JPS6044882A - Deviation frequency measuring apparatus - Google Patents

Abstract

PURPOSE:To measure deviation frequency on a real time basis, by a small light wt. apparatus having such a mechanism that the beat signal of a received linear frequency modulating signal and a signal obtained by delaying said signal over a predetermined time is generated and a number of zero cross times are counted. CONSTITUTION:A delay linear FM signal (b) delayed over a predetermined time by a delay wire 1 and a non-delay linear signal (a) are inputted to a mixer 2 to generate an output mixture containing a beat signal. The output mixture is passed through a video amplifier 3 to extract only the beat signal component and a number of zero cross times thereof are counted by a zero cross counter 4. An operator 8 operates and outputs the deviation frequency of the linear FM signal (a) on the basis of the count number of the zero cross counter 4 and the pulse amplitude of the linear FM signal due to a pulse amplitude amplifier 7.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is designed to receive a pulse compression radar signal transmitted by a linear frequency modulation method (linear FM/chirb method) and measure its shift frequency. The present invention relates to a deviation frequency measuring device.

(Prior art) In recent years, there has been a tendency for pulse compression radars to be used frequently, which provide excellent characteristics in terms of distance resolution and sensitivity.
Military radar warning systems, etc., receive pulse compression radar signals emitted by multiple radars belonging to the opponent type, classify each radar signal by its emission source, and then classify the type of each emission source, such as the purpose of the radar. It is necessary to estimate.

Conventional classification/classification methods for this purpose use specifications such as the carrier frequency and pulse width of the received radar signal, but this is insufficient for pulse compression radars, and the pulse compression ratio unique to pulse compression radars is insufficient. Alternatively, it is necessary to measure the deviation frequency and use this. However, conventionally, there is no pulse compression ratio or deviation frequency measurement device that can classify pulse compression radars into launch-end types and estimate their uses.

Now, if we consider the requirements for a military radar υ control device for pulse compression radar, we will find the following.

First, military radar warning systems usually receive transmission pulses from multiple radars at the same time, so pulse trains from different emission sources are interleaved with each other.
e) will receive the pulse train. Therefore, in order to classify each pulse constituting this pulse train into a firing end, it is necessary to measure the pulse compression ratio or shift frequency of each pulse.

On the other hand, in an interleaved pulse train, the next pulse may arrive immediately after one pulse arrives.
Therefore, it is required to complete the measurement of one pulse during the period (within the pulse width) during which the pulse is being received, and to prepare for the measurement of the next pulse that arrives immediately after.

Furthermore, in military radar warning devices that are mainly installed on small aircraft such as fighter jets, it is strongly desired that the measuring device be small and lightweight.

(Object of the Invention) The present invention has been made in view of the above situation, and is based on a pulse compression radar that employs a linear frequency modulation method among pulse compression radar signals, that is, a chirp radar (Chirp'rad).
A deviation frequency measuring device that can measure in real time the deviation frequency corresponding to each pulse received by interleaving, and which can be made smaller and lighter as a measuring device. The purpose is to provide

(Structure and operation of the invention) In order to achieve this object, the present invention generates a beat signal consisting of a received linear frequency modulation signal and a signal obtained by delaying this signal by a predetermined time, and detects the frequency of zero crossings based on the number of zero crossings of this beat signal. The shift frequency of a linear frequency modulation signal is calculated.

(Embodiment) FIG. 1 is a circuit block diagram showing an embodiment of the present invention.

- First, to explain the configuration, numeral 1 is a delay line having a delay time τ, into which a linear FM signal a is input as an IF output of a received jab radar signal. 2 is a mixer which inputs the delayed linear FM signal delayed by the delay line 1 and the non-delayed linear FM signal a, and produces a mixed output containing a beat signal component.

3 is a video amplifier which amplifies only the root frequency band (low frequency band) and removes high frequency components such as IF acid components contained in the mixed output. A zero-cross counter 4 counts the number of zero-crosses of the beat signal C output from the video amplifier 3 by h1.

On the other hand, 5 is a threshold detector which detects and outputs the envelope of the linear FM signal @a which exceeds the threshold level. 6 is a gate signal generation circuit, which connects the delay line 1 from the rising edge of the detection output of the threshold detector 5.
After a delay time τ equal to the delay time τ, the gate signal @d is generated, and when the detection output of the threshold detector 5 falls, the output of the signal d is stopped. A pulse width detector 7 inputs the detection output of the threshold detector 5 and outputs a signal, for example, a digital signal, having information on the pulse width T of the linear FM signal a.

