JPS6216694Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a radar receiving device, and particularly to a pulse radar device that emits a high-frequency pulse signal into space from an antenna and receives a reflected signal from a radar search space. The present invention relates to a receiving device useful for suppressing erroneous detection of unnecessary received signals.

In addition to the target signal, radar received signals include unnecessary received signals (e.g. reflected received signals from the earth, mountains, etc., reflected received signals from the sea surface, reflected received signals from rain clouds, etc.; hereinafter, these unnecessary received signals are These clutter signals may make it impossible to detect the target signal, or the clutter signal may be mistakenly detected as a target signal other than the target signal. For this reason, radar devices have conventionally adopted various techniques to remove or reduce clutter signals. Typical examples include a moving target indicator (hereinafter referred to as an MTI device) and a CFAR receiver (hereinafter referred to as an MTI device). Constant False
Alarm Rate Receivers (hereinafter referred to as CFAR receivers) are well known (for example, Merrill I.
Skolnik“RADAR HAND BOOK”Chapter
17, MTI Radar and Section 5.8, CFAR
(See Considerations). MTI equipment is a device that removes reflected received signals from the ground, mountains, buildings, etc. (hereinafter referred to as fixed clutter signals) and detects reflected received signals from aircraft, ships, etc., and is used in conventional pulse radar equipment. MTI devices that have been developed, especially coherent MTI devices, have remarkable clutter signal removal performance for clutter signals other than fixed clutter signals (e.g., sea surface clutter signals, rain cloud clutter signals, etc., hereinafter referred to as moving clutter signals). It has no drawbacks. On the other hand, CFAR receivers, especially CFAR receivers using logarithmic amplifiers (hereinafter referred to as logarithmic CFAR receivers), have the ability to reduce moving clutter received signals to near the receiver noise level (for example, J.Croney
“Clutter on Radar Displays”Wireless
Engineer pp83-96, April, 1956). Therefore, a radar receiving device that effectively eliminates or reduces clutter signals by using a combination of an MTI device and a logarithmic CFAR receiving device has been proposed and put into practical use. However, this type of radar receiver is difficult to use because the logarithmic amplifier used has the lower limit of its logarithmic characteristic range to a point below the receiver noise level (e.g., approximately below the receiver noise level).
As shown in Figure 1, the fixed clutter signal component removed by the MTI device to a point below the receiver noise level is logarithmically
On the contrary, when the signal passes through the CFAR receiver, it is amplified to near the receiver noise level, which has the disadvantage that signals remaining from fixed clutter may be erroneously detected. Below, one specific example will be given to further explain the drawbacks of this type of conventional receiving device.

First, FIG. 2 shows an example of the configuration of a conventional receiver. 1 is the input of the MTI receiver circuit 2,
An intermediate frequency reception signal as shown in FIG. 1a is input. The output signal 3 of the MTI reception circuit 2 is input to the logarithmic CFAR reception circuit 4. The signal 3 is
The output signal of the MTI device is a signal in which the fixed clutter signal as shown in FIG. 1b has been removed to below the receiver noise level. In the figure, A' indicates the fixed clutter remaining signal, C' indicates the rain cloud clutter remaining signal, D indicates the target signal, and E indicates the target detection level. The input signal of the logarithmic CFAR receiving circuit 4 is connected to a logarithmic amplifier 5, and the signal amplitude is increased by 3.
The signal is converted to have a logarithmic characteristic as shown in the figure. In the figure, A is the fixed clutter residual signal,
B indicates receiver noise, and C indicates the remaining signal after the rain cloud clutter has disappeared. Also, G indicates the logarithmic characteristic range. By such conversion, the amplitude of the changing component of the clutter signal at the output of the logarithmic amplifier 5 becomes approximately the same level as the amplitude of the changing component of the receiver noise. The output signal of the logarithmic amplifier 5 becomes the input of the average value detector 6 and the signal delayer 7. The average value detector 6 detects the average value (or DC component) of the input signal. The signal delayer 7 gives the input signal a delay time that matches the signal delay time generated by the average value detector 6. The subtractor 8 subtracts the output signal of the average value detector 6 from the output signal of the signal delayer 7. By such circuit operation, the average value (or DC component) is removed from the input signal, and
As a result, the clutter signal is at approximately the same level as the receiver noise level. The output signal of the subtractor 8 is converted back to a linear signal by the antilogarithmic amplifier 9, and then converted to a logarithmic signal.
This is the output of the CFAR receiving circuit 4 (FIG. 1C). In the figure, F indicates a cluster signal that is erroneously detected.

