JPH0312264B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides information on radar, sonar, etc. in a round shape.
Regarding PPI display devices that display images on a CRT screen by sweeping an electron beam using the polar coordinate deflection method (PPI method),
In particular, the present invention relates to a PPI display device in which signal processing for PPI display is performed digitally. (Prior art) Conventionally, in this type of PPI display device, the generation of sine and cosine signals corresponding to the antenna angle, and also sine and cosine signals corresponding to the set angle of the azimuth line, was generated using an analog transmitter such as a resolver. However, the accuracy of the sine and cosine signals is determined by the mechanical and electrical accuracy of the transmitter, and increasing the accuracy increases the cost of the transmitter and has a limit to its accuracy. It has been difficult to increase the resolution of targets captured by radar, sonar, etc. beyond a certain level. Also, since all signal processing is analog, it is easily affected by temperature, so it is natural that electrical compensation is applied, but when used in relatively harsh environments such as ships, temperature compensation is required. Even if this method was carried out, the influence of temperature could not be completely eliminated, resulting in a problem of lack of stability. Therefore, in Japanese Patent Application No. 58-113491, the inventors of the present application digitally generated the antenna angle and the set azimuth angle, and further digitally generated the sine and cosine signals corresponding to the antenna angle and azimuth line angle signals. We have proposed a PPI display device that uses advanced signal processing. (Problem to be Solved by the Invention) By the way, this type of PPI display device used on ships, etc. is sometimes used in conjunction with a collision prevention device, and it is not possible to use a PPI display device that employs the above-mentioned digital signal processing.
There is no problem with the PPI display device when used as a standalone radar, but there are the following problems when it is linked with a collision prevention device. FIG. 3 is a schematic explanatory diagram when a digital PPI display device is linked to a collision prevention device, and the antenna angle transmitter 10 using a synchro transmitter, shaft encoder, etc. transmits an analog antenna angle signal proportional to the antenna angle. generates a signal, digital PPI display device 100 and collision prevention device 200
is giving to In the digital PPI device 100,
After converting the antenna angle signal from the antenna angle transmitter 10 into a digital signal, the corresponding digital data of sine and cosine are generated and each is converted into analog data. SH and smoothing circuits 24a and 24c are provided in the sine and cosine signal systems of the antenna angle in order to switch display with the cosine signal, and the sine and cosine signals corresponding to the antenna rotation angle are provided.
The cosine signal is sampled and held at a predetermined timing, smoothed, and then supplied to the radar sweep signal generator. The input signals to the smoothing circuit sections of the SH and smoothing circuits 24a and 24c are signals obtained by instantaneously sampling and holding the sine and cosine values corresponding to the antenna angle obtained at each transmission period via an analog switch. As shown in FIG. 4, the signal changes stepwise, and this stepwise changing signal is converted into a smoothly changing output signal by a smoothing circuit section and extracted. In smoothing processing by such a smoothing circuit section, a signal delay occurs between the input signal and the output signal due to smoothing, and a delay time τd occurs depending on the time constant of the smoothing circuit section. As shown in Fig. 5, this delay time τd is an angular delay θd of about 2 degrees in terms of angle on the actual radar display screen.
This will result in If such a delay angle θd occurs, when using the radar as a single unit, for example, if the antenna angle transmitter 10 is a synchro transmitter, adjusting the stator holding angle of the synchro transmitter to compensate for the delay angle θd will completely eliminate the problem. No problem. However, as shown in FIG. 3, when interlocking with the collision prevention device 200, the stator holding angle of the synchro oscillator is changed to correct the delay angle, and the collision prevention device 200 is operated in conjunction with the digital PPI display device 100. Since the synchro oscillator does not have such a delay element, it is necessary to perform correction to restore the correction made by the synchro oscillator, which becomes extremely complicated. On the other hand, if the delay angle θd is not corrected, an angular delay θd will occur between the actual radar sweep line and the original radar sweep line indicated by the broken line, as shown in FIG. Target tracking gate 202 and radar image 102 generated by the device 200
There was a problem of discrepancies between the two. (Means for Solving the Problems) The present invention has been made in view of the above-mentioned problems, and it solves the time delay caused by the smoothing process after sampling and holding the digitally generated sine and cosine signals of the antenna angle. The purpose of the present invention is to provide a PPI display device that corrects the delay time without affecting the interlocking collision prevention device.Since the delay time due to smoothing processing is known in advance, antenna correction corresponding to this delay time is provided. A digital angle setting device for digitally setting the angle is provided, and a digital adder adds the digital setting angle for correction by the digital angle setting device to the digital conversion signal of the antenna angle to generate sine and cosine digital data. It was designed to do so. (Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention. First, the configuration will be described. Reference numeral 10 denotes an antenna angle transmitter, and for example, a synchro transmitter or a shaft encoder (angle encoder) is used. 11
is a digital converter that converts the angle signal θ1 digitally output according to the antenna angle from the antenna angle transmitter 10 into a binary digital angle signal. As the digital converter 11, a synchro-digital converter is used when the antenna angle transmitter 10 is a synchro transmitter, and a pulse counter is used when the antenna angle transmitter 10 is an incremental type shaft encoder. Ru. Here, the binary digital angle signal converted by the digital converter 11 has the correspondence relationship between the binary angle bits and weight angles shown in Table 1 below, assuming that the number of bits is 12 bits, for example. .