8 is an arithmetic unit, and the numbers 1 to 8 of the zero cross counter 4
Given the number N and the pulse width T of the linear FM signal @a from the pulse width detector 7, the deviation frequency ΔF of the linear FM signal is calculated and outputted through calculation processing that will be explained later.

FIG. 2 shows the signals of each part and their temporal relationships in the embodiment of FIG. 1, and FIG. 2(a) shows the delay line 1.
．． A linear FM signal a input to the mixer 2/f3 and the threshold detector 5 is shown, and the frequency changes linearly from fO to fO+ΔF during the pulse width T. Here, ΔF
is the deviation frequency. Figure 2 (b) shows the delayed linear FM signal (b) output from delay line 1, and Figure 2 (C
) shows the beat signal C obtained by mixing the non-delayed linear FM signal a and the delayed linear FM signal outputted from the video amplifier 3, and (d) of the same figure shows the beat signal C obtained by mixing the non-delayed linear FM signal a and the delayed linear FM signal outputted from the video amplifier 3. The gate signal d from the gate signal generator 6 is shown.

In addition, Fig. 3 shows the non-delayed linear FM signal a and the delayed linear FM signal a.
M shows how the frequency of the signal changes over time, a
This shows that the frequency difference (beat frequency) fb between and b is constant, and the connection period of a is (T-τ).

Next, the operation of the embodiment shown in FIG. 1 will be explained together with the principle of measuring the deviation frequency ΔF.

First, it is assumed that the input signal @a in FIG. 1 is, for example, the output of a 1F amplifier, and the frequency changes linearly from fO to fO+ΔF during the pulse width T, as shown in FIG.

On the other hand, since the delayed linear FM signal from delay line 1 is a signal 2Z obtained by delaying the non-delayed linear FM signal a by a certain time τ, the mixed output of mixer 2 is fb=ΔF(τ/T) (1
) is included, which is the beat frequency fb given by . Of course, the frequency components higher than the beat frequency f6 than mixer 2,
For example, the IF acid component is output, but the next stage video amplifier 3
Since video amplifier 3 has the function of amplifying only the beat frequency band, the beat signal @C of frequency fb is better than video amplifier 3.
is obtained.

Therefore, if the frequency fb of this beat signal is measured, the pulse width T can be measured separately using the pulse width detector 7.
Further, since τ is a circuit constant, the deviation frequency ΔF can be determined by the following equation.

ΔF=f&, (T/τ) (2) However, in order to measure the beat signal frequency ``T'', the circuit configuration becomes complicated and is insufficient for military radar g-force equipment, which requires compact pumice. Therefore, in the present invention, instead of measuring the frequency fb of the beat signal, a device configuration is adopted that counts the number of times the beat signal changes polarity, that is, the number of times the beat signal crosses zero volts. The number of times zero volts are crossed will be described as zero crossing number N.

That is, in order to count the number of zero-crossings N of the beat signal C, the output of the video amplifier 3 is input to a zero-crossing counter 4, and the control terminal of the zero-crossing counter 4 is connected to the period during which the P1-signal C exists and the counting operation. In order to prevent noise from being counted during other periods, the gate signal generator 6 outputs signals only during the generation period of signals B1 to C.
A gate signal d is applied to allow the counter operation. Note that the zero cross counter 4 is reset at the rise of the gate signal d.

Therefore, to explain in detail the measurement of the frequency deviation ΔF based on the number of zero crossings N of the beat signal, first, we will explain in detail the measurement of the frequency deviation ΔF based on the number N of zero crossings of the beat signal.
), the polarity of the beat signal is reversed twice per cycle on average, and the duration is (T-), so the number of zero crossings N is approximately given by N = 2fb (T-τ) (3) . Note that since the count of N is an integer, formula (3) is approximated to take muntinization errors into account. Therefore, the beat frequency fb can be approximated by the following equation.

f) −: N/2 (T−τ) (4) This (4)
By substituting the equation into the above equation (2), the desired frequency deviation Δ
F is approximately given by ΔF”N (T/2r (T-r)) <5). In this equation (5), the delay time τ is given as a circuit constant, and the pulse width T is the pulse width Width detector 7
Since the above equation (5) is obtained by
The deviation frequency ΔF of the linear FM signal is
can be used.

