JPS6147578A - Doppler radar equipment - Google Patents

Abstract

PURPOSE:To improve the S/N ratio with a larger pulse width of a transmission signal, by extracting a Doppler signal output always using the entire range of the continued time of a received signal disregarding distance. CONSTITUTION:A reflected signal from an object to be measured is inputted into a homodyne detector 6 and a locally generated signal input into the detector 6 is a continuous signal wave which is fetched by branching the output of a high frequency transmitter 1. The homodyne detection output is delayed but a Doppler signal with the entire width of the transmission signal pulse is obtained. A sampling circuit 11 detects the input signal level at the time delayed from the rising time of the transmitted pulse through a sampling pulse generation circuit 10 which generates a pulse delayed by a fixed time from the rising time of a pulse generation circuit 8. A sampling output is judged on the level with a judging circuit 12 and acts to conduct an analog switch 13 when the absolute value thereof exceeds a reference level. The output of the analog switch 13 is taken out through the output of a lowpass filter 7 to obtain a Doppler signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention utilizes the Doppler effect of radio waves to measure the speed of vehicles, etc., and uses pulse modulated waves to measure the speed of objects within a certain distance. This relates to a Doppler radar device that measures only objects.

Conventional configuration and its problems A conventional pulse modulation system has a configuration as shown in FIG. 1, for example. The operation will be explained below using the waveform diagram shown in FIG.

In Fig. 1, 1 is a high frequency oscillator, 2 is a pulse modulation circuit, 3 is a brancher, 4 is a circular loop, 5 is a transmitting/receiving antenna (antenna), 6 is a homodyne detector, 7 is a low-pass filter, and 8 is a clock. The generating circuit 9 is a pulse generating circuit. Further, 8 to 8e are signals of various parts, and an example of their waveforms is shown in FIG.

Next, the operation of the above conventional example will be explained. Continuous transmission of high frequencies (e.g. microwaves or millimeter waves) generated by the high frequency oscillator 1 is outputted by the pulse modulation circuit 2 only during the period tl, and the rest of the time is in the 5 trillion signal state, which is transmitted at the period of t4. It is an intermittent wave that repeats. This intermittent wave is transmitted from the antenna 5 through the circulator 4, reflected by the object to be measured, and received by the antenna again. This received signal is subjected to a Doppler shift proportional to the speed of the object to be measured, so when it is mixed with a part of the transmitted signal extracted by the splitter 3 in the homodyne detector 6, the Doppler component is output as a signal. be done. At this time, if the distance between the antenna and the object to be measured is R1 and the speed of the radio wave is C, the envelope of the received signal is the envelope of the transmitted signal. The Doppler signal e is extracted by passing it through a low-pass filter. Therefore, as the distance between the antenna and the object to be measured increases, the envelope lines of the transmitted wave and the received wave no longer overlap, so it is possible to limit the maximum value of the measurable distance. This measurement can be done.

However, in the above conventional example, tl measurement limit distance IC
If an attempt is made to reduce Rm by l, the width t1 of the puffless will also become smaller, making it difficult and expensive to manufacture the pulse modulation circuit. Also, if the pulse repetition period is shortened, the occupied band of the modulated wave becomes wider, so the period t4 cannot be made too short, and the ratio of the time t5 during which the Doppler signal is actually detected to the period t4 becomes small. , the energy of the extracted Doppler signal eventually decreases and the signal's S/
N is much worse than that of continuous wave Doppler radar. Further, in order to secure the necessary S/N ratio, t5 must have a certain width or more, but the size of this time width changes depending on the magnitude of the reception level. In other words, if the object to be measured is large, the time width t5 required for measurement will be small, and if the object to be measured is small, the required S/N will not be obtained unless the time width t5 is increased by the small size of the received signal. . Therefore, the measurement limit distance is not only actually shorter than the above-mentioned calculated value, but also has the disadvantage that it varies depending on the size of the object to be measured.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the above-mentioned conventional examples.
It is an object of the present invention to realize a Doppler radar device that can obtain a Doppler signal with a good /N and has little variation in measurement limit distance depending on the size of an object to be measured.

