JPH0410993B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Technology to which the Invention Pertains) The present invention is directed to irradiating radio waves to targets such as aircraft, flying objects, or vehicles, and using the radio waves reflected from those targets as a medium to transmit radio waves to targets such as aircraft, flying objects, or vehicles. In a pulse-type distance tracking radar that tracks distances of
This invention relates to improvement of a distance tracking radar that automatically tracks the distance from the distance tracking radar to a target.

(Background of the present invention) Conventional distance measuring radars can be roughly divided into pulse type and continuous wave type, but in continuous wave type, the radio waves irradiated by the radar itself to the target always leak to the receiver inside the radar. Because of this, it was difficult to make the receiver highly sensitive. For this reason, pulse type distance measuring radars are relatively often used.

Due to the pulse modulation format used in pulse type radars, the receiver bandwidth must be wide in order not to sacrifice pulse width (distance resolution), as shown in the detector output 10 in Figure 6. Sensitivity is not very good due to increased receiver noise. Furthermore, because the receiver bandwidth is wide, it is vulnerable to radio wave jamming by the target side, which is a serious drawback.

Various methods have been proposed for radar technology to counter radio interference, but the frequency and format of the radio waves emitted by the radar itself towards the target are such that the target side cannot detect the radio waves. If it can be irradiated, it will be one of the fundamental solutions to counter radio interference.

For the reasons mentioned above, one direction in which distance measurement radars should go in the future is: (a) In the continuous wave system, the sensitivity of the receiver deteriorates due to the transmission output leaking into the receiver, so By using the pulse modulation format to switch between transmission and reception, and by making the pulse repetition frequency variable, it prevents the transmission pulse from matching the reception reflected wave pulse and prevents a drop in reception power. (a) Radio waves to be transmitted (c) By making the bandwidth as narrow as possible in the front stage of the receiver, cross-modulation interference is reduced and the anti-jamming ability is improved. There is a strong desire to simultaneously achieve these goals, such as improving sensitivity and increasing sensitivity.

(Prior Art and Its General Problems) A conventional example of a distance tracking radar will be described using the block diagram of FIG. 5 and the time chart of FIG. 6.

The reference pulse generator output 29, which is the output of the reference pulse generator 57, is waveform-shaped into a pulse having a predetermined pulse width by the shaping circuit 58, and becomes the reference pulse 23.

The source output 15 produced by the transmit source 59 is pulse modulated by a pulse modulator 60 to which the reference pulse 23 is applied, resulting in a pulse modulator output 24.
is amplified by the power amplifier 61 to become the power amplifier output 47, which is transmitted to the target as the transmission output 18 by the transmission antenna 50.

The reflected wave from the target is delayed by T (seconds) after transmission, and is received by the receiving antenna 51 as receiving input 1, and becomes receiving antenna output 2. Local oscillator output 13 produced by local oscillator 56 is supplied to mixer 52
is mixed with receiving antenna output 2 by
The signal is amplified by the intermediate frequency amplifier output 37, and is amplitude detected by the amplitude detector 54 to become the amplitude detector output 10. The display 55 displays the amplitude detector output 1 based on the reference pulse 23.
By displaying the distance calculation output 26 obtained from 0, the distance from the radar to the target can be determined.

(Specific problems with the prior art) Tracking radars that search for, detect, and track targets do not only have the ability to accurately track targets, but also lack the ability to accurately track targets even when they receive interference from the target side. is important.

Now, the transmission output 18 of the distance tracking radar in Fig. 5 is
When S ₁₈ , a signal of S ₁₈ =P(sinωpt)cosωt (1) is irradiated to the target. However, P
(sinωpt) is the pulse amplitude modulation signal of the transmission output 18 in FIG. 6, and ωp is the angular frequency of pulse repetition.

In this case, the target uses a frequency counter or a frequency analyzer to detect that a signal with an angular frequency ω is being emitted from the radar, and detects a signal with an angular frequency ω or noise with a center angular frequency ω. The modulated signal can be easily sent back,
It is possible to easily interfere with target tracking by the other party's radar.

