JPS6255583A - Radar signal transmission system - Google Patents

Abstract

PURPOSE:To minimize the signal loss, by performing a received signal processing such as a suppression of clutter using a stagger trigger system and a pulse Doppler system. CONSTITUTION:A stagger trigger unit 70 comprises a trigger interval setter 71, a sequence determining circuit 72 and a trigger generation circuit 73. The setter 71 sets several different trigger intervals in such a manner that the difference from an average interval value is '0' in the mean. The circuit 72 determines the array sequence of trigger interval value so as to meet the requirement of minimizing the squared mean of the differences from these average interval values on the basis of several trigger interval values thus set. The circuit 73 generates a trigger signal to control the generation timing of a transmission pulse signal at an transmitter 20 according to the array sequence thus determined and the trigger interval value. This can minimize the signal loss.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radar signal transmission method suitable for use in a radar device that performs received signal processing using a Nords Doppler method.

[Technical background of the invention and its problems] FIG. 3 shows a schematic configuration of a general radar device.

In this radar device, a high frequency oscillator 10 is a circuit that generates a stabilized high frequency signal of a predetermined frequency, and the generated signals are supplied to a transmitter 20 and a receiver 50, respectively. The transmitter 20 generates a false signal having a required repetition period based on this input signal, and supplies it to the air 40 via the transmitter/receiver switch 30. The Norse signal is radiated from the antenna 40 as a transmission signal. On the other hand, the reflected wave from the target is
The signal is received by the airborne antenna 40 and supplied to the receiver 50 via the transmitter/receiver switch 30. This receiver 50
As described above, the oscillation signal of the high frequency oscillator 10 is also supplied to the oscillator, and the received signal is mixed with this oscillation signal and demodulated. The receiver 50 also has a built-in filter circuit for removing unnecessary signals such as clutter.
A signal from which unnecessary signals have been removed by this filter circuit is supplied to the display 60 and displayed.

Incidentally, as the above-mentioned filter circuit, an MTI (moving target indicator) is widely used. This is a band-removal filter that has a cutoff band set at the part where the K, so-called Doppler frequency, is "0" in order to mainly remove ground clutter caused by reflections from the ground surface.
Generally, it has output characteristics as shown in FIG. The PRF (Nockles repetition frequency) shown in FIG. 4 represents the reciprocal of the 14 pulse interval in the transmission pulse signal.

However, these prefectures! In a pulse radar using a filter, due to its characteristics, the above-mentioned arm repetition frequency PR
There is also a disadvantage that an attenuation range due to the MTI74 router occurs even at Doppler frequencies that are integral multiples of F. However, this can be avoided by adopting a transmission method called a staggered trigger method in which the nodal intervals of the radar signal to be transmitted are set at unequal intervals. In this case, the output characteristics of the MTI74 router will be as shown in FIG.

In addition to the ground clutter mentioned above, clutter also includes
There is clutter caused by reflections from rain and clouds. This web distortion may not be sufficiently suppressed by the MTI filter because the Doppler frequency may not be equal to rOJ. Therefore, in the past, the Doppler frequency of the target signal and these unnecessary signals such as noise and noise was different.

In view of this, a plurality of bandpass filters (hereinafter referred to as Doppler filters) having different passbands are connected in parallel after the M'rI filter, and the MTI filter output is further separated into different Dougler frequency bands. At the same time, we also attempted to detect each of these separated signals with an appropriate detection circuit, suppress the unnecessary signals among them, and then synthesize and reproduce them to extract the target signal mentioned above. There is. This method is generally called the JI/Russ Doppler method. Of course, the filtering characteristics of the above Doppler filter are K, as shown in FIG. 6 KR1 to Rn.
Each is set within the passband of the MTI filter.

It is well known that such wave behavior of each Doppler filter is achieved by applying FFT (Fast Fourier Transform) to consecutively received signals at the same distance. The method is MTI
Although this method can be praised in that it has become possible to suppress clutter more precisely than when suppressing clutter using only a filter, there are still many problems in practical use.

One of the most important examples is a zero-striped Doppler filter, whose respective passbands are preset on the assumption that the falsification intervals of the transmitted signal are equal.

However, in reality, in order to remove the unnecessary attenuation range caused by the MTI filter, it is necessary to employ the staggered trigger method described above to make the pulse intervals of the transmission signal unequal.

