JPS6247099Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a pulsed Doppler radar device that switches and transmits transmission pulses having different repetition periods.

Normally, in a pulsed Doppler radar system, a Doppler filter removes clutter from a fixed target or leakage power from transmitted pulses, and extracts the reflected signal (echo) from a moving target. The band is approximately determined by the speed of the object identified as a moving target. Therefore, in order to prevent velocity blind from occurring within this Doppler frequency range, the repetition frequency (hereinafter abbreviated as PRF) of the transmission pulse cannot be made smaller than this Doppler frequency. For example 10G
If a 2-matsuha target is to be detected with a Hz transmit frequency pulse without velocity blinding, the Doppler frequency is approximately 46 kHz, and the PRF must be greater than 46 kHz. This situation is shown in Figure 1. Figure a shows the transmitted pulse of period T with time t on the horizontal axis, and in Figure b with frequency on the horizontal axis, the shaded SP ₁ is the reflection spectrum from a fixed target, and ₀ is the center. It is the frequency. SP ₂ is the reflection spectrum from a moving target. d is the Doppler frequency. W indicates the band of the Doppler filter, and is shown for the case where it is configured with a sideband filter, but it may also be configured as shown in c in the same figure. In either case, a zero Doppler removal filter may be inserted.

However, there is an inherent disadvantage in a pulsed Doppler radar device having a transmitted pulse having a relatively high PRF. In other words, a pulsed Doppler radar device that has a high PRF transmission pulse and has excellent clutter suppression performance has blindness with respect to distance. That is, in the example above
For PRF46kHz transmission pulse, distance (X) = 10 ⁶ × 150 [μs] / 46 × 10 ³
[kHz] = 3.26 [Km] In other words, there is a pulse to be transmitted at each point approximately every 3.3 km, and distance information becomes blind at this point. Therefore, in order to detect a target at a longer distance than this distance with this pulse Doppler radar device, it is necessary to take measures to avoid this point. A possible means for this is to prepare a plurality of transmission pulses with different PRFs and to switch between these transmission pulses for use. That is, as shown in FIG. 2, when the reflected signal E from the moving target approaches the currently transmitted transmission pulse _P1 , the transmission pulse is switched to the transmission pulse _P2 . In other words, the position of the transmitted pulse is shifted to before or away from the reflected signal E.

However, another problem arises at this time. In other words, this is the velocity blind restriction on the Doppler frequency d described above. Both transmission pulses before and after switching
If there is a restriction that there should be no speed blind on P ₁ and P ₂ and if the Doppler filter W shown in Fig. 1c is normally a fixed filter, then the Doppler filters W on both side bands should be as shown in Fig. 3a. As shown in Figure 1a, there are points (filter blind points) where Doppler cannot be detected on the equivalent Doppler filter W' because they function equivalently as a filter as shown in Figure 1a.
We must ensure that there are no That is, the third
Figure a shows the state before the transmission pulse is switched, and if the transmission pulse is switched to a higher PRF transmission pulse as shown in Figure b, a filter blind point B may occur. Due to the above two constraints, the range of PRFs of transmission pulses that can normally be selected is limited. This kind of problem is not a problem if the Doppler filter has a narrow band and the filter can be tuned electrically to track the Doppler frequency, but the narrow band and electrical tuning of this filter is technically difficult. Since this is difficult, methods are usually used in which fixed narrowband filter banks are arranged or the local oscillator frequency is tuned. In any case, using a fixed Doppler filter that covers the Doppler frequency range simplifies the radar system.
For example, even if the receiver series shown in FIGS. 5 and 8, which will be explained later, are configured as multiple channels to configure a monopulse receiver, it will be much simpler than configuring one receiver sequence as multiple channels. There are advantages.

Now, if the selection range of PRF is limited,
Transmission pulses must be switched effectively. In other words, the problem is when to switch the transmission pulses.