As is clear from the above explanation, conventional receivers have excellent clutter signal suppression performance that suppresses clutter signals that are larger than the receiver noise level to the receiver noise level. It also raises small clutter signals (mainly fixed clutter residual signal A′) to the receiver noise level (A″ indicates the enhanced fixed clutter residual signal, C″ indicates the suppressed rain cloud clutter signal). This method has the disadvantage of intensifying small clutter signal levels.

The present invention proposes that when suppressing and removing clutter signals in a radar receiver that uses a combination of such an MTI device and a logarithmic CFAR receiver, in addition to the signal system that performs logarithmic CFAR reception processing on the output signal of the MTI device. Radar reception with excellent clutter signal suppression and removal performance that eliminates the above drawbacks by adding a signal system that does not undergo logarithmic CFAR reception processing and optimally selecting the output signals of these two signal systems as the receiver output signal. It provides equipment.

According to the present invention, a radar signal whose fixed clutter component has been suppressed through signal processing is received, and a logarithmic CFAR (Constant False Alarm) is applied to this signal.
a logarithmic CFAR circuit that performs time-division selection and output of the radar signal and the output signal of the logarithmic CFAR circuit; a signal obtained after the signal processing of the reflected signal from a predetermined region of the search space; an average value circuit that calculates the average value of signals related to the signal and outputs the average value signal; a reference level generation circuit that outputs a reference level signal corresponding to the receiver noise level; the average value signal is larger than the reference level signal. and a comparison circuit that generates a control signal that controls the selection circuit to output the output signal of the logarithmic CFAR circuit and output the radar signal when the output signal is small. It will be done.

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 4 is an example of a configuration diagram of a radar receiving device based on the present invention, showing an input terminal 10, a logarithmic CFAR receiving circuit 11, an output signal of this logarithmic CFAR receiving circuit 11, and an input from the input terminal 10. a signal selection circuit 17 that selectively switches between signals and outputs the signal to the output terminal 23; and a selection control signal generator that generates a control signal for controlling which signal the signal selection circuit 17 selects and outputs. circuit 20
Contains.

The logarithmic amplifier 12, average value detector 13, signal delay unit 14, subtractor 15, and antilogarithm amplifier 16 that constitute the logarithmic CFAR receiving circuit 11 are those used in the conventional logarithmic CFAR receiving circuit shown in FIG. is exactly the same. The signal selection circuit 17 is composed of a signal delayer 18 and a selector 19, and the selection control signal generation circuit 20 is composed of a reference level signal generator 21 and a comparator 22.

The radar reception signal input to the input terminal 10 is subjected to logarithmic CFAR processing by the logarithmic CFAR receiving circuit 11, and its output signal is input to the signal selection circuit 17. The logarithmic CFAR processing operation is exactly the same as the conventional logarithmic CFAR processing operation described in the example of FIG. The other input of the signal selection circuit 17 receives the radar reception signal that has not been subjected to logarithmic CFAR processing and is input to the input terminal 10 , and is time-delayed by the signal delay device 18 . That is, the same delay time as the signal delay time generated in the logarithmic CFAR receiving circuit 11 is provided by the signal delay device 18.