The received input 1, which is a reflected wave from the target, that is, the received signal S ₁ is S ₁ =q[sinωp(tT)]cos[ω(tT)] (2). However, T is the round trip time from the radar to the target, and q[sinωp(t-T)] is the pulse modulation term of the received signal (therefore, the function q[sinωp(t
−T)] contains the function q[sinωp(t−T)]. ).

Knowing the time T, the distance to the target can be determined from the relationship 1 microsecond = 150 m. However, in order to determine the distance from the radar to the target, as shown in FIG.
It is necessary to obtain the amplitude detector output 10, which is a wideband signal as shown in the figure, and the receiver naturally becomes wideband, making it susceptible to interference. Therefore, one of the fundamental solutions from the viewpoint of radio wave interference of the distance tracking radar is to prevent the target side from knowing the transmission signal of the distance tracking radar.

(Objective of the present invention) The present invention modulates the transmission radio waves of the tracking radar into a two-phase modulation of 0 and π (pi) so that the frequency used by the radar is not easily detected on the target side. , an extremely radio-secure system that emits a wideband pulse wave phase-modulated with two phases of 0 and π (pi) toward a target, and can receive a wideband signal from the target at a narrow intermediate frequency. It is an object of the present invention to provide a two-phase modulation distance tracking pulse radar with high strength and anti-electromagnetic interference capability.

(Main points of the configuration of the present invention) Before explaining the embodiment shown in FIG. 1 in detail,
The principle of the present invention will be explained using the time charts shown in FIGS. 2 and 3.

In FIG. 2, the transmission output 18 is synchronized with the signal for pulse modulation (pulse shaping circuit output) 22.
is cosωt and −
Transmit cosωt signals alternately. Therefore, the receiver receives reception input 1, which is a reflected wave from the target, with a delay of time T (seconds) corresponding to the distance between the radar and the target. Since the reception input 1 is received as a pair of [cosω(t-T), -cosω(t-T)] like the transmission output 18 (the reception antenna output 2 is also the same), the bandwidth of the intermediate frequency amplifier is In a simple narrowband receiver that narrows and receives [cosω(t-T)
and −cosω(t−T)] is filtered by a narrow band filter, and the output becomes almost zero.

This means that from the standpoint of jamming radio waves, it is difficult to decipher the frequency and generate jamming waves, and radio waves are highly confidential.

Up to now, a case has been described in which cosωt and −cosωt are switched for each transmission, but this does not necessarily have to be the case, and it is sufficient if the number of occurrences of the 0 phase and the π phase is approximately the same.

Now, the transmission source output 15 (S ₁₅ ) is determined as follows.

S ₁₅ = sinωt (3) where ω is the angular frequency of the carrier wave of the transmission source output 15.

The third phase modulator output 16 (S ₁₆ ) is S ₁₆ =sin[ωt+π/2 Sign(sinωst)] (4). However, ωs is the angular frequency of the signal generator output 20. Furthermore, Signx=1 x>0 0 x=0 −1 x<0 (5).

The pulse modulator output 24, the power amplifier output 47 and the transmission output 18 (S ₁₈ ) can be expressed in the same way,
It will look like this:

S ₁₈ =P(sinωpt)sin[ωt+π/2 Sign(sinωst)]=P(sinωpt)sin[π/2Sign(sinωst)]cosωt...(6). However, S ₂₂ =P(sinωpt)...(7). This equation (7) indicates the pulse shaping circuit output 22.

In the case of the transmission output 18 in equation (6), the principle of demodulating the distance information of the reception input 1, which is a reflected wave from the target, will be explained. Reception input 1 (S ₁ ) is received with a delay of T than transmission, so S ₁ = q[sinωp(t-T)]×sin{π/2Sign [sinωs(tT)]}cosω(t-T)... …(8) becomes.