[Table] As is clear from Table 1, the most significant bit MSBa1 of the digital angle signal represents 180, the weight of the second bit a2 below is reduced to half to 90, and the last 12th bit, the least significant bit LSBa12 teeth
It corresponds to 0.087890625. The antenna angle θ1 converted into a digital angle signal consisting of the binary bits shown in Table 1 above is
is supplied to one side of the digital adder 12, which is constructed using a required number (three in this example) of TI's 74LS83A, 74LS283, etc., for example. Further, the other input of the digital adder 12 is supplied with the antenna correction angle signal Δθ, which similarly consists of 12 binary bits in this example. What is this antenna correction angle correction signal Δθ? For example, if you want to display the radar display with the north direction directly above the PPI, which is called "NORTH UP," it is the deviation angle between the own ship's heading and the north direction. This is usually obtained directly from a gyro compass. In addition, if you want to display the screen with the set course of the ship called "COURSE UP" directly above the PPI, it is the angle of deviation between the own ship's heading and the set course, and the standard This can be obtained by measuring the ship's heading from the north using a gyroscope and the set course heading from the north, and finding the difference between them. Of course, when displaying the screen with the normal heading called "HEAD UP" directly above the PPI, there is no need for correction, so set the correction angle to Δθ = 0.
You can leave it as . If only "HEAD UP" is displayed, the digital adder 12 may be omitted and the output of the digital converter 11 may be directly supplied to the digital adder 32. In this way, in the digital adder 12,
The sum of the two input angles (θ1+Δθ) is determined, and this signal is applied to one input of the digital signal switch 17. In order to simplify the explanation, in the following explanation, the "HEAD UP" display will be taken as an example, and the antenna correction angle Δθ will be treated as zero. The output of the digital angle setter 30 is supplied to the other input of the digital adder 32, and this digital angle setter 30 is configured to adjust the signal delay time in the S/H and smoothing circuits 24a and 24b, which will be explained later. It has a function to set the feed angle θd of the sweep line on the CTR screen converted according to τd. To explain in more detail, the digital angle setter 30 can set any angle using a digital value of multiple bits, and if we assume that the angle can be set using 6 bits, the lower 6 bits a7 to a of Table 1 above
It has a correspondence relationship between the binary angle bits and weight angles shown in Table 2 below, which corresponds to 12.

[Table] According to the 6-bit data in Table 2, it is possible to set the delay angle θd corresponding to any delay time τd from 0 degrees to approximately 5.6 degrees. The delay angle θd set by the digital angle setter 30 in this way is given to the digital adder 32, and is added to the antenna angle θ1 obtained via the digital adder 12 as a corrected antenna angle (θ1+θd). The signal is supplied to one input of a digital signal switch 17 provided at the next stage. The output θ2 from the electronic azimuth angle digital transmitter 13 is applied to the other input of the digital signal switch 17. Here, the electronic azimuth angle digital transmitter 13 is
The setting azimuth of the azimuth line to be displayed on the CRT screen is generated digitally, and can be configured by, for example, a binary addition/subtraction counter. By subtraction, a digital azimuth representing the desired azimuth θ2 is generated as the count value of the addition/subtraction counter. The digital data of the azimuth angle θ2 generated by the electronic azimuth angle digital transmitter 13 is also the 12-bit digital data shown in Table 1 above, similar to the binary digital data of the digital converter 11 that outputs the digital angle signal of the antenna angle. It becomes binary digital data. The output of the electronic azimuth angle digital transmitter 13 is
At the same time, the electronic azimuth angle digital transmitter 1 is supplied to the other input of the digital signal switch 17.
