JPH0448193B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention emits radio waves from a transmitting antenna to targets such as aircraft, flying objects, or vehicles, and transmits radio waves reflected from those targets to a medium. In a distance tracking radar that tracks the distance of a target, the emitted radio waves are transmitted in a highly secretive wideband modulation format, and the reflected waves from the target are received by a narrowband receiver to track the distance to the target. This paper relates to improvements in distance tracking radar.

[Conventional technology]

Conventional distance radars can be roughly divided into pulse type and continuous wave type. Continuous wave type radars are used because the radio waves emitted by the radar to the target always leak into the receiver inside the radar. It was difficult to make it highly sensitive. For this reason, pulse type distance measuring radars are relatively often used. Pulse radar requires a wide receiver bandwidth due to the pulse modulation format used.
Sensitivity is not very good due to increased receiver noise. Furthermore, because the receiver bandwidth is wide, it is vulnerable to band interference caused by the target side, which is a serious drawback. Various methods have been proposed for radar technology to counter radio interference, but the radar itself irradiates the target with electromagnetic waves in the form of radio waves that are undetectable to the target due to the frequency and format of the radio waves it emits towards the target. If it can be done, it will be one of the fundamental solutions to counter radio interference.

For the reasons stated above, one direction that monopulse radar should take in the future is: (a) If the sensitivity of the receiver deteriorates due to leakage of transmitted output into the receiver, use the pulse method. By switching between transmission and reception and further varying the pulse repetition frequency, the transmission pulse and the reception reflected wave pulse are prevented from matching, thereby preventing a drop in reception power.

(b) For the format of radio waves to be transmitted, use a frequency spectrum as wide as possible and select a modulation format that is highly confidential.

(c) By narrowing the bandwidth as much as possible in the front stage of the receiver, cross-modulation interference is reduced, anti-electromagnetic interference capability is improved, and sensitivity is increased.

(d) Realize demodulation of angle signals and distance signals in conventional monopulse angle measurement radar using a narrowband reception method.

There is a strong demand for their realization.

A conventional example of a distance tracking radar will be explained using the conventional example shown in FIG. 4 and the time chart shown in FIG. The reference pulse generator output 29, which is the output of the reference pulse generator 57, is waveform-shaped by a shaping circuit 58 to become a reference pulse 23 having a predetermined pulse width. Transmission source output 15 produced by transmission source 59 is pulse modulated by pulse modulator 60 to become pulse modulator output 24 and amplified by power amplifier 61 to become power amplifier output 47; By means of transmit antenna 60, transmit power 18 is transmitted towards a target. The reflected wave from the target is delayed by T (seconds) from the transmission, becomes reception input 1, is received by the reception antenna 51,
The receiving antenna output becomes 2. The local oscillator output 13 produced by the local oscillator 56 is mixed with the receiving antenna output 2 by the third mixer 52,
It becomes the third mixer output 36, is amplified by the third intermediate frequency amplifier 53, becomes the third intermediate frequency amplifier output 37, is amplitude detected by the amplitude detector 54, and becomes the amplitude detection output 10. . The distance from the radar to the target can be determined by displaying the amplitude detection output 10 on the display 55 using the reference pulse 23 as the reference pulse.

Note that the third intermediate frequency amplifier 53 is a wideband intermediate frequency amplifier because it is necessary to maintain the pulse width of the received reflected wave from the target.

[Problem that the invention seeks to solve]

In a tracking radar that searches for, detects, and tracks a target, it is important not only to accurately track the target, but also to have the ability to accurately track the target even in the face of interference from the target side. Now transmit signal 18
S ₁₈ , a signal of S ₁₈ =P(sin ω _p t)cos ωt (1) is irradiated to the target. However, P(sin ω _p
t) is the pulse amplitude modulated signal of FIG.
ω _p is the angular frequency of pulse repetition. The goal,
A frequency counter or frequency analyzer detects that a signal with an angular frequency ω is emitted from the radar, and sends a signal with an angular frequency ω or a noise modulation signal with a frequency whose center angular frequency is ω to the radar. can be easily sent back, easily interfering with target tracking by the other party's radar. The received signal S ₁ which is a reflected wave from the target is S ₁ =q[sin ω _p (t-T)] cos [ω(t-T)] (2). However, T is the round trip time from the radar to the target, and q[sin ω _p (t−T)] is the pulse modulation term of the received signal 1.