Structure of the Invention In order to achieve the above object, the present invention determines whether the distance to the object to be measured exceeds the measurement limit distance based on the presence or absence of a Doppler signal after a certain time after the rising time of the sending signal pulse. , Doppler signals make it possible to widen the pulse response width of the transmitted signal, improving the S/N ratio, and detecting the distance limit using the voltage level sampled over a fixed short time span. This has the effect of reducing the variation in the measurement limit distance due to the size of the distance.

Description of examples Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows the ('ilj configuration) of one embodiment of the present invention, where 1 to 9 are the same as the conventional example shown in FIG. 11 is a sampling circuit, 12 is a determination circuit that determines the level of the sampling output, and 13 is an analog switch. Fig. 4 shows the signal waveforms of each part in Fig. 3. shows.

Next, the operation of the above embodiment will be explained. The high frequency signal output is modulated by the pulse modulation circuit 2 and sent from the antenna, and the reflected signal from the object to be measured is input to the homodyne detector 6, as in the conventional example shown in FIG. This differs from the conventional example in that the local signal input to the oscillator is a continuous signal wave extracted from the output branch of the high-frequency oscillator 1, and is not an intermittent pulse modulated signal. therefore,
Although the homodyne detection output is delayed by tl as shown in FIG. 4C', a Doppler signal is obtained during the entire pulse width t1 of the output signal. This homodyne detection output is input to the analog switch circuit 13 and the sampling circuit 11. The sampling circuit 11 detects the input signal level in a short time span at a time delayed by the time υ t5 from the rising time of the sending pulse. At this time t5, the measurement limit distance is Rm, and the sampling output undergoes a level judgment in the judgment circuit 12, and when the absolute value is equal to or higher than the reference level set to a value larger than the noise level, the next sampling pulse Make sure to keep the analog switch 13 conductive until just before the voltage rises.

The output of the analog switch 13 is taken out through the output of the low-pass filter 7, and a Doppler signal is obtained. In this way, the pulse width t1' of the transmitted signal is not limited by the measurement limit distance Rm, and it is only necessary to be careful not to overlap the next pulse due to reflection from a further distance. Therefore, 1,/ can be made sufficiently larger than tl in the conventional example. Also, the homodyne detection output is tl
Since the signal can be extracted over the entire width (t7 = tt' + t2 - ts t6), the energy of the signal that can be extracted is very large compared to the conventional example, and the S/ N does not drop; rather, when the distance is short, that is, the smaller tl is than ts, the detectable time width t7 becomes smaller, but the shorter the distance, the higher the received signal level becomes, so as a result, the S/N becomes lower. It is convenient because it does not fall off.

Also, the judgment itself of distance II: is a constant thin pulse width t.
Since the detection is performed using the homodyne detection output voltage sampled at the time 6, there is less possibility that the detection position will shift depending on the size of the object to be measured. Furthermore, since the setting of the limit distance is determined only by the setting of the delay time t5 of the sampling pulse, the measurement limit distance can be changed without changing the high frequency part.

Effects of the Invention The present invention has the structure described above, and it is possible to manufacture a Doppler radar device with a good S/N ratio with a small high-frequency transmission output, so the cost is low. Since the variation in the limit distance is reduced, the reliability of the device is improved9.Furthermore, since the distance can be set regardless of the high frequency part, a Doppler radar with a variable measurement limit distance can be realized at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example of a pulse modulation Doppler radar, FIG. 2 is a signal waveform diagram of each part thereof, FIG. 3 is a block diagram of a Doppler radar device according to an embodiment of the present invention, and FIG. The figure is a signal waveform diagram of each part. 2... Modulation circuit, 5... Antenna, 6...
...homodyne detector, 11...sampling circuit, analog switch. Name of representative Patent attorney Toshi Nakao Haga 1 person 2nd person
Figure 3, da

Claims (1)

[Claims] a pulse modulation circuit for pulse-modulating a high-frequency signal and transmitting it from an antenna, and receiving a signal received from the antenna as input;
a homodyne detector which receives continuous high frequency waves before being pulse modulated as a local oscillation input; a sampling circuit which samples the output of the homodyne detector after a fixed time from the rise time of each modulated pulse; A Doppler radar device comprising an analog switch that conducts the output of the homodyne detector for a certain period of time when the absolute value becomes larger than a reference level.