JPH0211876B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial Application Field The present invention relates to a PPI radar device used in ships, aircraft, etc., and particularly relates to a PPI radar device that displays target images by switching distance ranges. (b) Prior art Conventionally, in the display of received video signals in radar equipment using the polar coordinate sweep method (hereinafter referred to as "PPI"), a sweep signal is started at the same time as the transmission pulse is sent out by the radar antenna, and the display is performed over a period of time according to the radio wave propagation distance. The received video signal received over the course of time is fed to the CRT display in real time to display the target object image. Therefore, when changing the display distance range for a CRT screen, the sweep time and
and the sweep repetition frequency is changed. However, when the sweep time changes due to changing the distance range, the display brightness of the CRT screen changes, and the display screen becomes dark, especially in the short range where the sweep time is short. On the other hand, the number of distance ranges that can be switched is usually about 9 to 10, and a circuit that generates a sweep waveform at a different time is required for each range, which increases the complexity of the circuit and increases the cost.
In addition, short sweeps in short distance ranges increase the power density for CRT deflection drive, shortening the life of the CRT display.Furthermore, short sweep waveforms have poor linearity, and it is expensive to maintain linearity. The problem was that it required a circuit. (c) Purpose of the Invention The present invention has been made in view of these conventional problems, and it is an object of the present invention to provide a PPI radar device that can maintain uniform brightness of the display screen even if the distance range is changed. With the goal. Another object of the present invention is to obtain a high-brightness image that allows a large number of people to view radar images at the same time even if the distance range is changed without blocking external light to the display screen with a hood or the like. Another object of the present invention is to keep the sweep time constant even when the distance range changes, and to simplify the circuit configuration and reduce costs by eliminating the need to provide a sweep signal generation circuit with a different sweep time for each distance range. There is a particular thing. Another object of the present invention is to improve display quality by increasing the number of scanning lines when a long distance range is set. (d) Structure and operation of the invention In order to achieve these objects, the PPI radar device of the present invention first keeps the sweep display period Ts constant even if the distance range changes, and on the other hand, the transmission and reception period Tt
For short range, Tt=Ts/N, for medium range, Tt=Ts, and for long range, Tt=
MTs (however, N and M are integers such as 1, 2, 3, etc.). In other words, in terms of frequency, for example, the sweep frequency s is always constant at s = 2KHz, whereas the transmission/reception frequency t is t = Ns = 4K over a short range.
Hz (N=2), t=s=2KHz for medium range, and t=s/M=0.5KHz (M=4) for long range. Next, the received video signal obtained periodically is A/D
Basically, the converted digital video signal is written to the storage device using real-time processing, and the written digital video signal is read out using timing control that matches the sweep period. Different controls are performed for each range. In other words, for short ranges, the sweep display period
Since the video signal reception period Tt is shorter than Ts,
Determine Ts/Tt=N, select 2N storage devices, sequentially write the received digital video signal video for 2N periods, and write to N storage devices in the previous sweep period in parallel with this writing. The digital video is read out in parallel, and its average value or peak value is output and displayed in a sweep manner. Next, in the medium range, since Ts=Tt, two storage devices are selected, digital video is alternately written and read, and a sweep display is performed based on the read digital video. For even longer range settings, the sweep display cycle
Since the video reception cycle Tt is longer than Ts, digital video writing is the same as in the middle range, but for reading, Tt/Ts=M is determined and the same digital video is recorded for one reception cycle Tt. The readout display is repeated M times. (e) Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. First, to explain the configuration, 10 is a radar antenna rotated at a constant speed by a motor 12, and a transmitter 14 supplies transmission pulses at a predetermined repetition period to the radar antenna 10. Pulse radio waves are repeatedly transmitted in the directional direction of the radar antenna 10 based on the supply of the radar antenna 10. The transmitter 14 uses a frequency t=1KHz in the short range based on the distance range selection by the range setting device 44, which will be explained later.