The signal is also supplied to a binary/BCD converter 14 provided for numerically displaying the azimuth angle θ2 set to 3. The binary/BCD converter 14 is, for example, a PROM.
It uses digital data representing the set azimuth angle θ2 from the electronic azimuth angle digital transmitter 13 as the address signal of the PROM, and uses a BCD that is pre-stored in an address corresponding to the digital data representing the azimuth angle. The code is configured to be read from the address data θ2 from the electronic azimuth angle digital transmitter 13. Binary/
The BCD code representing the set azimuth angle θ2 read out from the BCD converter 14 is the data latch circuit 1.
5, the setting azimuth angle θ2 is latched at fixed time intervals, and the set azimuth angle θ2 is displayed numerically on the LED numerical display 16 by driving display segments using LEDs, such as angles in units of 0.1, such as "000.0" to "359.9". It is configured to do so. In this way, the electronic azimuth angle digital transmitter 1
Since the set azimuth angle θ2 of the azimuth line is numerically displayed on the LED numerical display 16 in real time based on the binary data from step 3, the operator can set the desired azimuth angle θ2 while looking at the display on the LED numerical display 16. settings can be made. On the other hand, the digital data representing the antenna angle (θ1 + θd) supplied to the digital signal switch 17 and the digital data representing the azimuth angle θ2 of the azimuth line are operated by the digital signal switch 17 based on a switching control signal supplied from the outside. Either one of the input data is read out and supplied to the sine generator 18 and the pre-sine generator 19. The sine generator 18 and the cosine generator 19 are, for example, binary/BCD
Like the converter 14, it can be configured with a PROM, and the digital data of the antenna angle (θ1 + θd) or the digital data of the azimuth angle θ2 supplied from the digital signal switch 17 is used as address data, and the PROM is configured in advance to correspond to the address data. The stored sine and cosine values are read out by addressing with each digital data, and sine digital data and cosine digital data are output, respectively. Data latch circuits 20a, 20b, 20c, and 20d latch sine and cosine value data (including sign and numerical data) from the sine generator 18 and cosine generator 19, respectively. That is, the sine digital data read out from the sine generator 18 is sent to the data latch circuit 20a,
Otherwise, it is latched to 20d and that value is held. Similarly, the cosine digital data read out from the cosine generator 19 is latched by the data latch circuit 20c or 20b, and its numerical value is held. The outputs of the data latch circuits 20a, 20b, 20c and 20d are respectively applied to a digital signal selector 21.
selects one of these four latch inputs, outputs it, and supplies it to the D/A converter 22 at the next stage. In this embodiment, the D/A converter 22 converts 12-bit digital data into an analog DC voltage having positive and negative polarities such as ±1V or ±5V. The output of the D/A converter 22 is supplied to each of analog switch circuits 23a, 23b, 23c and 23d. Analog switch circuit 23a~
23d is in a conductive (ON) state or non-conductive (OFF) by a control signal supplied from the outside.
It is an element that can take two states; when it is in a conductive state, it outputs the input positive and negative DC voltages as is, while when it is not conductive, the input voltage is not output. In this way, the respective output voltage signals from the analog switch circuits 23a to 23d are transmitted to the corresponding S/H and smoothing circuits 24a and 23d.
4b, 24c and 24d. Here, the S/H circuit is an abbreviation for sample-and-hold circuit, which samples and takes in the input voltage value supplied when the analog switch in the previous stage is conductive.
The analog switch holds its value during non-conduction time. In this embodiment, as will be explained later, the input signal is sampled during 1/4 of one cycle, and the remaining 3/4 is held. Also, the smoothing circuit uses the previous input value E _o-1
and the current input value E _o , the voltage difference ΔE = E _o −E _o-1
This is a circuit that smooths out the sharp changes in signal voltage that occur on the output side when there is no smoothing circuit, and extracts it as an output signal with a temporally smooth change.As shown in Figure 4, this signal smoothing allows A delay time τd occurs between the input step signal and the smoothed output signal, which depends on the smoothing time constant. However, in the present invention, a corrected antenna angle (θ1 + θd) is created in advance in the digital adder 32 by a delay angle θd on the CRT screen corresponding to the delay time τd of the smoothing circuit, and the sine and cosine data are Since this occurs, the sine and cosine components of the antenna angle θd, which are corrected due to the delay in the smoothing circuit, are removed, and the smoothing circuit outputs an analog signal based on the sine and cosine values corresponding to the correct antenna angle θ1. be done. The outputs of the S/H and smoothing circuits 24a and 24b are each supplied to an analog switch 25a, and similarly the outputs of the S/H and smoothing circuits 24c and 24d are each supplied to an analog switch 25b. The analog switching devices 25a and 25b each select one of the two input signals and output it to the output side. The outputs from the analog switches 25a and 25b are respectively sent to the sweep signal generator 26.