Therefore, the function q [sin ω _p (t-T)] is the function P
[sin ω _p (t-T)] is included. To find the distance from time T to the target, 1 microsecond ≒ 150m
It is found from the relationship. In order to find the distance from the radar to the target, a broadband signal q[sin ω _p (t
-T)], the receiver naturally has a wide band and is susceptible to interference. Therefore, one fundamental solution from the standpoint 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.

This invention modulates the modulation format of the transmitted radio waves of the distance tracking radar by targeting a wideband pulse wave that is position modulated with two phases of O and π (pi) so that the frequency used by the radar is not easily detected on the target side. It is an extremely radio-secrecy device that can emit light to the target and receive wideband signals from the target using a narrow band of intermediate frequencies.
The purpose of the present invention is to provide a two-phase modulation distance tracking radar with high anti-electromagnetic interference capability.

[Means for solving problems]

The distance tracking radar according to the present invention has 2 of O and π.
It emits a phase-modulated broadband pulse wave toward a target, demodulates the broadband signal from the target, and receives it at a narrow band of intermediate frequencies.

[Effect]

The operation and principle of this invention will be explained in the second section.
This is done using the time chart shown in Figure 3.

In FIG. 2, the transmission output 18 causes signals of cos ωt and -cos ωt to be transmitted alternately, where ω is the angular frequency of the carrier wave. Therefore, the received reflected wave has a time T corresponding to the distance between the radar and the target.
The input signal 1, which is a reflected wave from the target, is received with a delay of (seconds). Like the transmission output 18, the input signal 1 is received as a pair of [cos ω(t-T), -cos ω(t-T)], so it is received by narrowing the bandwidth of the intermediate frequency amplifier. In a narrowband receiver, [cos
The pair ω(t-T), -cos ω(t-T)] uses the principle that convolution on the time axis is multiplication on the frequency axis, so that signals with opposite phases to each other can be narrowbanded. filtering by a filter, i.e.
Since it is equivalent to integrating cos ω(t-T)
Only the difference between and -cos ω(t-T) remains, and if the appearance times of both are approximately the same, the output spectrum of the narrowband filter will be almost zero. Therefore, since single-frequency interference waves that have no correlation with the transmitted signal are not demodulated by the first mixer 62 and the second mixer 63, the output of the narrow band filter becomes almost zero, and the influence of interference is reduced. So far, we have explained the case where cos ωt and -cos ωt are switched for each transmission, but this does not necessarily have to be the case. For example, in the case of an M-series pseudo-random code, the appearance times of the O phase and the π phase are almost the same. Good to have. Therefore, the transmission source output is determined as _15S15 .

