JPS6056273A - Radar equipment - Google Patents

Abstract

PURPOSE:To accurately measure the slant range on an antenna boresight axis, by changing the phase of a phase shifter corresponding to an antenna elevation angle while changing a range gate amplitude. CONSTITUTION:The monopulse synthesizer of an antenna 3 is formed of first hybrids 15-1, 15-2, second hybrids 16-1, 16-2 and a termination device 17. A phase shifter 18 is provided between the first hybrid 15-1 and the second hybrid 16-2 and driven by a drive circuit 19. After all, the phase of the phase shifter is changed corresponding to an antenna elevation angle and an elevation difference channel signal reflected from the earth is made symmetric in the amplitude thereof before and after the center of the slant range on an antenna boresight axis while range gate amplitude is changed to make it possible to enhance the measuring accuracy of the slant range.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a radar device, and relates to a method for measuring the distance from an antenna on the antenna boresight axis to the ground [Prior Art J] - In order to measure the distance from the antenna on the antenna boresight axis, the device uses a monopulse antenna and uses its 411 channel signal toerpation difference channel signal. , whose configuration is shown in FIG. In the figure, (1) is the transmitter, (2) is the transmitter/receiver switch, (3) is the antenna, (
4) is a receiver, (5) is a distance tracking circuit, 2 is a monopulse sum channel signal, and Δ is a monopulse difference channel signal.

A conventional radar device is configured as described above, and a pulsed transmission signal generated by a transmitter (1) is sent to an antenna (3) via a transmitter/receiver switch (2). The transmitted signal is input to the sum channel of the antenna (3) and is irradiated toward the ground on the antenna boresight axis. The transmitted signal reflected by the ground is received by the antenna (3) and output as a monopulse sum channel signal Σ, a monopulse elevation difference channel signal Δ, and then sent to the receiver (4).
), the elevation difference channel signal is phase-detected by the sum channel signal Σ and sent to the distance tracking circuit (
At the same time, the sum channel signal Σ is envelope-detected and sent as a video to the distance tracking circuit (5). The distance tracking circuit (5) uses a range gate for the two videos to extract only the necessary signals, and for the sum channel video, the receiver (5) extracts only the necessary signals so that the output is constant.
4) is used for gain control, and the difference channel video is used to control the position of the range gate so that its output is zero. Measure the distance from the temporal position of the range gate to the ground on the antenna boresight axis. - The antenna BL angle controller (6) commands the antenna elevation angle θD to the antenna (3) to change the angle of the antenna boresight axis from the horizontal direction.

By the way, as shown in Figure 2, the radar device (7) is at an altitude of H.
When P is moving horizontally parallel to the ground (8), the antenna boresight axis in the antenna elevation angle θD direction (
9) To measure the above direct distance, the distance from the antenna to the ground differs in the vertical direction centered on the antenna boresight axis, and the angle of incidence of radio waves to the ground also differs, so the antenna boresight @ (9) Even if the gain characteristics of the sum beam GO and the difference beam αυ with respect to ) are symmetrical, the receiving power levels will not be equal. Here, the angle of incidence of the radio wave with respect to the earth is θ (received power PΣ of sum channel signal regarding L'C and received power 1
By subtracting °Δ, it can be expressed by the following formula.

1 C: Transmission peak power λ: Free space wavelength LFT: 4D transmission path loss from transmitter to antenna 17RT: Transmission path loss from antenna to receiver LR = Radome transmission loss C: Speed of light τ: Transmission pulse Yamabatake θA: Andena azimuth direction 3 (DJ beam width σ0(: Clutter anti-reflection per unit area!, J coefficient a) Slant range in 20 directions α: Atmospheric depth ratio GΣ(θ-θ7.): Sum channel Gain function G, (θ
-θD): Difference channel gain function The gain function of the antenna can be expressed by the following equation in the vicinity of the main beam of the sum channel.