There are problems such as loss of received signal due to inconsistency between receivers and receivers. In other words, when a signal is transmitted using such a staggered trigger method, the shape of the above-mentioned puller filter is different from the design, and the transmission pulse interval is changed even for the received signal that is originally in the passband of the puller filter. A loss will occur due to the uneven spacing. Setting the transmission 19 pulse intervals to be unequal intervals is done without regard to such signal loss, and non-optimal staggered triggering is not necessarily performed in response to such loss.

[Purpose of the invention]

- This invention utilizes the above-mentioned staggered trigger method and p
An object of the present invention is to provide a radar signal transmission system that can minimize signal loss when performing received signal processing such as clutter suppression using a 4-Russ Doppler system.

[Summary of the invention]

In this invention, the 1? of the transmission pulse train is made irregularly spaced by a staggered trigger. The pulse interval is defined as an interval in which the difference between the time determined by the average pulse interval of all transmissions/mother pulses and the actual transmission time of each pulse is rOJ as an average value, and the root mean square value of each of these time differences is the minimum. Set it to . This means that even if the passband of each of the Doppler filters is set on the assumption that the pulse intervals of the transmitted signal are equal, the actual pulse intervals are unequal. This makes it possible to minimize the loss of these filter outputs.

[Embodiments of the invention]

First, the principle of this invention will be explained.

First, it is assumed that the reflected signal of the transmitted radar signal by the target is expressed by a function x (t), and furthermore, when the radar signal is received by the same radar device, this waveform is expressed as tn=to+(n+δn)...
(1) Suppose that the sample is sampled at a time of (1). Here, T indicates the average pulse interval of the transmitted radar signal, and δ. indicates the term caused by the uneven spacing of the same transmission pulses caused by the star trigger (usually ±0.05 to ±0.
(A value of about 2 is selected). Incidentally, the generation time of the transmission pulse is tn-2f%/CR: distance between the radar and the target C: speed of light.

Also, at this time, the reflected signal x (tl has a single frequency f
If it is expressed as K, then this waveform will be K as shown in the following equation.

X<t)=@XpCj2Kft)
・Mountain (2) Also, discontinuous 7-lier transform (DFT: Disoret@Fou) by sampling N points at equal intervals, which is used in normal Doppler filter design.
rier Transform) is generally given by the following equation.

Here, X(k) corresponds to the output of a band-pass filter whose center frequency is /NT. Incidentally, 1/1r of /NT usually corresponds to the above-mentioned nominal pulse repetition frequency PRF', and k/
N indicates the coefficient of multiplication of the PRF.

Now, if we calculate the same filter output The waveform
Losing the killing ability fi < t0 = = 0 and it can be frozen. X (k) shown in this formula (4) is the same as above (F)
It is the output of a bandpass filter (corresponding to the above-mentioned Doppler filter) whose center frequency is the frequency k/NT, and is particularly the output of the above (1 formula and (
It is defined by equation 2) and becomes the output of the same filter based on sampler time and reflected signal waveform.

Next, depending on the purpose of this invention, let's take a look at how much loss the filter output actually contains.

However, here, for the sake of simplicity, the output at the center frequency among the outputs of the same filter is determined, and attention is paid to the signal loss in the output at the center frequency. Of course, this does not lose its generality.

Therefore, first, by substituting f='/NT (5) for f in the above equation (4) and finding the output at this center frequency, the following equation is obtained.

Since this represents one complex number, δ, (
1, and by quadratic approximation for further simplification, the following equation is obtained.

According to Equation (7), the second and third terms represent the signal loss due to the transmission/fourth pulse intervals being unequal, and especially the third term represents the average This corresponds to the amount of deviation between the time determined by the pulse interval and the actual i4 pulse transmission time.

However, in this case, as is clear from the definition of equation (1) above, T is uniquely determined as the average value of the transmission norm intervals, so this amount of deviation is also ``0'' on average.
”, and in the end, this third term becomes , and the above equation (7) becomes: N--! −(2πヱ)2Y1δ2 ...(9)2
It is expressed as N n-On. Of course, in this equation (9), the second term is the signal loss due to the above-mentioned unequal transmission pulse intervals, and if a star like this is used for triggering, then It can be seen that this signal loss can be minimized.

In addition, in the conventional star trigger method, the transmission tJ? is given by the following equation. ) Several values that can be selected as the L/s interval Δtn (for example, 4 grains)
By preparing these in advance and using them in a fixed order, the stagger tree in question is realized.

Δtn = tn, -t n='l'+ (δn+1
-δn)T...C1OBy the way, this is the same as the previous fifth
This is determined by the requirements for the characteristics shown in the figure. Therefore, in order to realize the present invention in the simplest form, it is only necessary to set it so that the order of the transmission noise 1 interval values prepared in advance as the general □ is satisfied.