Below, we will briefly explain a conventional example of a pulsed Doppler radar device that switches and transmits two transmission pulses P ₁ and P _2. First, which transmission pulses P ₁ and P ₂ are used to use the two PRF sequences? This is because it is easy for the determining means to obtain an output that selects between the two. Then, depending on the transmission pulses P ₁ and P ₂ and the position of the distance gate, the determination means determines whether after reflection of either of the transmission pulses P ₁ or P ₂ ,
The decision is made based on whether the distance gate to the target is farther away, or it is decided to switch when it enters a certain range, so systems that choose between the two are processed with relatively simple calculations. can. FIG. 4 shows an example of switching between two transmission pulses P ₁ and P _2. Which of the transmission pulses P ₁ and P ₂ is farther from the reflected signal from the moving target, that is, the time difference between the two transmission pulses and the reflected signal is Depends on whether it is larger. For example, when there are reflected signals at the two points Z ₁ and _Z in Figure 4, using the transmission pulse P ₂ will result in clutter C of the transmission pulse P ₂ .
Since the reflected signal cannot be detected due to this, in such a case, the transmission pulse is switched to the transmission pulse _P1 . Also, it is conceivable to use three or more transmission pulses, but if we use the simple method described above as a determination method, the determination that "any one is fine" for the remaining two or more Therefore, it is difficult to obtain an effect even though the degree of freedom is large.

FIG. 5 shows a conventional example of a pulsed Doppler radar device that uses two systems of transmission pulses P ₁ and P ₂ . Repetitive signals S ₁ , S ₂ from PRF generator 11
is applied to gate converter 12. This gate converter 12 further includes a zero distance trigger TP (Fig. 6a).
) and a distance gate G (see FIG. 6b) are provided. The range gate G is usually sent from a range tracker (not shown) without a range blind. That is, it is not a signal with a high PRF such as the transmission pulses P ₁ and P ₂ , but a gate of another low PRF trigger series, and there is no other pulse within the time from the distance 0 trigger TP to the distance gate G. Time indicates distance. Therefore high PRF
A gate converter 12 converts the gate into a signal.
is the determined reference value T ₀ of the high PRFF signal (Fig. 6c
This is a converter that divides the distance gate G by the distance gate G (see Fig. 6d) and delays the high PRF gate (see Fig. 6d) by the remainder time t. Therefore, the transmission pulse
The repetitive signals S ₁ and S ₂ corresponding to P ₁ and P ₂ are subjected to the above-described action by the gate converter 12, and are converted into gate signals, respectively, and sent to the PRF selection determiner 1.
3 and the PRF selector 14, the PRF selection determiner 13 detects the transmission pulse P ₁ (or transmission pulse P ₂ ) during transmission, the corresponding repetition signal S ₁ (or repetition signal S ₂ ), or the transmission output. The repeat signal is determined by comparing the distance between the signal and the repeat signal S ₂ (or repeat signal S ₁ ) corresponding to the untransmitted transmission pulse P ₂ (or transmission pulse P ₁ ).
A determination signal J for selecting either S ₁ or the repetition signal S ₂ is supplied to the PRF switchers 14 and 16. Of course, the gated repetitive signal S ₁ ,
S ₂ will move accordingly if the target moves. The PRF switchers 14 and 15 switch and select the repetitive signals S ₁ and S ₂ in accordance with the determination signal J.

However, in the case of such a configuration, suppose that the range of 40 km is around the Doppler frequency of 46 kHz as in the previous example.
If an attempt is made to switch and detect the two transmission pulses P ₁ and P ₂ having PRF, the following problem occurs. That is, assuming that the PRF of the transmission pulse P ₁ is 46 kHz (distance equivalent 3.26 Km) and the PRF of the transmission pulse P ₂ is x kHz (distance equivalent y Km), it is desirable that these two are multiples of integers. In other words, 3.26×13=42.38Km...(1) y×14=42.38Km...(2) From equations (1) and (2), y=3.03Km and x=49.6kHz.
PRF46kHz pulse interval (period) 21.7μs,
The pulse interval (period) of PRF49.6kHz is 20.16μs. When these two series of transmission pulses P ₁ and P 2 having PRFs of 46 kHz and 49.6 kHz are switched and used, as shown in Fig. 7, the first blind point of _{the transmission pulse P 1 is} approximately 1.5 μs after switching, and the second blind point is approximately 1.5 μs after switching. Approximately 3.0μs after switching at point, below n(21.7−20.16)
A separation of μs will be obtained. Normally, it is desirable that the separation caused by this switching be large in order to avoid the clutter distribution C immediately after the transmission of the transmission pulses P ₁ and P ₂ as much as possible, but if it is too large, it will cause blindness within the given distance range as described above. of a series that does not cause
It becomes difficult to select a PRF. For this reason, for example, if the reception power of the clutter C immediately after transmission is large and a separation of at least 5 μs is desired, this can be achieved by using the transmission pulse P ₁ of 46 kHz as shown in Figure 7. After the fourth pulse, that is, when the target is located at a distance of 3.26×4≒13 km or more, some kind of countermeasure must be taken in a range closer than 13 km.