Small (θ-〇,)-Gotz-(θ-0n)/L: (
4) Mei (θ−θo) = 0.40. sm-(θ-θ
oVo8θE(5) Also, σ″(θ)d changes exponentially with respect to the incident angle θ, so it is expressed by the following formula, ・(o') −iu'−β 0):Gl However, β,
0 is a constant, hood is the maximum gain of sum chara, le, θE ('
The beam width is 3 rl I3 in the weaving/bation direction. t41. f51. : 61 formula “, I), +2)
Substituting it into the equation and standardizing it by the received power in the surface distortion when the monomantic angle θD is the same.

(I prediction θ) (7) −σθ1゜0 σUD 0 where Kl = Koi; tQ−β+00 and temporary −Dtoo
"" +91 The sum channel signal shown by equation (7) is envelope-detected by the receiver (4), and the elevation difference channel signal shown by equation (8) is subjected to phase detection with the sum channel signal by the receiver (4). be done. The sum channel video V and the elevation difference channel bipolar video V after being detected by the receiver (4) can be expressed by a quadratic equation.

However, if −1〈(θ−θo)/θE＜1, that is, α[,6
Equation 9 holds true. In addition, the atmospheric attenuation rate α was ignored because it was a small value. Figure 3 shows the video signal obtained by numerical calculation from the 01゜0υ formula, and Figure 3(a) shows θE-10°.
It was at that time.

FIG. 3(b) shows the case when θ=30°. In the figure, tl
a is a sum channel video, Ql is an elevation difference channel bipolar video, and 04) is a range gate. The time to when the polarity of the elevation difference channel bipolar video α is reversed and becomes zero is 'o=2R
o/C0τ/2 However, the amplitude of the video at times before and after this time to is different, and the distance is long.

That is, the video of the signal reflected from the difference beam +I11 above the antenna boresight axis (9) will have a smaller amplitude than the video from the difference beam αυ below.

Therefore, even if the range gate α4 is set around time to, its output will not become zero. When the antenna elevation angle θD becomes small, the difference channel bipolar video 03 spreads on the time axis, and if the range gate width is fixed, the range gate LJ4
1 output level has decreased. Under such conditions, the distance tracking circuit (5) controls the range gate position so that the range gate output of the elevation difference channel bipolar video (1) is always zero, and adjusts to.
o = zI'LJ (! + τ/2 from slant range Ro
-@3'! put out However, the upper and lower 4e elevation difference channel bipolar video a3 has an asymmetrical amplitude before and after the time to, and spreads out on the time axis, so the center of the range game 1 (+4) is at the elevator. There was a drawback that the difference between the channels and the video 03G shifted from the zero point, resulting in calculation of distant distances.

[Summary of the invention]

This invention was made with the purpose of improving such drawbacks, and by installing a phase shifter and a drive circuit in the monopulse synthesizer of the antenna, the above-mentioned adjustment is performed according to the angle formed between the antenna boresight axis and the ground plane. By changing the phase of the phase shifter.

By changing the gain of the difference beam above and below the antenna boresight axis, we can make the amplitude of the difference channel signal reflected from the ground symmetrical around the slant range on the antenna boresight axis, and The present invention proposes a radar device that can greatly improve the measurement accuracy of slant range by changing the gate width and improving the error sensitivity of the range gate output signal.

[Embodiments of the invention]

FIG. 4 is a schematic configuration diagram of a radar device showing an embodiment of the present invention. (1) to (6) are almost the same as the conventional device described above. The transmission signal from the transmitter (1) is passed through the transmitter/receiver switcher (2+) to the sum channel terminal (2+) of the antenna (3).
IT). The monopulse synthesizer of the conventional antenna (3) is connected to the first hybrid (15-IX15-2
), the second vibriat (1610162) and the terminator fi7)f, but in this invention, in order to control the gain difference between the two peaks of the difference pattern, the first) -1) and the second 7-Ibrid (16-2), a phase shifter is installed between the drive circuit QI
The phase shifter θQ is activated. This phase shifter 08 functions to give a phase difference ψ above and below the monopulse antenna opening 0dIi, but this shifted difference ψ is 2 of the difference beam 0υ.
This will change the level difference between the two peaks and the zero point angle. The amount of change Δθ of the zero point with respect to the phase difference ψ and the difference beam 2
The difference ΔA in V can be approximately expressed by the following equation based on the simulation results of the antenna pattern.