In order to drop the received input 1 (S ₁ ) to an intermediate frequency, a first mixer is used using two mutually orthogonal first phase modulator outputs (S ₇ ) and a second phase modulator output 8 (S ₈ ). 62 and a switching signal to the second mixer 63. Here, the first phase modulator output 7
(S ₇ ) is set as S ₇ =sin {π/2Sign[sinωs(t−τ)]}×cos[ω _l (t−τ)] (9). However, τ is the amount of delay, and ω _l is the oscillation angular frequency of the local oscillator 56. The second phase modulator output 8 (S ₈ ) is S ₈ =sin {π/2Sign[cosωs(t-τ)]}×cos[ω _l (t-τ)] (10). In addition, the following relational expressions, equations (11) and (12) sin{π/2Sign[sinωs(tT)]} ×sin{π/2Sign[sinωs(t-τ)]} ≒cosωs(T-τ)... ...(11) −sin {π/2Sign[sinωs(tT)]} ×sinπ/2Sign[cosωs(t-τ)]} ≒sinωs(T-τ) ...(12) holds true. However, is the average over one period.

Therefore, the first mixer output 3 (S ₃ ) is S ₃ =q[sinωp(tT)]cosωs(T−τ)×cos[t(ω− _ωl− (ωT− _ωlτ )]… ...(13) and becomes the reference signal of the synchronous detector 67.The second
Mixer output 4 (S ₄ ) is S ₄ =q[sinωp(tT)]sinωs(T−τ)×cos[t(ω− _ωl )−(ωT− _ωlτ )]……(14) Become.

The amplitude limiter output 25 (S ₂₅ ) is |cosωs(T-τ)|>0 ...(15) If the pulse modulation signal q[sinωp(t-T)]
The spectrum other than around the center frequency of both sideband waves is removed by the narrow band first intermediate frequency amplifier 64, and the signal of equation (13) is expressed as S ₂₅ =cos[t(ω−ω _l )−(ωT −ω _l τ)]……(16
), which becomes a reference signal to the synchronous detector 67.

Similarly, from the second intermediate frequency amplifier output 6 (S ₆ ), the spectrum other than the vicinity of the center frequency of both sideband waves is removed by the narrow band second intermediate frequency amplifier 65, and S ₆ = sinωs (T - τ). cos [t(ω-ω _l ) − (ωT-ω _l τ)] ...(17) This is a narrowband signal, but in equation (17), it is equivalent to the distance to the target, which is the purpose of the present invention. The round trip time T to the target is included in the amplitude component sinωs(T−τ) due to phase modulation, even though it is a narrowband signal.

In addition, the amplitude component sinωs (T−τ) due to phase modulation
is a synchronization error component, so it is a narrowband signal when T≈τ. The synchronous detector output 9 (S ₉ ) is S ₉ = ₂₅・₆ = sinωs (T - τ) (18), and since equation (18) can take positive and negative values around 0, the synchronous detector 67 is desirable as the output.

Therefore, if the distance radar can freely generate a signal corresponding to the distance T from the radar to the target, then T=τ... (19) By always setting equation (18) to 0, ,
Radar can track the target, and
The distance to the target can be determined from the known quantity τ.

Now that we know that the configuration described so far can measure distance, we can use the distance information (signal) to connect the transmission output 18 and reception input 1 (reflected waves from the target) when searching and tracking a target. We will discuss how to prevent overlap.

In FIG. 3, the transmission pulse width of the transmission output 18, that is, the pulse shaping circuit output 22 of FIG.
The pulse width of is γ, and the time from the trailing edge of the transmitting pulse signal to the leading edge of the receiving pulse signal of receiving input 1 (i.e. receiving antenna output 2) is α.
shall be. Considering a small target, the reception pulse width is approximately the transmission pulse width, so the reception pulse width is γ, and the time from the trailing edge of the reception pulse signal to the leading edge of the next transmission pulse signal is β. Here, α and β
means the minimum required time.