This idea was made to deal with the above situation, so when selecting and using transmission pulses with three or more types of repetition periods, it is possible to use a very simple circuit configuration.
It is an object of the present invention to provide a pulsed Doppler radar device that can reduce the influence of clutter near a distance blind point.

Hereinafter, one embodiment of this invention will be described in detail with reference to the drawings. First, in FIG. 8, a stabilizing oscillator (STALO) 21 and a pulse modulator 36 to be described later are shown.
The output signal is supplied to a transmission amplifier 22, and the output signal of this transmission amplifier 22 is radiated into space as a transmission pulse via a duplexer 23 and an antenna 24 in sequence. The reflected signal from the target object is supplied to a mixer 25 via an antenna 24 and a transmission/reception switch 23 in this order. The mixer 25 receives the output signal of the stabilizing oscillation circuit 21 and converts the reflected signal supplied from the transmitter/receiver switch 23 into an intermediate frequency. This intermediate frequency signal is sent to intermediate frequency amplifier 2.
6 to the transmission pulse suppressor 27.
The transmission pulse suppressor 27 receives an output signal from a gate generator 35, which will be described later, and suppresses fixed target clutter or leakage power of the transmission pulse at this timing. The output signal of this transmission pulse suppressor 27 is supplied to an amplifier 28. This amplifier 28
receives an output signal from a gate generator 43, which will be described later,
The amplification operation is performed at this timing. amplifier 2
The output signal of 8 is supplied to a Doppler filter 29,
This Doppler filter 29 extracts only Doppler frequency components from the moving target. The output signal of this Doppler filter 29 is supplied to a detector 31 via a signal processing circuit 30. Next, the features of this invention will be explained. First, in this example, three types of transmission pulses with different repetition periods are used.
It transmits by switching P ₁ , P ₂ , P ₃ , and the PRF of each transmission pulse P ₁ , P ₂ , P _{3 is 1} ,
₂ , ₃ . In the figure, numeral 32 is _a PRF generator, _which generates _{PRF 1 , 2} ,
A repetitive signal S ₁ with a frequency corresponding to ₃ ,
Generate and derive S ₂ and S ₃ . The repetitive signals S ₁ , S ₂ , S ₃ which are the output signals of the PRF generator 32 are supplied to the gate converter 37, and the repetitive signal S ₁ is
The repeat signal is supplied to PRF switch A34.
S ₂ and S ₃ are selectively switched by the PRF switch B33 and then supplied to the PRF switch A34. The gate converter 37 is further supplied with a distance zero trigger TP and a distance gate G from a distance tracker (not shown). This gate converter 37
operates similarly to the gate converter 12 described in FIG. 5, and converts the repetitive signals S ₁ , S ₂ , and S ₃ into gate signals, respectively. Among the repetitive signals S ₁ , S ₂ , and S ₃ converted into gate signals by the gate converter 37 , the repetitive signal S ₁ is supplied to the PRF selection determiner 41 . On the other hand, the repetitive signals S ₂ and S ₃ are transmitted to the PRF switch B3.
After being selectively switched by 8, the PRF switch B38 is supplied to the PRF selection determiner 41.
The switching operation is performed by the PRF selector 40. That is, the PRF selector 40 is supplied with the distance zero trigger TP and the distance gate G, and the switching distance setter 3 is set with the distance information to the target indicated by the distance gate G and the switching distance as the distance condition.
9, select which of the repeated signals S ₂ and S ₃ is more advantageous, and select the more advantageous one as PRF.
It is output to the switch B38. Note that the output signal of the PRF selector 40 is also supplied to the PRF switch B33, and thereby the PRF switch B33 supplies the more advantageous one of the repetitive signals S ₂ and S ₃ to the PRF switch A34. The PRF selection determiner 41 receives the repetitive signal S ₁ from the gate converter 37 and the PRF selector B38.
Repeated signal S ₂ (or repeated signal S ₃ )
is supplied, and the distance gate G is also supplied. Assuming that the repetition signal S ₁ and the repetition signal S ₂ are supplied, the PRF selection determiner 41 generates a determination signal J for selecting either of the repetition signals S ₁ and S ₂ according to the distance gate G. PRF
Supplied to switch A34, 42. PRF switch A
42 is a repetitive signal S ₁ from the gate converter 37.
However, the repeating signal S ₂ (or repeating signal S ₃ ) is supplied from the PRF switch B38, and the above-mentioned
Depending on the determination signal J from the PRF selection determiner 41, one of the repetition signal S ₁ and the repetition signal S ₂ (or repetition signal S ₃ ) is selected and supplied to the gate generator 43 . This causes the gate generator 43 to turn on the distance gate amplifier 28.