A transmission pulse signal with a period corresponding to the transmission frequency is output, with t=2KHz in the middle range and t=0.5KHz in the long range. A receiver 16 receives and amplifies reflected radio waves received over time corresponding to the distance due to the reflection of pulse radio waves from the radar antenna 10, and outputs the amplified radio waves as a received video signal. 18 is A/
The D converter converts the video signal received from the receiver 16 into, for example, a 4-bit digital signal. Each of 20, 22 and 24 is a selector and selects a storage device into which the digital video signal from the A/D converter 18 is written. 26, 28, 3
0 and 32 are storage devices in which digital video signals are written and read, respectively;
Specifically, a shift register, RAM (random access memory), or the like is used. Here, if the number of video data used for one sweep display is, for example, 480, then the storage device 26
-32 each has a storage area consisting of 480 4-bit configurations. 34 and 36 are arithmetic units, and the arithmetic units 34 and 36 calculate the average value of two periods of digital video signals read out in parallel from the storage devices 26, 28 or 30, 32 when the short distance range is selected. It has a function of detecting the maximum value, and in the middle range and long range, it functions as a gate that simply passes the read digital video signal. 38 is a selector that selects the readout output from the storage devices 26 to 32 outputted via the arithmetic unit 34 or 36, and 40 is a D that converts the digital video signal read out via the selector 38 into an analog signal. /A
The converter 42 is a CRT display that displays the received video signal converted into analog by the D/A converter 40 on a CRT screen by PPI sweeping. Here, the sweep display period Ts and sweep frequency on the CRT display 42
s is set to a constant value regardless of the distance range, and specifically, s is set to 2KHz. 44 is a distance range setting device, which in this embodiment has nine switching ranges, including a short range
S ₁ ~ S ₃ , medium range M ₁ ~ _{M 3} and long range
Equipped with L ₁ to L ₃ as switching ranges. 46 is a timing controller, and distance range setting device 44
Selector 20, 2 based on the range setting signal from
2, 24, and 38, and timing signals for writing and reading data into and from storage devices 26, 28, 30, and 32, respectively. 48 is a selection control circuit, which selects the selectors 20, 22, 24 based on the timing signal from the timing controller 46.
and 38 selection controls. Reference numeral 50 denotes a write/read clock selector, which controls writing/reading and supplies write/read clocks to the storage devices 26, 28, 30, and 32 using a timing signal based on the distance range from the timing controller 46. Let's do it. Here, the propagation time of radar radio waves for the distance range in the distance range setter 44, the transmission/reception repetition frequency, and the sweep time and sweep frequency in the sweep display are determined, for example, as shown in Table 1 below.

[Table] As is clear from this table-1, distance range 1/
The short range is 4, 3/4, 1.5 knots,
Distance ranges 3, 6 and 12 knots are medium ranges, and distance ranges 24, 48 and 120 knots are long ranges, and the propagation time of radar waves in each range increases as the distance increases. . Also, the transmitting and receiving frequency t is determined as 4KHz for the short range, 2KHz for the medium range, and 0.5KHz for the long range, while the sweep time is the same for each range, 148.34μs, and the sweep frequency is also the same for each range. = 2KHz. Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained. First, in the distance range setting device 40, the range S ₁
In the short range setting where any of the steps _.about.S3 is selected, control is performed based on the time chart shown in FIG. 2. That is, when one of the short range ranges S ₁ to _{S 3} is selected, as is clear from Table 1 above, the transmission frequency of the transmission pulse by the transmitter 14 changes.
t=4KHz, the sweep frequency of the CRT display 42
Since s is constant at 2KHz, the reception cycle Tt of the received video obtained by the receiver 16 is the same as that of the CRT display 4.
This is half the time of the sweep display period Ts in 2.
For this short range selection, the timing controller 46 selects 2N=4 storage devices 26, 28, 30 and 32 are selected as storage devices for short range use. In this state, for example, if a pulse radio wave is transmitted from the radar antenna 10 with a transmission pulse from the transmitter 14 based on the first transmission trigger as shown in FIG. outputs a selection signal e ₁ to the selector 20 and connects the output of the A/D converter 18 to the selector 22 . At the same time, the selection control circuit 48 supplies the selection signal e ₂ to the selector 22, and the selector 22 selectively connects the storage device 26. Therefore, the received video signal received by the receiver 16 using the first transmitted pulse radio wave is digitally converted by the A/D converter 18 and then sent to the storage device 26 via the selectors 20 and 22.
