JPH042913B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active sonar device using FM signals.

(Prior Art) This type of sonar device transmits a pulsed sound wave (FM signal) whose frequency is swept with a predetermined frequency deviation width into the water, and receives a received signal by receiving the sound wave reflected by an underwater object. arise. Sonar devices that transmit FM signals and detect reflected sounds from targets have traditionally used a method to improve the signal-to-noise ratio called detection pulse compression. Regarding the conventional method, Figures 2 to 4
This will be explained with reference to the figures. In this method, the transmission pulse width is divided into N equal parts, and the second
Different frequencies ( ₁ , ₁ + △, ₁ + 2 △...) are assigned in steps of △ as shown in the figure, and the frequency of the transmitted pulse is modulated in steps to emit a pulse waveform as shown in Figure 3 ( 2 to 4 show examples in which the number of divided channels N is 8, the transmission pulse width is 8ΔT, and the frequency shift width is 7Δ).
In this conventional system, the received signal is processed by the circuit shown in FIG. The received signal 101 is passed through the splitter 2 (filter 2
Each demultiplexed signal becomes an envelope detection signal by the detector 3 (consisting of diodes 31 to 38), and is delayed when it passes through the delay device 4 (consisting of delay circuits 41 to 47). The output of device 4 has a pulse width equal to △T and a frequency of ₁ , ₁ + △..., ₁ +, respectively, at exactly the same time.
A signal obtained by detecting a signal of 7△ appears. Output signal 1 obtained by pulse-compressing input signal 101 by adding the output signal of delay device 4 in adder 5
05 is obtained. In this conventional sonar device, since N signal components are added, the gain GS for the signal is GS=20logN. Also, the gain GN against noise is GN=10log1/N+20logN=10logN.

Therefore, it is well known that the signal processing gain PG is PG=GS-GN=10logN.

(Problem to be Solved by the Invention) However, the target of a sonar device is often moving, and in such cases, the signal processing gain PG described above is significantly reduced due to the target echo frequency shift due to the Doppler effect. It will deteriorate.

As an example, transmission frequency is 50KHz, transmission frequency deviation is ±400Hz (step frequency △=100Hz), N=
8 will be explained with reference to FIG. FIG. 5 is a diagram showing the receiving frequency bands, where Ba shows the band of the received signal of a stationary target, and B _b1 and B _b2 show the bands of the received signal of the moving target of 15 knots and 23 knots, respectively. In this figure, as in FIGS. 2 to 4, the receivable band is ₁ to ₁ +7Δf. Therefore, the entire band of Ba falls within the receivable band, half of the band of B _b1 falls within the receivable band, and B _b2 does not fall within the receivable band at all (in this figure, the part of Ba that falls within the receivable band, B _b1
(are shown with diagonal lines). Therefore, the signal processing gain PG for a stationary target is PG=10iog8=9 dB, but for a target with a speed of 15 knots, PG=0 dB, and reception is impossible for a target with a speed of 23 knots.

As described above, the conventional sonar apparatus has the disadvantage that the signal processing gain fluctuates significantly depending on the relative speed to the target, and it is not possible to receive echoes of a moving target at a speed higher than a certain speed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a sonar device that can obtain a high signal processing gain even for signals received from a moving target.

(Means for Solving the Problems) A sonar device according to the present invention includes a means for transmitting a pulsed sound wave whose frequency is swept with a predetermined frequency deviation width into water, and a means for transmitting the sound wave reflected by the underwater object. means for generating a received signal; a branching filter that divides the received signal into a plurality of frequency components; a detector that detects each of the frequency components and generates a detected signal; and a plurality of devices that delay and add each of the plurality of detected signals. It consists of a delay adder and a selector that selects the maximum output from these delay adders,
The total bandwidth of the duplexer is wider than the frequency shift width, and the plurality of detected signals delayed and added by the delay adder are signals obtained by detecting a plurality of frequency components within a predetermined band, and The band is characterized in that each corresponding delay adder has a different band.