S ₁₅ =sin ωt (3) where ω is the angular frequency of the carrier wave of the transmission source output 15. If the time waveform of the phase modulation signal is sin ω _s , the third phase modulator output 16S ₁₆ becomes S ₁₆ = sin [ωt + π/2 sign (sin ω _s t)] (4), and the pulse modulator output 24 and the high frequency amplifier Since the output 47 and the transmission output 18S ₁₈ can be expressed in the same way, S ₁₈ = P (sin ω _p t) sin [ωt + π/2 sign (sin ω
_s t)] = P (sin ω _p t) sin [π/2 sign (sin ω _s t)
]cos ωt(5). where S ₂₂ =P(sin ω _p t) (6), where Equation (6) is the pulse shaping circuit output 22 and ω _s is the angular frequency of the signal generator output 20.
Furthermore, sign X=
1 X>0 0 X=0 (7) −1 X<0. The reception input 1S _1, which is the reflected wave from the target due to the transmission output 18 in equation (5), is received with a delay of T after the transmission, so S ₁ = q[sin ω _p (t-T)] sin{π/ 2sign〔sin
ω _s (t-T)〕}cos ω(t-T) (8) In order to reduce the receiving input 1S ₁ to an intermediate frequency, the first phase modulator output 7S ₇ and the second phase modulator output 8
_S8 is used as a switching signal to the first mixer 62 and second mixer 63. The output of the signal generator 75 after passing through the delay device 74 {sinπ/2sign [sin ω _s (t- π)]} and the output of the local oscillator 56 cosω [ _l (t-τ)]
If mixed in the first phase modulator 70, the first phase modulator output 7S ₇ becomes S ₇ =sin {π/2sign [sin ωt(t-τ)]}cos[
ω _l (t−τ)](9). Here, ω _l is the angular frequency of the output signal of the local oscillator 56, and τ is the time delay from transmission to reception. On the other hand, the phase of the signal from the signal generator 75 whose bits have been inverted by the inversion bit generator 66 is inverted at an angular frequency twice that of the output signal of the signal generator 75, so that sin {π/2gign[sin ω _s (t−τ) sin2ω _s (t−τ
)]}, and the output cos[ω _l (t−τ)] of the local oscillator 56 becomes
If mixed in the second phase modulator 82, the second phase modulator output 8S ₈ becomes S ₈ =sin {π/2sign [sin ω _s (t−τ) sin2ω _s (t
−τ)]}cos[ω _l (t−τ)](10). Next, in preparation for finding the mixer output of the received signal, the first phase modulator output (7), and the second phase modulator output 8, the phase modulation term sin {π/2 sign [sin ω _s (t−τ)]} and equations (9) and (10), the following relational expressions (11) and (12) hold.

sin{π/2Sign[sin ω _s (t-T)}sin{π/2s
ign[sin ω _s (t-τ)]}≒cos ω _s (T-τ)(11) −sin{π／2sign[sin ω _s (t-τ)]}sin{π
/2sign [sin ω _s (t−τ) sin2ω _s (t−τ)]} ≒1/2 sin 2ω _s (T−τ) (12) where is the time average of one period.
Therefore, the first mixer output _3S3 mixes the received signal of equation (8) with the first phase modulator output (7) _S7 of equation (9) and passes through the narrow band filter, so the time average S ₃ = q[sin ω _p (t-T)] cos ω _s (T-τ) cos
[t(ω- _ωl )-(ωT- _ωlτ )](13) This becomes the reference signal for the second synchronous detector 67.
The second mixer output 4S ₄ is a time-averaged value obtained by mixing the received signal of equation (8) and the second phase modulator output 8S ₈ of equation (10) and passing through a narrow band filter. S ₄ = q [sin ω _p (t-T)] 1/2 sin2ω _s (T-τ
)cos[t(ω− _ωl )−(ωT−ωτ)](14).

Since the first intermediate frequency amplifier output 64S ₆₄ is band-limited to suppress high frequency components due to modulation, both sideband waves q [sin ω _P (t-T)] are excluded.
The signal in equation (13) is S ₆₄ =cos[t(ω− _ωl )−(ωT− _ωlτ )]・cos
ω _s (T−τ)(16). Similarly, the second intermediate frequency amplifier output (6) S ₆ is
After removing both sideband waves, S ₆ = 1/2 sin2ω _s (T−τ)cos[t(ω−ω _l )−
(ωT−ω _l τ)](17). Second synchronous detector output regarding distance information (9)
S ₉ is, S ₉ = ₆₄・₆ = 2/1 sin2ω _S (T−τ)・cos ω _S
(T-τ)=cos ² ω _S (T-τ)・sin ω _S (T-τ)(1
8) Equation (18) shows that it is desirable as the output of the second synchronous detector 67 because it can take positive and negative values around O.