Now, let us consider pulse modulation with a small change in duty (ratio of pulse width to period) so as to reduce the change in average received power. An attempt is made to receive the received pulse signal in its complete form (pulse width γ). First, if the received pulse signal is immediately after the transmitted pulse signal as shown in Figure 3B (n=0,
However, n is the number of transmission pulses that occur between transmission and reception. In B of Fig. 3, when the receiving position of the target is between the transmission output 18 and the next transmission output 18, and the target is at the closest distance, the round trip time to the target is γ + α, similarly, the target reception position is between the transmission output 18 and the next transmission output 18. When the receiving position is between transmission output 18 and the next transmission output 18 and the target is at the farthest distance, the round trip time to the target is (2γ + β + α)
If the pulse period of the transmission output _{18 is} determined so that T + γ + β (21), and the period t ₀ changes between (2γ + α + β)≦t ₀ <2 (2γ + α + β) (22) from equations (20) and (21).

When n = 1, that is, when another transmission pulse enters between transmission and reception, the period t 1 is in the interval of (2γ + α + β) + γ + α ≦ T < 2 (2γ + α + _β ) + γ + α ... (23) t ₁ =T+γ+β/2 (24), and the period t ₁ changes by (2γ+α+β)≦t ₁ <3/2 (2γ+α+β) (25).

As shown in Figure 3C, when there are n transmitted pulses between the transmitted pulse signal and the received pulse signal (section P), n(2γ+α+β)+γ+α≦T<(n+1) (2γ+α+β)+γ+α...( 26) By setting the period tn as tn=T+γ+β/n+1 (27) in the interval, overlapping of the transmitted pulse and the received pulse can be prevented. Furthermore, the period tn changes by (2γ+α+β)≦tn<(n+2)/(n+1) (2γ+α+β) (28). Therefore, as can be seen from equation (28), when the target distance is far, the pulse repetition frequency changes little, so the average transmission power changes little.

Regarding target capture, change T in equation (27) from a small value to a large value (from short distance to long distance) or from a large value to a small value (from long distance to short distance), and change the distance and repetition frequency. If both are changed at the same time, it is possible to prevent the transmission output 18 and the reception input 1 from overlapping even though the duty is large, thereby improving the transmission efficiency of the transmission output 18.

(Embodiment of the present invention) An embodiment of the present invention shown in FIG. 1 will be described.

First, a state in which the distance tracking radar of the present invention is tracking a target at a distance will be explained.

Signal generator output 2 which is the output of signal generator 75
0 is the transmission source 59 in the third phase modulator 71
Phase modulates the transmission source output 15, which is the output of
The third phase modulator output 16 is obtained by performing phase modulation of two phases with a phase difference of π radians.

The distance signal generator output 46, which is a signal generated by the distance signal generator 76 and corresponds to the time T from when the radar irradiates a radio wave to a target until it is reflected back to the radar receiver, is generated by a pulse reference signal generator. 72, the pulse reference signal generator 72 calculates equations (26) and (27), and calculates whether the arrival time of the reflected wave from the target does not overlap with the transmission time of the transmission output 18. , becomes the pulse reference signal generator output 21, is made into a signal with a predetermined pulse width by the pulse shaping circuit 73, and becomes the pulse shaping circuit output 22.
becomes.

The third phase modulator output 16 becomes the pulse modulator output 24 by using the pulse shaping circuit output 22 as a modulating signal in the pulse modulator 60, and is amplified by the power amplifier 61 to output the power amplifier. 47, and the transmission power 18 is directed toward the target by the transmission antenna 50.

Reception input 1, which is a reflected wave from the target, is received by reception antenna 51 and becomes reception antenna output 2, which is then sent to first mixer 62 and second mixer 63.
, and using the first phase modulator output 7 and the second phase modulator output 8, respectively, the first
The frequency is converted into a mixer output 3 and a second mixer output 4, and the frequency is converted into a first intermediate frequency amplifier 64 and a second intermediate frequency amplifier 64, respectively.
The intermediate frequency amplifier 65 amplifies the first intermediate frequency amplifier output 5 and the second intermediate frequency amplifier output 6.
become. Further, the amplitude of the first intermediate frequency amplifier output 5 is made constant by an amplitude limiter 66 to become an amplitude limiter output 25, which becomes a reference signal to a synchronous detector 67. The second intermediate frequency amplifier output 6 is synchronously detected in a synchronous detector 67 to become a synchronous detector output 9, which is input to a distance signal generator 76 via a switch 85.