(Operation) In the present invention, the total bandwidth of the duplexer is made wider than the frequency shift width of the transmitted sound wave in consideration of the Doppler frequency shift of the received signal caused by the movement of the target. There are multiple delay adders. The detected signals received by these delay adders are signals obtained by detecting a plurality of frequency components within a predetermined band. Further, the predetermined band is different for each delay adder through which frequency components within the predetermined band are detected and guided. Therefore, the frequency bands of the received signals added by each delay adder are different, and even if the target is moving and the received signal undergoes a Doppler frequency shift, one of the delay adders will not be able to generate a pulse compression signal of sufficient level. Can be output. Then, the selector selects the largest one among the outputs (pulse compression signals) of the delay adder. Therefore, by using the output signal of this selector, the same signal processing gain can be obtained for the received signal of a moving target as for a stationary target.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a receiving system diagram of an embodiment of the present invention. In this embodiment, the received signal 101 is applied to the duplexer 21, and the duplexer 21 receives the signal including the Doppler shift _D caused by the movement of the target _.
It has a sufficient number of channels to cover the frequency bands shown below. In this example, for convenience of explanation, there are 24 channels, and the total bandwidth of the duplexer 21 is 23Δ, which is wider than the frequency shift width of 7Δ of the transmitted sound wave. Each output of the 24 channels is converted into envelope detection signals 301 to 324 by the detector 31. These envelope detection signals 301-324 are applied to delay devices 401-417 having the same delay time configuration as delay device 4 in FIG. 4, eight signals at a time. The outputs of the delay devices 401 to 417 are sent to an adder 50 provided for each delay device.
1 to 517, and pulse compression is performed for each bandwidth. In this way, compressed pulse signals 501a to 517a can be obtained simultaneously over the entire reception band. The selector 6 selects the adder that outputs the maximum level pulse compression signal (one of 501a to 517a), and sets the pulse compression signal as the output signal 106. Since the output signal 106 is a compressed pulse signal without signal processing gain deterioration and the selected adder is compatible with Doppler shift, the target Doppler frequency can be detected.

As described above, in this embodiment, by arranging branching filters over the entire reception band and arranging eight delay-adding adders for each frequency △, the signal due to the Doppler shift of the target reception signal is It is possible to significantly improve the deterioration of processing gain and also provide a function of estimating the target speed from the Doppler component of the target.

(Effects of the Invention) According to the present invention, as described above in detail, a sonar device that can obtain a high signal processing gain even for a received signal of a moving target can be provided.

[Brief explanation of drawings]

Fig. 1 is a receiving system diagram of an embodiment of the present invention;
Figure 3 shows the relationship between time and frequency in the FM transmission pulse, Figure 3 shows the frequency structure of the FM transmission pulse, Figure 4 shows the reception system in a conventional sonar device using FM signals, FIG. 5 is an explanatory diagram showing the influence of Doppler shift in the frequency band of the received signal. 2... splitter, 3... detector, 4... delay device,
5...adder, 6...selector, 21...brancher,
31...Detector, 401-417...Delay device, 5
01-517...Adder.

Claims (1)

[Claims] 1 means for transmitting a pulsed sound wave whose frequency is swept with a predetermined frequency deviation width into water; means for receiving the sound wave reflected by the underwater object and generating a received signal; a detector that detects each of the frequency components and generates a detected signal; a plurality of delay adders that delay and add each of the plurality of detected signals; and a selector for selecting a signal, the total frequency bandwidth of the demultiplexer is wider than the predetermined frequency deviation width, and the frequency bandwidth of the plurality of detected signals delayed and added by the one delay adder is The frequency bands of the detected signals, which are equal to the predetermined frequency deviation width and are delayed and added by the plurality of delay adders, are shifted from each other by a band corresponding to one duplexer, and the plurality of delay adders are provided. By that,
A sonar device characterized by realizing delay addition of the entire frequency bandwidth.