Therefore, if a distance tracking radar can freely generate a signal corresponding to the distance T from the radar to the target, then T = τ (19), and by always setting Equation (19) to O, the radar can track the target and determine the distance to the target.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The signal generator output 20, which is the output of the signal generator 75, is obtained by phase modulating the transmission source output 15, which is the output of the transmission source 59, in the third phase modulator 71, and generates a two-phase signal having a phase difference of π radian. The third phase modulator output 16 is phase modulated. Time T generated by the distance signal generator 76 until the radar irradiates radio waves to the target and the radio waves return to the radar.
The distance signal generator output 46 is a signal corresponding to
is calculated in the pulse reference signal generator 72 to determine whether the arrival time of the reflected wave from the target does not overlap with the transmission time of the transmission output 18, and becomes the pulse reference signal generator output 21. The signal is shaped into a pulse width signal and becomes the pulse shaping circuit output 22. The third phase modulator output 16 is
By using the pulse shaping circuit output 22 as a modulation signal in the pulse modulator 60, it becomes the pulse modulator output 24, which is amplified by the power amplifier 61 to become the power amplifier output 47, and by the transmitting antenna 50, The transmitted power 18 is directed towards the target. Reception input 1, which is a reflected wave from the target, is received by reception antenna 51, becomes reception antenna output 2, is branched to each of first mixer 62 and second mixer 63, and is output to first phase modulator output 7. and second phase modulator output 8 to become the first mixer output 3 and the second mixer output 4, respectively. The first mixer output 3 is amplified by the first intermediate frequency amplifier 64, and the first intermediate amplifier output 5 is amplified by the first intermediate frequency amplifier 64.
This becomes the reference signal for the second synchronous detector 67.
The second mixer output 4 is amplified in a second intermediate amplifier and becomes the second intermediate frequency amplifier output 6, which becomes the second intermediate frequency amplifier output 6.
The signal is synchronously detected in the synchronous detector 67 and becomes a distance error signal 9, which is input to the distance signal generator 76.

The other output of the signal generator output 20 delays the signal generator output 20 by τ in a delay device 74 so that the signal generator output 20 is always kept in synchronization with the receiving input 1.
That is, the delay amount of the delay device 74 is changed by the distance signal generator output 46 so that the distance error signal 9 is always zero, and the delay amount is changed to the delay device output 19, and the local oscillator output 13 generated by the local oscillator 56 is 1
In the phase modulator 70 , the signal is phase modulated and becomes the first phase modulator output 7 . On the other hand, the phase of the other delay output 19 is inverted by an inversion bit generator 66. This inverted signal and the non-inverted delay device output 19 are connected to the first switch 7.
7, the first switch output 27 is synthesized by switching each bit at the same angular frequency ω _s as the signal generator output 20 at an intermediate timing. This first switch output 27 phase modulates the local oscillator output 13 in a second phase modulator 82 to become a second phase modulator output 8 .

The above example explains that it is possible to irradiate a broadband pulse wave modulated with two phases of O and π toward a target, demodulate the broadband signal from the target, and receive it at a narrowband intermediate frequency. Ta.

In the above embodiment, the transmitting antenna and the receiving antenna are configured separately, but the transmitter may be configured with the same antenna. Moreover, although the case where the output of the signal generator has a single spectrum such as a sine wave has been described, it may be a signal having a wide spectrum such as random noise. Furthermore, as shown in Fig. 2, we have so far explained an example in which phase modulation is performed for each pulse repetition.
As shown in Figure 3, when the phase is modulated within the pulse, the zero part that occurs when the phase is modulated for each pulse repetition disappears, and the phase-modulated pulses are adjacent to each other, that is, the angular frequency ω of the pulse repetition The only difference is the relationship between _P and the angular frequency ω _s of the signal generator output, but the transmission output S ₁₈ in equation (5) is the same, and it can be applied in the same way. Note that FIG. 3 shows a case where a random signal is binarized and phase modulated. in this case,
The angular frequency ω _s in equation (18) can be considered as the fundamental angular frequency corresponding to one bit.