a and 26b, a sawtooth-varying sweep signal is generated by integrating signal voltages proportional to sine and cosine, which have already been converted from digital data to analog data and smoothed. After current amplification with
A deflection current is supplied to each of the orthogonal deflection coils 28a and 28b of the CRT, and information based on the antenna angle θ1 or an azimuth line based on the set azimuth angle θ2 is displayed by sweeping the deflection of the electron beam on the CRT screen. Further, the sweep signal generators 26a and 26b are simultaneously supplied with an off-center control signal in the X-axis direction (horizontal direction) and an off-center control signal in the Y-axis direction (vertical direction) from the outside, and are supplied with the sweep signal for the antenna angle and the azimuth. The starting points of the line sweep signals can be independently moved to arbitrary positions. Next, the operation of the present invention in FIG. 1 will be explained with reference to the signal waveform diagram in FIG. First, an analog antenna angle signal from an antenna angle transmitter 10, for example a synchro oscillator, is constantly converted into a 12-bit binary angle signal θ1 in a digital converter 11, for example a synchro digital converter. has been added to the input. In addition, the digital adder 12
Since the antenna correction angle signal Δθ, which also consists of 12 binary bits, is supplied to the other input of
The sum of these two signals (.theta.1+.DELTA..theta.) is always outputted to the output side of the digital adder 12. Here, to simplify the explanation, taking as an example the antenna correction angle signal Δθ=0, the digital adder 12 outputs the antenna angle signal θ1 from the digital converter 11 as it is. The output of the digital adder 12 is input to one of the digital adders 32, and the sum of the set angle θd from the digital angle setter 30 for the other input is outputted (θ1+θd). That is, the digital angle setter 30 is connected to the S/H and smoothing circuit 24.
By setting the delay time τd generated in a and 24c, the 6-bit corrected angle data given in Table 2 is output, and the digital adder 32 adds it to the antenna angle signal θ1 and adds it to the corrected antenna angle signal θ1. The antenna angle signal (θ1
+θd). On the other hand, in response to the setting operation by the operator to set the azimuth line in an arbitrary direction, the electronic azimuth angle digital generator 1
The count value of the addition/subtraction counter changes according to the addition operation signal or subtraction operation signal for 3, and the azimuth angle θ set in this electronic azimuth angle digital transmitter 13 changes.
The binary digital data of No. 2 is given as address data to the binary/BCD converter 14, and the BCD code corresponding to the address data is read out and latched into the data latch circuit 15 at fixed time intervals.
A numerical value is displayed on the LED numerical display 16, and an arbitrary azimuth angle can be set by looking at the numerical display on the LED numerical display 16. In this way, the electronic azimuth angle digital transmitter 13
The set azimuth angle θ2 of the azimuth line set at Either the signal (θ1+θd) or the digital azimuth signal θ2 from the electronic azimuth angle digital transmitter 13 is selected and outputted from the digital signal switch 17. Now, in devices such as radar or sonar,
A periodic trigger signal e1 as shown in FIG. 2 is generated, and radio waves and ultrasonic waves are periodically transmitted based on this. This trigger signal e1 is the timing control circuit 29
, the timing control circuit 29 sequentially generates the following timing signals. First, the antenna angle selection signal e as shown in FIG.
2 and supplies it to the digital signal switch 17. The digital signal switch 17 immediately receives the input signal (θ1+θd) from the digital adder 32.
Select and output this. Next, the timing control circuit 29 generates a latch signal e3 of the antenna angle sine/cosine as shown in FIG.
supply to c. Then, the antenna angle signal (θ1 + θd) from the digital signal switch 17 is supplied to the sine generator 18 and cosine generator 19 as address signals, respectively, and as a result, the sine generator 18 and cosine generator 19 output address data (i.e. The sine and cosine values corresponding to the angle data) are read out, and these values are applied to the data latch circuits 20a and 20c.
are latched to each of them. Next, the timing control circuit 29 generates an electronic azimuth angle selection signal e4 as shown in FIG. Since the digital signal switch 17 immediately selects and outputs the input signal θ2 from the electronic azimuth angle digital transmitter 13, this signal θ2 is similarly given to the sine generator 18 and the cosine generator 19 as address data, and the sine A sine value and a cosine value corresponding to the electronic azimuth angle θ2 are read from the generator 18 and the cosine generator 19. Next, the timing control circuit 29 generates an electronic azimuth sine/cosine latch signal e5 as shown in FIG.