The two input signals input to the signal selection circuit 17 are time-divisionally selected by the selector 19 and become one output signal, which is output to the output terminal 23. Which of the two input signals is output from the selector 19 is determined by a control signal from the selection control signal generation circuit 20. The selection control signal generation circuit 20 is
For a received signal whose level is higher than the receiver noise level among the radar received signals inputted to the input terminal 10, the output signal of the logarithmic CFAR receiving circuit 11 is outputted from the signal selection circuit 17, and the radar received signal is Generates a selection control signal such that the signal input to the input terminal 10 (signal that has not been subjected to logarithmic CFAR processing) is output from the signal selection circuit 17 for a received signal whose level is lower than the receiver noise level. do. Detection of a received signal having a level greater (or less) than the receiver noise level is performed by the following circuit operation. Average value detector 13 which is one of the constituent circuits of logarithmic CFAR receiving circuit 11
The average value (or DC component) of the input received signal is detected. The output signal of this average value detector 13 becomes the input of the selection control signal generation circuit 20,
Connected to comparator 22. The output signal of the reference level signal generator 21 is connected to the other input of the comparator 22. Since the reference level signal generator 21 generates a reference signal with a level equivalent to the average value (or DC component) of the receiver noise, the average value detector 13
By comparing the output signal of the reference level signal generator 21 with the output signal of the reference level signal generator 21 by the comparator 22, a received signal having a level higher (or lower) than the receiver noise level is detected. The reference level signal generator 21 can generate a reference level signal in a preset manner, or can generate a reference level signal by extracting the average level of receiver noise from the output signal of the average value detector 13. is also possible.

Furthermore, as is clear from the above examples, the logarithm
The radar signal input to the CFAR circuit 11 is not limited to the MTI output, and the present invention can be similarly applied to any signal whose fixed clutter has been suppressed by other signal processing. Further, the average value signal to the comparison circuit 22 in the selection control signal generation circuit 20 is the one for the output of the logarithmic amplifier 12 of the logarithmic CFAR circuit, but the average value signal of the radar signal in which fixed clutter has been suppressed is used. It is obvious that it is also good. In this case, the reference level output from the reference level signal generator 21 may be determined in advance accordingly.

This circuit operation provides the advantage that the received signal (mainly the residual signal of fixed clutter) that is lower than the receiver noise level is outputted to the output terminal 23 at a level lower than the receiver noise level. .

As explained above, the present invention includes a logarithmic CFAR receiving circuit that performs logarithmic CFAR processing on a radar received signal, a signal selection circuit that time-divisionally selects and outputs an input radar received signal and an output signal of the logarithmic CFAR receiving circuit, and a signal selection circuit that controls signal selection. By configuring a logarithmic CFAR receiver with a selection control signal generation circuit that generates a control signal to suppress the clutter signal, the clutter signal, which is at a level higher than the receiver noise level, is suppressed to near the receiver noise level and output. This has the effect of outputting the clutter signal, which is at a level lower than the noise level, at a level lower than the receiver noise level.

[Brief explanation of the drawing]

Figure 1 is a signal waveform diagram of each part of a conventional receiving device.
FIG. 2 is a block diagram showing a specific example of a conventional receiving device, and FIG. 3 is a characteristic diagram showing the logarithmic characteristics of a logarithmic amplifier. FIG. 4 is a block diagram of a radar receiving device shown as an embodiment of the present invention. . 1...Input signal, 2...MTI receiving circuit, 3...
...output signal, 4,11...logarithmic CFAR receiver circuit,
5, 12... Logarithmic amplifier, 6, 13... Average value detector, 7, 14... Signal delay device, 8, 15... Subtractor, 9, 16... Anti-logarithmic amplifier, 10... Input terminal, 17...Signal selection circuit, 18...Signal delay device, 19...Selector, 20...Selection control signal generation circuit, 21...Reference level signal generator, 22...
Comparator.

Claims (1)

[Scope of utility model registration request] A radar signal whose fixed clutter component has been suppressed through signal processing is received, and logarithmic CFAR is applied to this signal.
(Constant False Alarm Rate) Logarithm to process
CFAR circuit; the radar signal and the logarithmic CFAR;
a selection circuit that time-divisionally selects and outputs the output signal of the circuit; an average value circuit that calculates an average value related to the signal obtained after the signal processing of the reflected signal from a predetermined area of the search space and outputs an average value signal; a reference level generation circuit that outputs a reference level signal corresponding to a receiver noise level;
A radar receiving device comprising: a comparison circuit that outputs an output signal of a CFAR circuit and generates a control signal that controls the selection circuit to output the radar signal when the output signal is small.