is supplied as video data M1. At this time, the storage device 26 is supplied with a write clock from the write/read clock selector 50 in synchronization with the transmission trigger, and the digital data of the received video obtained at the reception cycle shown by cycle _T1 in FIG. Signal M1 is written to memory 26 in real time. Next, when a transmission trigger occurs second, the selector 22 selectively connects the storage device 26 according to the selection signal _e2 from the selection control circuit 48, and the digital video signal M2 from the A/D converter 18 is transferred to the selector 20, 22 to a storage device 28, and the storage device 28 receives the digital video signal M2 obtained at the receiving period shown as period T2 in FIG. ₂ based on the write clock from the write/read clock selector 50. storage device 2
8 in real time. Next, when the third transmission trigger occurs, the selection control circuit 48 selectively connects the selector 20 to the selector 24 side, and connects the output of the selector 24 to the storage device 30 by the selection signal _e3 . Therefore, the period in Figure 2
A/D converter 18 obtained with a reception period indicated by T ₃
The digital video signal M3 from the selector 20,
24 to the storage device 30, and writing is performed based on the read clock of the write/read clock selector 50. On the other hand, simultaneously with the write control to the storage device 30, the selection control circuit 48 selectively connects the selector 38 provided at the output stage of the storage device to the arithmetic unit 34 side by outputting the selection signal e4, and at the same time controls the write/read clock. A read clock is supplied from the selector 50 to the storage devices 26 and 28 in which the digital video signals M1 and M2 are written through periods T ₁ and T ₂ , and the periods written in the storage devices 26 and 28 are
The digital video signals M1 and M2 for T ₁ and T ₂ are read out in parallel and supplied to the arithmetic unit 34. In the arithmetic unit 34, the periods T ₁ and T ₂ read out in parallel
The average value of each of the digital video signals M1 and M2 is calculated, or one of the digital video signals having the maximum value is selected and sent to the D/V signal via the selector 38.
After being supplied to the A converter 40 and converted into an analog video signal by the D/A converter 40, the CRT display 42
The target signal obtained at periods T ₁ and T ₂ is displayed as an image using a sweep signal having a sweep frequency s=2KHz. As is clear from the time chart in FIG. 2, this read control from the storage devices 26 and 28 continues even while the received video is being written to the storage device 32 in period _T4 based on the fourth transmission trigger. The digital video signals M1, M2 written in the storage devices 26 _, 28 are then read out over a sweep display period Ts which is twice the write period T1, _T2 . Subsequently, when the writing of the digital video signal M4 to the storage device 32 for a period _T4 is completed and the next transmission trigger is generated, the storage device 26 is again
Writing control of digital video signals is performed. Simultaneously with this write control, reading from the storage devices 30 and 32 to which the digital video signals M3 and M4 have been written is performed in the same manner at periods T ₁ and T ₄ , and this process is repeated thereafter. Control processing in such a short range is
In contrast to writing of the received video in real time, the readout of the written received video is performed in a sweep display that is twice the reception period by parallel reading of two cycles of write data at a time that matches the sweep display cycle Ts. The display brightness of the CRT screen does not decrease when switching to the short range because the sweep display cycle does not change even if the reception cycle of the received video is shortened by selecting the short range. In addition, since the digital video signals read out in parallel are averaged, for example, even if one of the written data contains a noise component, the noise level will be reduced to 1/2 by averaging. , target display SN
It is possible to increase the ratio. On the other hand, when selecting the peak value, the one with the higher signal level is selected from among the digital videos read out in parallel, so even if the target has weak reflected radio waves, the target can be clearly displayed on the display screen. I can do it. Next, the range M ₁ is set in the distance range setter 44.
The operation when one of the medium-range ranges _.about.M3 is selected will be explained with reference to the time chart in FIG. 3. For selection of the intermediate range in the distance range setter 44, the timing control circuit 46 uses two of the four storage devices 26, 28, 30, 32;
For example, the storage devices 26 and 30 are selected as the storage devices used for medium-range writing and reading, and the other storage devices 28 and 32 are not used. Also, the above table-
1, the transmission frequency t of the transmitter 14 is switched to t=s=2 KHz, which is the same as the sweep frequency s in the CRT display 32. If the first transmission trigger is generated in this state as shown in FIG.
Based on this, the selection control circuit 48 selects the selectors 22 and 2.
4 is fixedly selectively connected to the storage devices 26 and 30, and the selector 2 is connected in synchronization with the first transmission trigger.
