JPH0410031B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a radar device, and particularly to a radar device that improves angular resolution by utilizing the Doppler effect produced by moving an antenna. .

[Conventional technology]

The synthetic aperture method, which utilizes the Doppler effect due to antenna movement, is widely known as a method for achieving higher angular resolution than that determined by the aperture of a real antenna. The principle of azimuth compression using the synthetic aperture method is described in the literature FT Urabii, R.
K. Mohr, AK Huang, “Microwave
"Remote Sensing (Active and Passive)", Volume 2, pp. 630-745, Addison-Wesley Publishing Company (1982).
(FTUlaby, RKMoore and AKFung,
Microwave Remote sensing (Active and
Passive)”, vol., pp630-745, Addison−
Wesley Publishing Company (1982)). Most radar devices using the synthetic aperture method are installed on flying objects such as aircraft and artificial satellites, but this principle can also be applied to ground use by moving the antenna, as described in the above document. If a device is constructed based on this, a radar device shown in FIG. 2 can be constructed. In the figure, 1 is a mobile antenna, 3 is a transmitter/receiver switch, and 4 is a mobile antenna.
is a high frequency amplifier (hereinafter referred to as RF amplifier), 5 is a mixer, 6 is an intermediate frequency amplifier (hereinafter referred to as IF amplifier), 8 is a phase detector (hereinafter referred to as PSD), 9
is a π/2 phase shifter, 10 is a video amplifier, 11 is a local oscillator (hereinafter referred to as STALO), 12 is a coherent oscillator (hereinafter referred to as COHO), 13 is a transmitter, 14 is an antenna driver, 15 is an analog/ Digital converter (hereinafter referred to as A/D), 16
is an input buffer memory, 17 is a fast Fourier transform means (hereinafter referred to as FFT), 1
8 is a square law detection means, 19 is an output buffer memory,
20 is a display, 21 is a receiver, and 22 is a signal processing device.

Further, FIG. 3 is a diagram for explaining the operating principle of this type of radar device, and 30 in the figure is a target.

The operation of this type of radar device will be described in detail with reference to the figures. A transmission pulse signal generated by the transmitter 13 is radiated from the antenna 1 toward the target 30 via the transmitter/receiver switch 3. A signal reflected by the target, that is, a radar echo, is received by the antenna 1 and input to the receiver 21 via the transmitter/receiver switch 3 . The received signal input into the receiver 21 is first
After being amplified by RF amplifier 4, it is amplified by mixer 5.
It is mixed with the STALO11 output and converted to an intermediate frequency. Furthermore, it is amplified with IF amplifier 6, and with PSD8
After being phase detected using COHO 12 outputs and π/2 phase shifter 9 outputs and converted to a video signal,
The video amplifier 10 amplifies the signal to a level suitable for the signal processing device 22, and outputs it as two so-called I and Q video signals. These two video signals, I and Q, are input to the signal processing device 22, first converted into digital video signals by the A/D 15, and stored in the input buffer memory 16. While moving the antenna at a speed V using the antenna driving device 14, the above operation is repeated until the necessary data is collected, and then azimuth compression is performed using the FFT 17.

Here, the principle of azimuth compression will be briefly described.

As shown in FIG. 3, where L is the movable distance of the antenna by the antenna driving device 14 and V is the antenna moving speed, the observation time T is given by T=L/V (1). At this time, if the angle between the traveling direction of the antenna and the target direction seen from the antenna is θ, then the Doppler frequency d caused by the movement of the antenna is expressed as d=2V cosθ/λ using the transmission wavelength λ...(2) becomes. Therefore, the Doppler frequency difference Δd caused by the angular difference Δθ is Δd=2V sinθ/λ・Δθ...(3) Therefore, if the frequency resolution of FFT is Δ=1/T, then the angular resolution is Δθ is Δθ=λ/2VT sinθ =λ/2L sinθ (4), which corresponds to expanding the antenna aperture length to 2L sinθ.

In Equation 2, since the transmission wavelength λ and antenna moving speed V are known, the Doppler frequency d
By measuring the angle θ, the angle θ can be determined using the resolution Δθ.

As described above, the result of azimuth compression using FFT is converted into power using the square law detection means 18 for each Doppler frequency, that is, each angle θ, and is stored in the output buffer memory 19. Thereafter, the display unit 20 converts and displays the brightness level according to each power.

In the conventional radar of this type, the azimuth compression is performed on the assumption that the Doppler frequency of the received signal and the angle have a one-to-one correspondence, that is, that the target is stationary.

[Problem that the invention seeks to solve]

Conventional radar devices utilize the one-to-one correspondence between the Doppler frequency d and the angle θ in order to improve the angular resolution as described above. Therefore, when the target is moving, the Doppler effect due to the movement of the target is superimposed on the Doppler effect due to the movement of the antenna, resulting in an error in calculating the angle of the target. For this reason, there was a problem in that it was not possible to observe moving targets.

This invention was made to solve these problems, and even when the target is moving,
The objective is to obtain a radar device that can observe a target with an angular resolution higher than that determined by the aperture of an actual antenna.

