the respective antennas in the vertical plane in free space;

h1h2h3the height of the respective antennas above the ground;

U1U2U3the amplitude of the stress echo with whom her expression for the complex amplitudes of the voltages U1U2U3the echo signals at the outputs of the receivers of the lower, middle and upper antenna.

Un= j2 Ke-jkrFn()sin sin, (4) where n 1, 2, 3. Finding from the formula (4) the relationship of the amplitudes of the voltages U3/U2and U2/U1the echo signals at the outputs of receivers top, middle and bottom antennas, we get the system of transcendental equations (3) to determine the elevation angle of the target .

Elevation working sectors of each of the equations of this system has many roots. From this set, choose the root that is the same for the first and second equations of system (3).

However, there may be these private building antenna system, when among the many roots of the first and second equations of system (3) elevation operating sector will be more of the same. In such cases, the solution of system (3) is ambiguous and suggested the device will not function. Therefore, you should take special measures when building the antenna system, so that such ambiguity was not elevation desktop sector.

Ambiguity will not, if the height above ground of the top of the antenna h3is not a multiple of the height of rise h2h1the other two antennas is to the other antenna and covers only a relatively small (not more than 5-7) number of interference lobes of the lower antenna, occur due to the influence of radio waves reflected from the earth's surface.

In Fig. 2 shows the calculated dependence relations voltage signal and the argument of h1sin for a) proper construction of the antenna system (a) and (b) incorrect construction of the antenna system (b). For a given direction of the goal, which is marked by the arrow on these graphs crosses marked the roots of the first and second equations of system (3), and crosses in circles roots, the same for the first and second equations. In both cases the height of the antennas above the ground were chosen so that h22h1and h3Uh1. In addition, the bottom 1 and medium 2 antennas of the same, all the receivers are the same, i.e., TO1TO2= K3. In the case of (a) the pattern of the upper antenna 3 in the vertical plane was four times narrower than the antennas 1, 2 and covered about 5 interference lobes of the lower antenna, and in case (b) all three antennas were the same with the bottom antenna. As can be seen from the graphs (see Fig. 2), if built properly, the antenna system may unambiguous determination of the angle designated purpose, and at the wrong equation system 3 have many of the same roots and unambiguous the device is performed as follows.

As the antennas 1, 2, 3 can be used horizontally symmetric directional antennas (e.g., mirror or horn). The receivers 4, 5, 6 made by conventional superheterodyne circuit. Limitation of the signal amplitude in the path of the receivers is unacceptable. The identity of the amplitude and phase characteristics of these receivers are not required. Special calculator 7 is made in digital form and is a specialized computer for joint solution of a system of two transcendental equations (3) with one unknown and a broad selection of roots of these equations one is the same for both equations.

The dynamics of the operation of the proposed device is as follows.

Receiving antennas 1, 2, 3 receive echo signals low-level goals that come to the antenna as a direct radio wave and radio wave reflected from the ground. The receivers 4, 5, 6 amplify the echo signals, and convert, to an intermediate frequency and detects. The output voltage U1U2U3receivers on videocassete come to the transmitter 7, where they are converted into digital form. The computer 7 determines the angle designated low-altitude targets by the joint solution of equations (3) on the interval for the PURPOSES containing three symmetrical horizontal directed, spaced along the height of the receiving antenna, each of which is connected with the corresponding receivers, characterized in that the evaluator angle designated low-altitude targets, the first, second and third inputs connected to the outputs of the respective receivers, and the output is an output device, and calculating the angle q is produced by the following formulas:

< / BR>
< / BR>
where U1U2U3the amplitude of the voltage of the echo signals at the outputs of the receivers of the lower, middle and upper antennas, respectively,

the maximum gain of the lower, middle and upper antennas, respectively;

K1, K2, K3the gains of the receivers;

wavelength;

F1(), F2(), F3(a) normalized radiation pattern of the respective antennas in the vertical plane in free space;

h1h2h3the height of the respective antennas above the ground.

 

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