On the other hand, the PRF switch A34 switches between the repeat signal S ₁ and the repeat signal S ₂ (repetitive signal
S ₃ ) is selected and supplied to the gate generator 35. The output signal of the gate generator 35 is supplied to a pulse modulator 36 and also to the transmission pulse suppressor 27. The output of the pulse modulator 36 is supplied to the transmit amplifier 22.

FIG. 9 shows the switching states of the transmission pulses P ₁ , P ₂ , P ₃ . Figure a shows the zero distance trigger TP, and Figures b, c, and d show the transmission pulses P ₁ , P ₂ , and P 3 respectively. ₃ ,
Figure e shows the switching distance l of the switching distance setting device 39 (see FIG. 8). In the section from distance 0 to l ₁ , separation is achieved by switching transmission pulses P ₁ , P ₂ , P ₃ , that is, transmission pulses P ₁ and P ₂ , P ₁
Since _the time difference between the transmission pulses P 1 and P ₃ is larger, the transmission pulses P ₁ and _{P 3 are} selected in this section, and switching between these pulses P ₁ and P ₃ is performed. distance
In the interval from l ₁ to l ₂ , the transmitted pulses P ₁ , P ₂ , P ₃
Separation by switching is the transmission pulse P ₁ , P ₂
is larger, so in this interval, the transmitted pulse
P ₁ and P ₂ are selected, and these pulses P ₁ and P ₂ are switched. At distance l ₂ or more, the transmitted pulses P ₁ , P ₂ ,
Separation by switching _P3 is the transmission pulse
Since P ₁ and P ₃ are larger, the transmission pulses P ₁ and P ₃ are selected in this section, and switching between these pulses P ₁ and P ₃ is performed.

This embodiment described in detail above has the following effects. First, to summarize the transmission pulse switching procedure that is a feature of this embodiment, one of three types of repetitive signals S ₁ , S ₂ , and S ₃ having different repetition periods is selected.
Let the repeated signal S be _{a 1} reference signal. remaining 2
Distance information of a moving target (for example, distance gate information from a distance tracker) from among the two repeated signals S ₂ and S ₃
The repeated signal S ₂ which has a larger time difference from the repeated signal S ₁ for each preset distance segment including
(or the repeated signal S ₃ ) and combine it with the reference repeated signal S ₁ . In other words, one reference repetitive signal S ₁ is determined, and the remaining two repetitive signals S ₂ and S ₃ are switched according to the distance information and combined with the repetitive signal S ₁ to create a combination of the two, that is, the repetitive signal S ₁ and Set the combination of S ₂ and the combination of repeating signals S ₁ and S ₃ and switch them. The combination obtained in this way according to the distance information, repeats the one with the larger time difference with the reflected signal from among the repeated signals S ₁ and S ₂ (or repeated signals S ₁ and S ₃ ), similar to the switching example in FIG. 4. The signal is selected and switched, and a transmission pulse corresponding to the selected repetition signal is transmitted.