FIG. 1 shows an example of a radar device constructed based on such a principle, and an embodiment of the radar signal transmission system according to the present invention will be described below with reference to the same figure. However, in FIG. 1, the same elements as those of the radar device shown in FIG. Especially receiver 5
0, it is assumed that the received signal is processed using the pulsed Doppler method described above.

As shown in FIG. 1, this radar device includes a staggered trigger f device 70 consisting of a trigger interval setter 71, an order determining circuit 72, and a trigger generating circuit 73. The timing at which the transmitter 20 generates the above-mentioned transmission signal is determined by the generated trigger.

Here, the above-mentioned trigger interval setting device 71 means that, as explained in the previous principle, the difference from the average interval value is "0" at the average value, and several different trigger interval values based on the ClO formula are set. The ninth device to be set is the order determining circuit 72.
means that the root mean square value of the difference between the several birds set in this way and the average interval value (the value of T in the ClO formula) is the minimum based on the interval value, that is, (-N
,, [Lee ml・'' and n 0 are the same circuits that determine the arrangement order of interval values,
Then, the bird generation circuit 73 uses this determined arrangement order and each corresponding bird with an interval value to transmit the bird to the transmitter 2.
The circuit that controls the generation timing of the pulse signal (transmission at 0) is the circuit that generates the signal.

FIG. 2 shows an example of the signal generated in this way.

That is, in this example, the above bird is set to 6 by the interval setting device 71.
．． −δ2+δ, = 0 (T−δ,
), (T+δ, +δ2) # Four different birds such as ('r-δ2-δ3) and (T+δ3) have the interval value (
However, the arrangement order of these birds is undetermined at this stage), and the order determining circuit 72 determines the root mean square value of the difference δn (n = 1.2°3) between the interval value and the average interval value T. The order in which the interval values are arranged is determined for the same trigger shown in FIG. This example shows a case where a signal (indicated by a thick line) is generated. The signals formed and generated in this way cause the transmission pulse signal to be star-strapped by the signal. Signal loss can be minimized.

In addition, in this embodiment, a method is adopted in which several values that can be selected as the transmission pulse interval given by the Mata Q equation are set in advance, and then the arrangement order of these values is determined. The difference between the value and its average value is ``
0'' and that the root mean square value of these difference values is the minimum, as long as the staggered trigger can form a signal, other, but not limited to,
Of course, any method may be used.

〔Effect of the invention〕

As described above, the radar signal transmission system according to the present invention employs the t4 Luss Doppler system, which is convenient for performing fine-grained suppression of various types of clutter. A radar device that employs a trigger method has a star that is preferable for removing unnecessary attenuation regions, and effectively minimizes the loss of the Doppler filter output caused by the unequal transmission pulse intervals due to the stagger trigger. It is possible to limit it. As a result, a high-performance radar device can be realized in which only the advantages of the pulse Doppler one-way system and the staggered trigger system are effectively utilized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a radar device used in an embodiment of the radar signal transmission system according to the present invention, and FIG.
The figure is a timing chart showing an example of a staggered trigger signal (transmission radar signal) used in the radar signal transmission system according to the present invention, FIG. 3 is a block diagram showing the configuration of a general radar device, and FIG. 4 is a general MTI filter. Figure 5 is a diagram showing an example of the output characteristics of an MTI filter when a staggered trigger method is adopted for transmitting radar signals, and Figure 6 is a diagram showing an example of the output characteristics of an MTI filter using a pulse Doppler method. FIG. 3 is a diagram showing an example of characteristics. 10... High frequency oscillator, 20... Transmitter, 30...
・Transmission/reception switch, 40... antenna, 50... receiver,
60...Display device, 7o0.・Star ga tori ga device, 71
... Tori is an interval setter, 72 ... Sequence determining circuit, 7
3...Tri is generated circuit T-÷-T + T-→-T← S, -S2+chi=0 Fig. 2

Claims (1)

[Claims] A plurality of bandpass filters with different passbands are arranged in parallel corresponding to a frequency range determined by the reciprocal of a specific transmission pulse interval, and a reflected signal of a radar signal transmitted to a target is received. In a radar signal transmission method of a radar device that suppresses unnecessary signals based on the selection of these filter outputs during processing, the transmitted radar signal includes a time determined by the average pulse interval of all transmitted pulses and an actual pulse transmission time. A radar signal transmission system characterized by using a pulse signal that is staggered at a transmission pulse interval in which the average difference between the two time differences is "0" and the root mean square value of each of these time differences is the minimum.