〔Effect of the invention〕

(1) Since the phase is transmitted in two phases of O 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 the distance tracking radar of the present invention is subjected to interference at the first frequency that has no correlation with the transmitted signal, it will not be demodulated by the mixer and will be spread to the opposite wide band.
There is less interference to the receiver because the spectrum is spread outside the band of the narrowband intermediate amplifier placed after the mixer.

(3) Conventional narrowband reception radars have not been able to achieve accurate distance measurement, but the present invention makes it possible to perform narrowband reception distance measurement, and the transmitted and received pulses match. This problem can be overcome by synchronizing and changing the pulse interval and the delay time from transmission to reception.
Transmission output efficiency improves.

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

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a distance tracking radar according to an embodiment of the present invention, and FIGS.
A time chart for explaining the embodiment shown in the figure, FIG. 4 is a block diagram showing a conventional distance tracking radar,
FIG. 5 is a time chart for explaining the conventional example shown in FIG. In the figure, 1 is the reception input, 2 is the reception antenna output, 3 is the first mixer output, 4 is the second mixer output, 5 is the first intermediate amplifier output, 6 is the second intermediate amplifier output, and 7 is the first Phase modulator output, 8 is second phase modulator output, 9 is distance error signal, 10 is amplitude detector output, 13 is local oscillator output, 15 is transmission source output, 16 is third phase modulator output, 18 is Transmission output, 19 is delay device output, 20 is signal generator output,
21 is the output of the pulse reference generator, 22 is the output of the pulse shaping circuit, 23 is the reference pulse, 24 is the output of the pulse modulator, 26 is the output of the distance calculator, 27 is the output of the first switch, 29 is the output of the reference pulse generator, 36 is the third mixer output, 37 is the third intermediate frequency amplifier output,
46 is a distance signal generator output, 47 is a power amplifier output, 50 is a transmitting antenna, 51 is a receiving antenna,
52 is a third mixer, 53 is a third intermediate frequency amplifier,
54 is an amplitude detector, 55 is a display, 56 is a local oscillator, 57 is a reference pulse generator, 58 is a shaping circuit, 59 is a transmission source, 60 is a pulse modulator, 61 is a power amplifier, 62 is a first mixer , 63 is a second mixer, 64 is a first intermediate frequency amplifier, 62 is a second intermediate frequency amplifier, 66 is an inverted bit generator, 67 is a second synchronous detector, 70 is a first phase modulator, 71 is a first 3 phase modulator, 72 is a pulse reference signal generator, 7
3 is a pulse shaping circuit, 74 is a delay device, 75 is a signal generator, 76 is a distance signal generator, 77 is a first switch, and 82 is a second phase modulator. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1 transmitting antenna, receiving antenna, first and second mixers, local oscillator, first and second intermediate frequency amplifiers,
In a distance tracking radar equipped with a synchronous detector or multiplier, a delay device, and a signal generator, a signal obtained by phase modulating the output of a transmission source using the output signal of the signal generator that generates a signal for phase modulation, The transmitting antenna irradiates the target, the receiving antenna receives the reflected wave from the target, the output of the receiving antenna is added to the first and second mixers, and the first mixer receives the output of the receiving antenna. of,
mixing the output of the local oscillator with the output of the first phase modulator modulated by a signal delayed by a time corresponding to the propagation time from transmission to the target to reception compared to the output signal of the signal generator; In the second mixer, the output of the receiving antenna is modulated by a second phase modulator which modulates the output of the local oscillator with a signal in which the first half of each bit of the delayed signal is in phase and the second half is in antiphase. It is mixed with the output and converted into two intermediate frequencies, amplified by the first and second intermediate frequency amplifiers whose bands are limited so as to suppress high frequency components due to modulation, and synchronized by the synchronous detection or multiplier. A distance tracking radar that detects the position of a target using a signal obtained by detection or multiplication.