The other output of the signal generator output 20 is processed in a delay device 74 by using the distance signal generator output 46 as a control signal and changing the delay amount (corresponding to τ) so as to decrease the synchronous detector output 9. The output becomes the delay device output 19, and then the π/2 phase shifter 69 outputs π/2.
This results in a π/2 phase shifter output 27 whose phase is shifted by 2 radians. The local oscillator output 13 generated by the local oscillator 56 is the π/2 phase shifter output 2.
7, the first phase modulator output 7 is phase modulated and applied to the first mixer 62. On the other hand, the second phase modulator 8
2, the local oscillator output 13 is phase modulated by the delayer output 19 to create a second phase modulator output 8. This second phase modulator output 8 is fed to the second mixer 6
Added to 3.

Next, a method for searching for a target distance will be described. When the target is not detected, the second amplitude detector output 40, which is the output of the second amplitude detector 84 that amplitude-detects the first intermediate frequency amplifier output 5, is zero, so the switch 85 is activated by this output. is in a conductive state to the sweep oscillator 86 side. Since the sweep oscillator output 42 is a quantity proportional to T in equation (27), a distance search is performed from a short distance to a long distance according to the sweep oscillator output 42, and if a target is found, the second amplitude detector output 40 is used. When the signal is output, the switch 85 is switched to the synchronous detector 67 side, and the switch output 41 is input to the distance signal generator 76 to enter a tracking state.

(Supplementary Explanation of Embodiments) (A) Although the transmitting antenna and the receiving antenna are configured separately in FIG. 1, the same antenna may be used for transmitting and receiving.

(a) In FIG. 1, the case where the output of the signal generator 75 is a single spectrum such as a sine wave has been explained, but it may be a signal having a wide spectrum such as random noise.

(C) So far, we have explained an example in which phase modulation is performed every pulse repetition as shown in FIG. 2, but the transmission output 18 corresponding to the transmission source output 15 and the signal generator output 20 in FIG. Phase modulation may be performed within the pulse as shown in . Note that FIG. 4 shows a case where a random signal is binarized and phase modulated. This can be considered to be due to a change in the angular frequency ωs in equation (18).

(d) In order to create a signal delayed by the delay time τ, the first
In the figure, a variable voltage delay device 74 is used for explanation, but a plurality of time-series code generators that generate code signals of the same series using clock pulses are used to generate code signals used for transmission and code signals used for reception. Since the amount of delay of the code signal to be generated is proportional to the number of clock pulses, it is possible to use a digital code signal generator that changes the time at which the code signal occurs by changing the number of clocks on the delay side. good.

(Effects of the present invention) (1) Since the phase is transmitted in two phases, 0 and π radians, from the standpoint of causing radio wave interference, the second aspect of the present invention is
Since it is difficult to detect the phase signal, decipher the frequency, and send the interfering radio waves back to the other radar, it is a distance tracking radar with high radio secrecy and excellent resistance to radio interference.

(2) Even if single-frequency interference is applied to the distance tracking radar of the present invention, the spectrum will be dispersed outside the bandpass amplifier (intermediate frequency amplifier) placed after the mixer, so it will affect the receiver. There is little interference.

(3) Although it has not been possible to achieve accurate distance measurement with conventional narrowband reception radars, the present invention makes it possible to perform distance measurement with narrowband reception, and the disadvantage of matching the transmitted and received pulses is the inconvenience. This is made possible by synchronizing and changing the pulse interval and the delay time from transmission to reception, thereby improving the efficiency of transmission output.

(4) Since the frequency bandwidth of the bandpass amplifier can be narrowed, the unavoidable inherent noise in the receiver can be reduced, resulting in an extremely sensitive distance tracking radar.