[Means for solving problems]

The radar device according to the present invention includes a fixed antenna and a receiver connected to the antenna, and replaces the IF output of the signal received by the fixed antenna with the COHO signal of the receiver connected to the mobile antenna.
It is configured to be used as a local signal for PSD.

[Effect]

In this invention, since the IF output of the signal received by the newly added fixed antenna is used as the PSD local signal of the mobile antenna receiver, even if the target is moving, Doppler effect due to PSD
You can cancel everything. Therefore, in the signal processing device, the angular resolution can be improved by performing the same processing as when the target is always stationary, regardless of whether the target is moving or stationary.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a radar device according to an embodiment of the present invention. In the figure, 2 is a fixed antenna, 7 is an automatic gain adjuster (hereinafter referred to as AGC), and 23 is a receiver for the fixed antenna. 1 to 22 indicate the same device or means as the conventional device.

Mixer 5 mixes the output of COHO 12 with oscillation frequency _IF and the output of STALO 11 with oscillation frequency _LO to create a radio signal with frequency _LO + _IF , and sends it to transmitter 1.
3, the signal is amplified and pulse modulated, and is emitted toward the target from the fixed antenna 2 via the transmitter/receiver switcher 3.

Now, assuming that the Doppler frequency due to the movement of the target is _T , the signal of frequency _LO + _IF + _T reflected by the target is received by the fixed antenna 2 and the mobile antenna 1 at the same time. The signal received by the fixed antenna 2 is input to the receiver 23, amplified by the RF amplifier 4, and then sent to the mixer 5 to be output to STALO 1 at the frequency _LO .
1 output and converted to frequency _IF + _T ,
It is further amplified by IF amplifier 6. In the receiver 23 on the fixed antenna 2 side, the output of the IF amplifier 6 is
The AGC 7 adjusts its output level to be constant, and the AGC 7 output is supplied to the receiver 21 on the mobile antenna 1 side as a local signal of the PSD 8. On the other hand, in the RF amplifier 4 in the receiver 21 on the mobile antenna side, since the antenna 1 is moving, the resulting Doppler shift _d is superimposed, and the received signal frequency becomes _LO + _IF + _T + _d . . This received signal is amplified by the RF amplifier 4, mixed with the STALO 11 output at the frequency _LO by the mixer 5, and converted to the frequency _IF + _T + _d .
It is amplified again by IF amplifier 6. The output of the IF amplifier 6 is sent to the AGC of the receiver 23 by two PSDs 8.
Phase detection is performed using the output of 7 as a local signal,
It is converted into two video signals, I and Q, and amplified by a video amplifier 10. At this time, the frequency of the local signal of PSD8 is _IF + _T , and IF amplifier 6
Since the frequency of the output signal is _IF + _T + _d , the frequency of the two video signals I and Q is equal to the frequency difference _d between the two signals. That is, regardless of whether the target is stationary ( _T = 0) or moving ( _T ≠ 0), in the radar device of the present invention, the Doppler frequency of the output signal of the video amplifier 10 of the receiver 21 is always matches the Doppler frequency _d due to antenna movement and is independent of _T , so the angular resolution can be improved in the same way as when observing a stationary target with conventional equipment.

〔Effect of the invention〕

As described above, according to the radar device according to the present invention, by using the newly installed fixed antenna and the output of the receiver connected thereto as a local signal for phase detection of the receiver on the mobile antenna side,
Synthetic aperture methods can be used to improve angular resolution regardless of whether the target is stationary or moving.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a radar device according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a conventional radar device that uses the Doppler effect by moving an antenna, and FIG. 3 is a synthetic aperture. It is a diagram for explaining the principle of the law. 1 is a mobile antenna, 2 is a fixed antenna, 3 is a transmitter/receiver switch, 4 is an RF amplifier, 5 is a mixer, and 6 is a
IF amplifier, 7 is AGC, 8 is PSD, 9 is π/2 phase shifter, 10 is video amplifier, 11 is STALO, 1
2 is COHO, 13 is a transmitter, 14 is an antenna drive device, 15 is an A/D, 16 is an input buffer memory, 17 is an FFT, 18 is a square law detection means, 19 is an output buffer memory, 20 is a display, 21, 23
is a receiver, and 22 is a signal processing device. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A mobile antenna unit driven by an antenna driving means, a first receiver connected to the mobile antenna and amplifying and detecting a high frequency signal received by the mobile antenna, and A signal processing device comprising an A/D conversion means for converting a phase-detected signal into digital data, and a fast Fourier transform means for Fourier transforming the digital data, and a Doppler effect produced by moving the antenna. In a radar device that obtains an angular resolution higher than the angular resolution determined by the aperture of an actual antenna using and a second receiver using the second receiver.
The output of the intermediate frequency amplifier of the receiver is used as a local signal of the phase detector of the first receiver, and the fluctuation component of the Doppler frequency due to the movement of the target is removed from the received signal of the first receiver. radar equipment.