The selector 20 selectively connects the storage device 26 according to the selection signal e1 for 0. Therefore, A/D converter 1
The digital video signal M1 with a period _T10 outputted from 8 is sent to the storage device 26 via selectors 20 and 22.
is supplied to the memory device 26 based on the write clock from the write/read clock selector 50. Next, when a second transmission trigger occurs, the selector 20 is selectively connected to the storage device 30,
Digital video signal M from A/D converter 18
2 is written to the storage device 30. This storage device 3
Write to storage device 26 at the same time as writing to 0/
A read clock is supplied from the read clock selector 50, and in the middle range, the arithmetic unit 34 exists only as a gate circuit, and the selector 38
Since 1 is selectively connected to the arithmetic unit 34 side by the selection signal e4, 1 read from the storage device 26
The digital video signal M1 before the cycle is supplied to the D/A converter 40, and after analog conversion,
A sweep display is performed on the CRT display 42. If a third transmission trigger subsequently occurs, the storage device 26 writes the digital video signal again, and at the same time, the storage device 30 reads the digital video signal M2 written at _T11 one cycle before. , is converted into analog by an A/D converter 40, and then displayed in a sweep manner on a CRT display 42. In this manner, in the medium range setting, the received video signal is alternately written and read in the two selected storage devices. Next, the operation when the long distance range is selected will be explained with reference to the time chart in FIG. Assuming that one of the ranges L ₁ to _{L 3} is selected by the distance range setter 44, the transmission frequency t of the transmitter 14 is determined based on the setting of the long range, as is clear from Table 1 above. is switched to t=0.5KHz, which is 1/4 of the sweep frequency s. Also, when setting the timing controller 46 for the long range, the timing controller 46 uses the storage devices 26, 28, 30, and 32 in the same way as for the middle range.
two of the storage devices, e.g. storage device 26,
30 is selected as the storage device used for long-range storage control, and the other storage devices 28 and 32 are not used. In addition, in order to use the storage devices 26 and 30 for long-range storage control, the selectors 22 and 24 are selectively connected to the storage devices 26 and 30 in a fixed manner.
Further, the selector 38 is selectively connected to either the arithmetic unit 34 or 36 by the selection signal e4. In this state, if the first transmission trigger shown in the time chart of FIG. The received digital video signal M1 outputted from the A/D converter 18 based on the storage device 2
6 in real time based on the write clock from the write/read clock selector 50. Next, when the second transmission trigger occurs, the selector 20 is selectively connected to the storage device 30, and the A/D
Digital video signal M2 from converter 18 is written to storage device 30 in real time based on the write clock. Simultaneously with this writing in the storage device 30, a read clock is supplied from the write/read clock selector ₅₀ to the storage device 26 into which the digital video signal obtained in the previous period T30 is written, and the data is written in the period _T31 . The loaded digital video signal M1 is read out. Here, since the sweep display period Ts of the CRT display 42 is 1/4 of the writing period T ₃₁ to the storage device 30, read control of the storage device 26 is performed as shown in the time chart of FIG. During the period _T31 during which writing is being performed on the device 3, reading from the storage device 26 is repeated four times. In other words, at long range, Tt/Ts=s/t=2KHz/0.
Since an integer M such that 5KHz=4=M is given, reading from the storage device storing the digital video signal of one cycle before is repeated M=4 times. Furthermore, if a third transmission trigger occurs,
At the same time as writing control is performed again on the storage device 26, reading from the storage device 30 to which the digital video signal M2 was written in the previous period _T31 is performed. _M =
The reading is repeated four times. By repeating reading from the storage device M=4 times in such a long range, the received video signal for one cycle is written.
The same sweep display of the received video signal is repeated four times on the CRT display 42, and the fifth
As shown in the CRT screen 52 in the figure, in the readout display in the long distance range of the present invention, three sweep displays are added as shown in broken lines between the scanning lines 54 synchronized with writing shown in solid lines. By quadrupling the density of the scanning lines, the resolution of the displayed image is improved, greatly improving the display quality of targets displayed on the CRT screen. In the above embodiment, the sweep frequency s is set to a constant value of s=2KHz in each distance range, but the present invention is not limited to this, and any sweep frequency can be determined. Furthermore, although the integer N that determines the number of storage devices used in the short range 2N is set to 2 in the above embodiment, N can be any integer greater than or equal to 2. , and the case where the number of times of reading of the storage device in a long range is set to M=4 is taken as an example.