(5) The distance measuring radar of the present invention can be used in the same radio wave format when used in combination with a narrowband reception type monopulse angle tracking radar, so this device can be used in combination with a monopulse tracking radar rather than being used alone. It can also be used as

(6) Pulse radar receivers use transmitter/receiver switching circuits and gate circuits to prevent leakage of the transmitting output 18, and gate circuits to prevent the receiver from becoming saturated by the transmitting signal, but especially when high When phase modulation is performed by frequency, direct leakage of the transmitted signal to the receiver due to the frequency difference between the transmitted signal and the local oscillator output is extremely reduced.

(7) Although it is a high-repetition radar with a large ratio of transmission pulse width to repetition period, the pulse repetition period is variable in synchronization with the target distance signal, and it can search over the entire distance without blind distance. This allows it to have the good properties of a narrowband continuous wave signal receiver, but with range resolution comparable to the range gated target searching capabilities of a non-coherent pulse radar. .

(8) In conventional pulse modulation radar, when the received signal, which is a reflected wave from the target, passes through a narrow-band intermediate frequency amplifier, it loses the component containing distance information (round trip time T to the target), but the phase When the modulated signal and the configuration according to the present invention are combined, a component containing distance information is output even though a narrow band intermediate frequency amplifier is used.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the distance tracking pulse radar according to the present invention, FIGS. 2 to 4 are time charts for explaining the embodiment, and FIG.
The figure is a block diagram showing a conventional distance tracking pulse radar, and FIG. 6 is a time chart for explaining the conventional example of FIG. 1...Reception input, 2...Reception antenna output, 3
...First mixer output, 4...Second mixer output, 5
...First intermediate frequency amplifier output, 6... Second intermediate frequency amplifier output, 7... First phase modulator output, 8...
...Second phase modulator output, 9...Synchronized detector output,
10... Amplitude detector output, 13... Local oscillator output, 15... Transmission source output, 16... Third phase modulator output, 18... Transmission output, 19... Delay device output, 20... Signal generation 21...Pulse reference signal generator output, 22...Pulse shaping circuit output, 23...Reference pulse, 24...Pulse modulator output, 25...Amplitude limiter output, 26...Distance calculator output , 27...π/2 phase shifter output, 28...
Voltage controlled oscillator output, 29... Reference pulse generator output, 36... Mixer output, 37... Intermediate frequency amplifier output, 40... Second amplitude detector output, 41...
...Switch output, 42...Sweep oscillator output, 46
... Distance signal generator output, 47 ... Power amplifier output, 50 ... Transmission antenna, 51 ... Reception antenna, 52 ... Mixer, 53 ... Intermediate frequency amplifier,
54...Amplitude detector, 55...Display device, 56...
Local oscillator, 57...Reference pulse generator, 58...
... Shaping circuit, 59 ... Transmission source, 60 ... Pulse modulator, 61 ... Power amplifier, 62 ... First mixer, 63 ... Second mixer, 64 ... First intermediate frequency amplifier, 65 ... ...Second intermediate frequency amplifier, 66...
Amplitude limiter, 67...Synchronous detector, 69...π/
2 phase shifter, 70...first phase modulator, 71...third phase modulator, 72...pulse reference signal generator,
73...Pulse shaping circuit, 74...Delay device, 75
... Signal generator, 76 ... Distance signal generator, 82
... second phase modulator, 84 ... second amplitude detector,
85...Switch, 86...Sweep oscillator.