This is supplied to data latch circuits 20b and 20d. Therefore, data latch circuits 20b and 20d
latches the sine and cosine values corresponding to the electronic azimuth θ2, respectively. The data latch circuit 2 is activated by the two latch signals e3 and e5 from the timing control circuit 29.
Latched 2 of 0a, 20c and 20b, 20d
The set latch output signals vary as shown in FIGS. 6 and 7. That is, it shows that two sets of data are each latched after a certain period of time from the trigger signal e1. Subsequently, the timing control circuit 29 generates the antenna angle sine selection signal e6 shown in FIG. 2 and supplies it to the digital signal selector 21 and the analog switch circuit 23a. As a result, digital data indicating the sine value of the antenna angle (θ1 + θd) from the data latch circuit 20a is selected by the digital signal selector 21, which is converted into an analog voltage by the D/A converter 22, and is further brought into a conductive state. S/ through the analog switch circuit 23a
The signal is sampled and held by the H and smoothing circuit 24a. Next, the timing control circuit 29 generates the antenna cosine selection signal e7 as shown in FIG.
Finally, through the same operation as the antenna sine selection signal e6, the S/H and smoothing circuit 2
At 4c, an analog voltage representing the cosine value of the antenna angle (θ1+θd) is sampled and held. Next, the timing control circuit 29 generates an electronic azimuth angle sine selection signal e8 as shown in FIG. An analog voltage representing the sine value of the electronic azimuth θ2 is sampled and held. Next, the timing control circuit 29 generates an electronic azimuth angle cosine selection signal e9 as shown in FIG. An analog voltage representing the cosine value of the electronic azimuth θ2 is sampled and held. In this way, the sine and cosine values of the antenna angle (θ1 + θd) and the electronic azimuth angle θ2 are adjusted to the S/H and smoothing circuit 24a, respectively, within one trigger period.
24c, 24b, and 24d, and this operation is periodically repeated every time a trigger signal is generated, and the changes in each cycle are smoothed out. here,
In signal smoothing by the smoothing circuit, a signal delay τd occurs at the input and output, so the antenna angle (θ1 +
S/ which handles sine and cosine signals of θd)
The correction amount θd added by the digital adder 32 is removed due to the signal delay in the H and smoothing circuits 24a and 24c, and the correct antenna angle θ1 is
Analog sine and cosine values corresponding to the above are always output from the S/H and smoothing circuits 24a and 24c, respectively. Of course, the electronic azimuth θ2
Analog sine and cosine values corresponding to the above are also constantly output from the S/H and smoothing circuits 24b and 24d. Note that since the electronic azimuth angle θ2 is fixedly set, it is only a DC component, and since the repetition period of the electronic azimuth angle sweep signal is sufficiently larger than the period of the antenna angle sweep signal, it is not affected by delays due to signal smoothing. Next, the timing control circuit 29 is shown in FIG.
An antenna angle sweep selection signal e10 or an electronic azimuth angle sweep selection signal 10 such as No. 3 is generated and supplied to analog switches 25a and 25b. When the antenna angle sweep selection signal e10 is supplied to the analog switches 25a and 25b,
The sine and cosine values corresponding to the antenna angle θ1 from the S/H and smoothing circuits 24a and 24c are selected and sent to the sweep signal generators 26a and 26b.
and analog switching devices 25a and 25
When the electronic azimuth angle sweep selection signal 10 is supplied to the electronic azimuth angle sweep selection signal 10, the sweep generators 26a and 2 from the S/H and smoothing circuits 24b and 24d, respectively.