”A = 15.6 jan (ψ/a) (dB)
If in the a:i02 equation, ψ delays the phase of the lower half of the antenna aperture, the zero point will move downward by Δθ.

Nao, in the case of conventional radar equipment, the difference in amplitude of the embellishment difference channel bipolar video (14) can be calculated according to the antenna elevator angle θDK by the α0 formula, so the shift required to compensate for this difference in amplitude is If the phase edge of the phase converter OE is set and the zero point movement is corrected using formula 02 using the antenna + L angle controller (6), the electric piano 7-I difference channel biholer video a can be adjusted to the zero point. In addition, when the antenna elevation angle θD becomes small, the error sensitivity of the range gate output can be prevented from decreasing due to the elevation difference channel bipolar video o3 spreading greatly on the time axis. In order to do this, the width τ6 of the range gate may be set using formula 04.

r(, = kB11CotθD (141 and k is a constant.

When the antenna +4L angle controller (6) sends the information of θD to the distance tracking circuit (5), the distance tracking circuit (5) determines the width of the range gate based on the equation 04]. In this way, the accurate slant range of 61 positions becomes 5 positions.

Figure 5 shows the time axis waveforms and range gates of the sum channel video αl elevation difference channel bipolar video (11) according to the present invention. ) is θF, = 30'
In both cases, the elevation difference channel high hole height has an amplitude characteristic that is symmetrical with respect to the zero point, and the range gate width also changes in accordance with the spread of the video.

[Effects of the Invention] As explained above, the present invention installs a phase shifter and a drive circuit in the monopulse synthesizer of the antenna, and adjusts the angle according to the antenna elevation angle.

Along with changing the phase of this phase shifter.

A simple 1n1 configuration that only changes the range gate width has the effect that the slant range on the antenna borezite axis can be accurately measured even at a shallow elevation angle.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional radar device, FIG. 2 is an operational diagram of a conventional radar device, FIG. 3 is a diagram showing a received video signal of a conventional radar device, and FIG. 4 is an embodiment of the present invention. Fig. 5 is a diagram showing the effect of improving the received video signal of the radar apparatus according to the present invention. switch,
(, 31 is the antenna, (4) is the receiver, (5) is the distance tracking circuit. (6) is the antenna FJ angle controller, (7) is the ladder device, (8) is the ground, (9) is the antenna poazite axis, (
[14 sum beam, OI) is the difference beam, o2 is the sum channel video, 631dx v hesi, n difference channel biholer video, Q41H1, -ngegate, α9 is the first hybrid, QQ(ri?i:2's Hybrid, αη is the terminator, QID is the phase shifter, (11 is the drive circuit, (A) is the rotation drive unit, θ is the incident angle to the ground, θD
is the antenna elevation angle, 11 is the altitude, rLn is the slant range on the antenna boresight axis, τ is the transmission pulse width, and 0 is the speed of light. Note that the same reference numerals in the figures indicate the same parts.

Claims (1)

[Claims] Using the sum channel signal and the elm-pelsion difference channel signal of a monopulse antenna. In a radar device that measures the distance from the antenna on the antenna boresight axis to the ground, a phase shifter drive circuit is installed in the monopulse synthesizer of the antenna, and the angle between the antenna boresight axis and the ground plane is The phase of the phase shifter is changed accordingly to make the elevation difference channel signal reflected from the ground symmetrical about the intersection distance between the antenna boresight axis and the ground, and the range gate width is changed. A radar device characterized by at least accurately measuring the distance from an antenna on the antenna boresight axis to the ground.