Claims (1)

[Claims] 1. Transmission source, modulation means, transmitting antenna, receiving antenna, first and second mixers, local oscillator, first
and a second intermediate frequency amplifier, a synchronous detector, a delay device, a signal generator, and a distance signal generator, the distance tracking pulse radar comprising an output signal of the signal generator and an output signal of the distance signal generator. A transmitting signal obtained by pulse-phase modulating the output of the transmitting source by the modulating means is irradiated toward the target by the transmitting antenna, and a received signal having received a reflected wave from the target by the receiving antenna is transmitted to the target by the transmitting antenna. In addition to the first and second mixers, the outputs of the signal generator are delayed by a time corresponding to the propagation time from transmission to the target to reception using the delay device, and are made mutually orthogonal signals. Signals obtained by phase modulating the outputs of the local oscillators using the converted signals are respectively applied as switching signals to the first and second mixers, and the first and second mixers convert the received signals into two signals. the first and second intermediate frequencies for the necessary signals.
The output of one intermediate frequency amplifier is used as a reference signal, and the output of the other intermediate frequency amplifier is synchronously detected by the synchronous detector. detecting the position, returning the output signal of the synchronous detector to the distance signal generator, returning the output signal of the distance signal generator to the delay device to control the delay time, and synchronizing with the received signal; , the delay time T from transmission to reception of the reflected wave is determined by the following formula n(2γ+α+β)+γ+α≦T<(n+1) (2γ+α+β)+γ+α (where γ: transmission pulse width, α: from trailing edge of transmitted pulse to leading edge of received pulse β: the minimum time required from the trailing edge of a received pulse to the leading edge of the next transmitted pulse, n: the number of transmitted pulses that occur between transmission and reception) The pulse repetition period tn of the transmission signal is set to tn=T+γ+β/n+1, and the pulse repetition period tn and the output of the distance signal generator that controls the delay amount of the delay device are simultaneously changed to transmit the transmission signal. A distance tracking pulse radar that tracks a target by reducing the overlap between a signal and a signal received from the target. 2 Transmission source, modulation means, transmission antenna, reception antenna, first and second mixers, local oscillator, first
and a second intermediate frequency amplifier, a synchronous detector, an amplitude detector, a sweep oscillator, a delay device, a switch, a signal generator, and a distance signal generator, the distance tracking pulse radar comprising: an output of the signal generator; A transmission signal obtained by pulse-phase modulating the output of the transmission source by the modulation means using the output signal of the signal and distance signal generator is irradiated toward the target by the transmission antenna, and is reflected from the target by the reception antenna. The received signals received by the wave are applied to the first and second mixers, and the outputs of the signal generators are delayed by a time corresponding to the propagation time from transmission to the target to reception using the delay device, so that they are mutually delayed. orthogonalized signals, and signals obtained by phase modulating the output of the local oscillator using the orthogonalized signals are applied as switching signals to the first and second mixers, and the first and second mixing The received signals are respectively reduced to two intermediate frequencies by the receiver, and the necessary signals are amplified by the first and second intermediate frequency amplifiers, and the output of one intermediate frequency amplifier is used as a reference signal and the other intermediate frequency is amplified by the first and second intermediate frequency amplifiers. The output of the frequency amplifier is synchronously detected by the synchronous detector, and when the target is initially captured, the output of the sweep oscillator is inputted to the distance signal generator via the switch to change the pulse repetition period. When a target is searched and a signal indicating the presence of the target is detected by amplitude detection by the amplitude detector, the switch is switched from the sweep oscillator side to the synchronous detector side, and the synchronous detector performs synchronous detection. The output signal of the synchronous detector is returned to the distance signal generator via the switch, and the output signal of the distance signal generator is used to control the delay time. is returned to the delay device to synchronize with the received signal, and the delay time T from the transmission to the reception of the reflected wave is calculated by the following formula n(2γ+α+β)+γ+α≦T<(n+1) (2γ+α+β)+γ+α (however, γ : Transmission pulse width, α: Minimum required time from the trailing edge of the transmitted pulse to the leading edge of the received pulse, β: Minimum required time from the trailing edge of the received pulse to the leading edge of the next transmitted pulse, n: Transmission The pulse repetition period tn of the transmission signal is set to tn=T+γ+β/n+1 in the interval represented by The distance tracking pulse radar is characterized in that the target is tracked by simultaneously changing the output of the distance signal generator to reduce the overlap between the transmitted signal and the received signal from the target.