Similarly, any integer can be selected as M. Furthermore, although the above-mentioned embodiment takes a radar device as an example, the display control associated with range switching of the present invention can also be applied to a sonar or ultrasonic flaw detection device that displays and processes periodic received signals in the same way as a radar device. can be applied as is. (f) Effect of the invention PPI of the present invention clarified through the above explanation
The effects of the radar device are as follows. First of all, the sweep period (sweep frequency) of the CRT display is always constant when the distance range is changed, so even if the reception period is shortened by switching to the short distance range, the sweep display time does not change. , the brightness of the display screen can be maintained uniformly at both medium and long distances. Additionally, since a single sweep waveform can be used for multiple distance ranges, there is no need to generate sweep waveforms with different sweep times for each distance range, which simplifies the sweep signal generation circuit and significantly reduces costs. I can do it. Further, since the linearity of the sweep waveform does not deteriorate even in the short distance range, no deterioration in display quality is observed in the short distance range. Furthermore, since a common sweep signal can be used for multiple distance ranges, high brightness of the display screen can be achieved by configuring the system to generate a sweep signal that provides sufficient display brightness for the display screen. This allows a large number of people to view the display screen at the same time, which was difficult with conventional radar equipment. Furthermore, in a long distance range, the received video signal obtained in one reception period is swept and displayed multiple times, which improves the density of scanning lines on the CRT screen and improves the resolution and display quality of the display screen. I can do it.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a time chart showing short range control, Fig. 3 is a time chart showing medium range control, and Fig. 4 is a time chart showing control in a medium range. The figure is a time chart showing the control of the long distance range, and FIG. 5 is an explanatory diagram of the CRT screen showing the increase in the number of scanning lines in the long distance range. 10...Radar antenna, 12...Motor, 1
4...Transmitter, 16...Receiver, 18...A/D
Converter, 20, 22, 24, 38...Selector, 2
6, 28, 30, 32...Storage device, 34, 36
...Arithmetic unit, 40...D/A converter, 42...
CRT display, 48...Selection control circuit, 50...
Write/read clock selector, 46... timing controller, 44... distance range setter.

Claims (1)

[Claims] 1. A PPI radar device that displays a target image on a CRT screen by PPI sweeping of an electron beam, comprising an analog/digital conversion means for digitally converting a received video signal received by a radar antenna; a plurality of storage means for writing and reading digital video signals output from the digital conversion means; and at least a short range, a medium range, and a long range for setting the range of the target object image to be displayed on the CRT screen. A distance range setting means is provided with a switching range, and the distance range setting means switches the transmission/reception period Tt of the transmission pulse to Tt=Ts/N for a constant sweep display period Ts by setting the short distance range, and the middle distance range is set by the distance range setting means. The transmission control means switches Tt=Ts by setting Tt=Ts, and further switches Tt=MTs by setting long distance range, and the short range setting by the distance range setting means allows the transmission of signals received within one sweep display period Ts. 2N storage means, which is twice the number N of reception periods Tt of the received video signal, are selected, and 2N period worth of digital video signals are sequentially written into the selected 2N storage means, in parallel with the writing. The digital video signals for N cycles written in the N storage means are read out in parallel within the previous sweep display cycle Ts, and the average value or maximum value of the N digital video signals is output. A distance storage control means and a medium distance range setting by the distance range setting means select two of the plurality of storage means and store one cycle of received video signals received within one transmission/reception cycle Tt. medium-range range storage control means for writing the digital video signal into one of the storage means, and reading out the digital video signal written in the other storage means in the previous transmission/reception cycle in parallel with the writing; In setting the long distance range by the distance range setting means, two of the plurality of storage means are selected, and one cycle of the digital video signal of the received video signal received within one transmission/reception cycle Tt is stored in one of the storage means. a long-distance storage means for repeatedly reading the digital video signal written in the storage means M times and written in the other storage means in the previous transmission/reception cycle in parallel with the writing; and and display means for converting the digital video signal into analog and displaying it on a CRT screen, and the short-range range control means further comprises a display means for converting the digital video signal into analog and displaying it on a CRT screen; is set as the transmission frequency, select four storage means, write digital video signals for four periods obtained within two sweep display periods of 2Ts sequentially to the four storage means, and write the digital video signal in parallel with the writing. A PPI radar device characterized in that two cycles of digital video signals written in two storage means within the previous transmission display cycle Ts are read out in parallel.