In this way, since the paths for selecting the optimal repetitive signal from among the three types of repetitive signals S ₁ , S ₂ , and S ₃ are all alternative paths, the advantage is that the circuit configuration is extremely simple. be. Furthermore, if the repetition period and distance conditions of the repetition signals S ₁ , S ₂ , and S ₃ are appropriately selected, two types of repetition signals corresponding to the combination of the two types of repetition signals selected over all the sections detected by the pulse Doppler radar device can be obtained. Sufficient separation can be achieved by switching the types of transmission pulses. Therefore, the effect of clutter near the distance blind point can be almost eliminated. Furthermore, the constraint that the above-mentioned integer is a multiple between two types of repeated signals in one combination holds true even if it does not hold over the entire range detected by the pulsed Doppler radar device (for example, in the previous example, a certain combination (The above constraints only need to hold within 13 km, not 40 km.) This has the advantage that it is relatively easy to select the repetition period to obtain sufficient separation.

It should be noted that this invention is not limited to the previous embodiment and can be implemented in other ways. For example, the repetitive signals S ₂ and S ₃ in the previous embodiment are generated and derived from one separately prepared variable PRF generator, and the output signal of the PRF selector 40 is supplied to generate the repetitive signals S ₂ and
You can also switch to _S3 . Further, in the previous embodiment, a case was explained in which three types of repetitive signals having different repetition periods were used, but it goes without saying that the present invention can also be implemented using four or more types of repetitive signals. In addition, various other configurations can be considered in which one combination of two types of repetitive signals is selected from among three or more types of repetitive signals having different repetition periods.

In this way, according to this invention, at least three types of repeating signals with different repeating periods are selected by an alternative processing format based on distance information and preset distance conditions, and the most optimal one is selected. It is possible to provide a pulsed Doppler radar device that has a simple circuit configuration, can reduce the influence of clutter in the vicinity of a distance blind point, and can easily set a repetition period, since it is configured to obtain transmission pulses having a repetition period. can.

[Brief explanation of the drawing]

Figures 1a, b, and c are signal waveform diagrams for explaining the Doppler filter; Figures 2a and b are signal waveform diagrams for explaining switching between two transmission pulses; Figures 3a and 3;
b is a signal waveform diagram to explain the filter blind point, Fig. 4 is a signal waveform diagram to explain the drawbacks due to switching between two transmission pulses, and Fig. 5 is a conventional pulsed Doppler radar device with two transmission pulses. A block configuration diagram showing an example, FIGS. 6a to 6d are signal waveform diagrams for explaining the operation of the gate converter shown in FIG. 5, and FIG. 7 is a diagram for explaining the drawbacks of the pulsed Doppler radar device shown in FIG. 8 is a block configuration diagram showing an embodiment of the pulsed Doppler radar device according to the invention, and FIGS. 9a to 9e are signal waveform diagrams for explaining the operation of the pulsed Doppler radar device of FIG. 8. It is. 32...PRF generator, 33, 34, 38, 4
2...PRF switcher, 37...gate converter, 3
9...Switching distance setter, 40...PRF selector,
41...PRF selection determiner.

Claims (1)

[Scope of utility model registration request] A transmitter that generates at least three types of repetitive signals having different repetition periods and switches and transmits a transmission pulse corresponding to each of the at least three types of repetitive signals, and a reflected signal of the transmission pulse transmitted by the transmitter. At least two combinations are set, each consisting of a receiver that detects a reflected signal from a moving target and two types of repetitive signals having different repetition periods from the at least three types of repetitive signals. a selector for selecting and deriving one combination having a large time difference between adjacent transmission pulses on the time axis from among the at least two combinations for each preset distance segment including distance information; Therefore, repetitive signals of the selected combination are supplied, and a determination signal is supplied to the transmitter to select the repetitive signal of the combination with a larger time difference from the target reflected signal and to transmit a transmission pulse corresponding to this repetitive signal. A pulse Doppler radar device comprising a determination circuit for determining