This J: Uni, if the deviation frequency ΔF of the linear FM signal is known, the pulse width after pulse compression in the radar is 1/ΔF.
Since it corresponds to , the resolution of the chirp radar can be determined. In summary, since 1/ΔFT gives the pulse compression ratio, it is also possible to know the pulse compression ratio of the radar.

In the embodiment described in "-", the operator 8 is used to derive an approximate value of the deviation frequency ΔF from the equation (5), but the number of zero crossings N is N=ΔF (2r (T -r)
/T) (6) Since it is a function of ΔF, which is a specification of the radar, and the king, this N itself can be considered as a specification specific to the radar and used for classification of emission sources, etc.

In this case, the arithmetic unit 8 and pulse detector 7 can be omitted.

(Effects of the Invention) As explained above, according to the present invention, a pulse compression radar using a linear frequency modulation method is targeted, and a received linear frequency modulation signal and a signal obtained by delaying this signal by a predetermined time are Since a beat signal is generated and the deviation frequency is determined based on the number of zero crossings of this beat signal,
It is difficult to measure signals from multiple chirp radars that differ only in shift frequency or pulse compression ratio, which is difficult with conventional carrier frequency and pulse width measurements.
Furthermore, it becomes possible to estimate the type of each emission source, for example the use of radar. Furthermore, even if pulse trains from different emission sources are received interleaved with each other, the measurement of the deviation frequency for one pulse can be completed within the period (within the pulse width) during which that pulse is being received. It is possible to prepare for the shift frequency of the next pulse arriving immediately after, and to measure the abbreviated real-time 'C' shift frequency even for radar signals from multiple sources, thus:
This made it possible to classify these as launch-segiri.

Furthermore, since the circuit components that make up the measuring device do not require large volume or weight, the measuring device can be made small and lightweight, and is mainly installed in small aircraft such as fighter jets. It has high practical value as a military radar warning device.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, FIG. 2 is a timing chart showing the signals of each part and their mutual time relationships in the embodiment of FIG. 1, and FIG. FIG. 3 is a graph diagram showing the generation of a beat signal in terms of frequency versus time axis in the example. 1: Delay line 2: Mixer 3: Video amplifier 4: Zero clock f] Counter 5: Threshold detector 6: Boot signal generator 7: Pulse width detector 8: Arithmetic circuit Patent applicant Tokyo Keikidai Shinshin Co., Ltd. Patent attorney Takeuchi Arrest Proceedings Masayoshi Ichi (Voluntary) Commissioner of the Japan Patent Office Kazuo Wakasugi 1. Indication of the case Patent Application No. 152670 filed in 1982. 2. Name of the invention Shift frequency measuring device 3. Person making the amendment. Relationship with the case. Patent applicant address 2-16-46 Minami Kamata, Ota-ku, Tokyo Name <
338) Tokyo Keiki Co., Ltd. 4, Agent address: 4th floor, Nishi-Shinbashi Chuo Building, 3-15-8 Nishi-Shimbashi, Minato-ku, Tokyo Column 6 of the detailed explanation of the invention in the specification, page 7 of the detailed description of the amendment In the 15th line, replace "its connection period" with "
Its duration period” is corrected. Above Procedure 11i-tE (spontaneous) February 10, 1980 Patent Application No. 152670 of 1988 2 Name of the invention Shift frequency measuring device 3 Relationship with the Ministry case for amendment Patent applicant address Tokyo 2-16-46 Minami Kamata, Ota-ku, Tokyo Name (
338) Tokyo Keiki Co., Ltd. 4, Agent A 4th floor, Nishi-Shinbashi Chuo Building, 3-15-8 Nishi-Shimbashi, Minato-ku, Tokyo Column 6 of ``Detailed explanation of the invention'' in the specification 1980 Contents of the amendment "Duration period" on page 7, line 15 of the specification, which was amended in the procedural amendment submitted on October 13th, is amended to "duration period."that's all

Claims (1)

[Claims] In a shift frequency measuring device that targets a pulse compression radar signal transmitted by a pulse compression radar using linear frequency modulation, a signal obtained by delaying the received linear frequency modulation signal and the modulated signal by a predetermined time is used. A signal generating means for generating a beat signal, a counting means for dividing the number of zero crossings of the beat signal obtained by the beat signal generating means, and a linear frequency modulation based on the zero crossing count value of the counting means. 1. A deviation frequency measuring device comprising: calculation means for calculating a frequency deviation of a signal.