6b. Therefore, the sweep signal generators 26a and 26b generate sweep signals that vary in a sawtooth pattern by integrating the sine and cosine voltage signals, and provide the sweep signals to the sweep current amplifiers 27a and 27b. At this time, if X-axis and Y-axis off-center control signals are externally supplied to the sweep signal generators 26a and 26b, the sweep starting point can be moved from the origin, which is the center of the CRT screen, to any position on the CRT. Can be done. The sweep current amplifiers 27a and 27b can perform a sweep operation on the CRT by current amplifying the input sweep signal and passing it through the orthogonal deflection coils 28a and 28b. In addition, by stopping the antenna angle sweep signal once every N times (for example, 32 times) and replacing it with the electronic azimuth angle signal, the PPI
The sweep of the electronic azimuth line can be displayed simultaneously with the sweep of the antenna angle on the screen. Of course, it is normally possible to display video signals, distance mark signals, etc. on the PPI at the same time in synchronization with the antenna angle sweep signal. (Effects of the Invention) As explained above, according to the present invention, even if a signal delay occurs due to smoothing of sampled and held sine and cosine signals, the signal delay can be dealt with in advance when generating digital sine and cosine data. Since the sine and cosine data are generated by correcting the antenna angle by the angle, the correction amount is removed by the signal delay in the smoothing circuit, and analog signal voltages with sine and cosine values corresponding to the correct antenna angle are always output. This eliminates the need for adjustment to remove signal delay on the antenna angle transmitter side when used as a standalone radar, and also eliminates the need for adjustment to remove signal delay on the antenna angle transmitter side. This has the effect of preventing PPI display of the radar sweep line and reliably preventing mismatch between the tracking gate by the collision prevention device and the radar target on the screen. Of course, since the sine and cosine values corresponding to the antenna angle and electronic azimuth angle are generated by digital signal processing, by increasing the number of data bits to 12 bits, extremely high calculation precision can be achieved and high precision can be achieved. Radar image and direction line
PPI display is possible, and commercially available ICs can be used as circuit elements for digital signal processing, making them highly reliable and inexpensive.Furthermore, since digital signal processing is used, temperature and electrical The influence of noise is significantly reduced, and it is possible to demonstrate sufficiently stable performance even in harsh environments such as ships.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a time chart showing the operating signal waveform of the embodiment of Fig. 1, and Fig. 3 is the interlocking relationship between the PPI display device and the collision prevention device. Schematic explanatory diagram showing 4th
The figure is a signal waveform diagram showing the signal delay caused by the S/H and smoothing circuit built into the PPI display device. Figure 5 shows the radar image when the signal delay occurs and the tracking gate set to prevent collision. It is an explanatory view showing a shift. 10: Antenna sensitivity oscillator, 11: Digital converter, 12, 32: Digital adder, 13:
Electronic azimuth angle digital generator, 14: binary/
BCD converter, 15, 20a to 20d: data latch circuit, 16: LED numerical display, 17: digital signal switch, 18: sine generator, 19: cosine generator, 21: digital signal selector, 22:
D/A converter, 23a to 23d: Analog switch, 24a to 24d: S/H and smoothing circuit, 25
a, 25b: analog switch, 26a, 26b:
Sweep signal generator, 27a, 27b: sweep current amplifier, 28a, 28b: orthogonal deflection coil, 29: timing control circuit, 30: digital angle setter, 100: PPI display device, 200: collision prevention device.

Claims (1)

[Claims] 1. An antenna angle signal transmitter that generates an antenna angle signal; A digital angle converter that converts the antenna angle signal from the antenna angle transmitter into a digital angle signal; For any azimuth setting operation a digital azimuth generator that digitally generates a set azimuth of an azimuth line to be displayed on a round CRT screen according to the timing; a sine/cosine generator that generates digital data of sine and cosine corresponding to the digital angle signal or digital azimuth signal selected by the digital signal switch; a data holder that holds sine data and cosine data corresponding to each of the digital angle and digital azimuth output from the generator; and a signal selection that sequentially selects the output of the data holder according to a set timing. a digital-to-analog converter that converts the output of the signal selector into an analog signal; sample-holding the output signal of the digital-to-analog converter through an analog switch that is sequentially selected according to a set timing; A smoothing circuit that smoothes the output signal of the sample and hold circuit; An analog signal switch that selects the output signal of the smoothing circuit according to a set timing; An output signal of the analog signal switch a sweep signal generator that generates an antenna angle sweep signal or an azimuth line sweep signal proportional to; and a current amplifier that supplies a deflection current to the orthogonal deflection coil of the CRT by current amplification proportional to the output signal of the sweep signal generator. The PPI display device is equipped with a digital angle setting device for setting a display delay angle on a CRT screen corresponding to a signal delay time caused by signal smoothing in the smoothing circuit, and the digital angle setting device is added to the digital angle by a digital adder provided between the digital angle converter and the digital signal switch to correct the display delay angle of the sweep line.