JP5019994B2 - Equivalent time sample radar system - Google Patents

Description

The present invention relates to an equivalent time sample the radar equipment.

  In a general pulse radar device, a rectangular wave or a pseudo rectangular wave (hereinafter referred to as “wave packet pulse”) modulated by a carrier wave is transmitted, and the transmitted wave packet pulse signal is reflected or scattered by the target, The distance is calculated based on the round-trip propagation time until the wave packet pulse is received. For example, Patent Document 1 discloses an equivalent time sampling in which a pulse is periodically transmitted repeatedly and sampling is performed at a time offset for each period with respect to a reception pulse received by reflecting each pulse at a target. Discloses a method of extending the same waveform as the received pulse on the time axis.

  On the other hand, Patent Document 2 discloses a method of detecting the rising edge of a pulse so as to enable distance measurement with a time resolution shorter than the pulse width and wavelet pulse width. Patent Document 3 discloses a method of transmitting a signal obtained by amplitude-modulating laser light with a signal obtained by determining a linear frequency modulation signal with a threshold value.

Japanese National Patent Publication No. 8-509110 JP 2002-365362 A JP-A-7-35857

  However, in any of the above Patent Documents 1, 2, and 3, it is difficult to increase the distance resolution when using a wave packet pulse having a narrow occupied bandwidth and a slow rising speed.

  Accordingly, an object of the present invention is to enable distance measurement with high resolution (short time resolution) even when the wave packet pulse width to be transmitted and received is long and the rise is slow.

In order to solve such a problem, in the present invention, a transmission system that radiates a wave packet pulse that is a rectangular wave or a pseudo-rectangular wave modulated by a carrier wave, and is radiated from the transmission system to the outside and reflected or scattered by a target. to have a a receiving system for receiving a received pulse by the receiving antenna wave packet pulses from the received target to provide an equivalent time sample the radar device. Receiving system includes a receiving pulse, by performing convolution based on a sample pulse is a square wave or pseudo-rectangular wave having a pulse width that matches the one cycle time of the carrier wave of the wave packet pulses, equivalent time for the received pulses Sampling is performed .

  When a periodic wave such as a sine wave is integrated over one period, the positive value and the negative value cancel each other and theoretically become zero. The output waveform of the equivalent time sampling is a waveform obtained by performing convolution integration between the received signal and the sampling waveform. If the sampling waveform is a rectangular wave that coincides with the period of the wave packet, the part having the positive value and the part having the negative value cancel each other out in the part where the wave packet exists over one period. When the width of the sample pulse is made to coincide with the period time of the carrier wave, as shown in FIG. 2, the part where the envelope of the received pulse is flat in one part of the carrier wave period is caused by the integration effect of the sample pulse. The positive and negative parts are erased from each other. This effect makes it possible to emphasize the rising and falling edges of the received pulse.

Here, in the present invention, the reception system preferably includes a sample pulse generation unit, a sample hold circuit, and a pulse shaping unit. The sample pulse generator generates a sample pulse having a pulse width that matches one cycle time of the carrier wave of the received pulse. The sample hold circuit holds the voltage of the received pulse according to the timing of the sample pulse and outputs a sample signal. Pulse shaping unit is provided between the sample-and-hold circuit, so that the sample pulse generator is steep rising and falling of the output to Rusa Npuruparusu waveform shapes the sample pulse.

In the present invention, the receiving system further includes a band-pass filter provided between the receiving antenna and the sample hold circuit, and an amplifier that amplifies the sample signal among the sample signals output from the sample hold circuit. Also good. The frequency of the fundamental wave of the sample pulse is preferably ½ of the frequency of the carrier wave of the received pulse.

Further, in the present invention, sample and hold circuit, an input terminal, an output terminal, and a sample pulse ends, the switching element is a first impedance element, a capacitor, a reactance element is a second impedance element It is preferable to have . An input signal to be sampled is input to the input end. An output signal after sampling processing is output to the output end. A sample pulse defining a sampling time is supplied to the sample pulse end. The switching element has one end connected to the sample pulse end and the other end connected to the output end. The capacitor has one end connected to the output end, the other end connected to the input end, and integrates the voltage of the input signal for the duration of the sample pulse. After the sample pulse ends, the input signal Holds the integral of the voltage. The reactance element has one end connected to the capacitor and the input end, and the other end is grounded. The reactance element has a high impedance when viewed from a high frequency signal, and has a low impedance for a direct current and a low frequency signal. This sample and hold circuit realizes a sample and hold circuit in which a positive part and a negative part are erased from each other with respect to a part where the envelope of the received pulse exists over one period of the carrier due to the integration effect of the sample pulse. Is.

Here, in the present invention, the switching element has a high impedance when the sample pulse is at the first level, causes the capacitor to hold the input signal, and when the sample pulse is at the second level different from the first level, A semiconductor switch element having low impedance is preferable. The reactance element is preferably a coil having a high impedance with respect to the frequency of the input signal and a low impedance with respect to frequencies other than this frequency.

In the present invention, the sample and hold circuit may be further provided with a low-pass filter provided between the input terminal and the capacitor. In this case, the second impedance element is preferably a coil included in the low-pass filter.

According to the present invention, in a portion where an envelope exists over one period of a carrier wave, a portion having a positive value and a portion having a negative value cancel each other. When the received signal is a wave packet that is a rectangular wave or pseudo-rectangular wave modulated by a carrier wave, the rising and falling of the wave packet Can be extracted effectively. As a result, distance measurement with high resolution (short time resolution) is possible even when the wave packet pulse width to be transmitted and received is long and the rise is slow.

  First, the principle of the embodiment of the present invention will be described. FIG. 2 is an explanatory diagram of the sample pulse and illustrates the relationship between the pulse width of the sample pulse and the shape of the sample signal. FIG. 5A is a diagram showing a case where the pulse width of the sample pulse is equal to or less than ½ cycle time of the received pulse, which is conventional sampling. In the conventional sampling, the half-value width (width at half of the peak height) is made as short as possible in order not to destroy the waveform of the received pulse, that is, to ensure the reproducibility of the waveform of the received pulse.

  On the other hand, FIG. 5B shows the sampling according to the present embodiment, and shows the case where the width of the sampling pulse is one cycle time of the received pulse. Since the sampling pulse is as long as one cycle time, the rising portion of the received pulse is reflected in the rising portion of the sample signal. Further, the intermediate portion of the sample signal takes a value close to 0 because it is integrated by the sample pulse. As a result, the envelope of the received pulse after the equivalent time sampling is differentiated, and the rise and fall of the end of the envelope become steep.

  FIG. 3A shows a simulation result by a circuit simulator that outputs a sample signal by arbitrarily setting a pulse width of a sample pulse for a narrow-band received pulse. In this case, the shape of the sample signal is different from the shape of the original received pulse. FIG. 6B shows a simulation result by a circuit simulator for a sample signal sampled with a pulse width of a conventional sample pulse (less than 1/2 cycle time of a received pulse). The sample signal in this case substantially maintains the original received pulse shape. FIG. 4C shows a sample signal sampled with the pulse width of the sample pulse of this embodiment (one period time of the received pulse). The sample signal in this case is differentiated from the original envelope waveform of the received pulse shown in FIG.

FIG. 1 is a configuration diagram of an equivalent time sample radar according to an embodiment of the present invention. The equivalent time sample radar is composed of a transmission system and a reception system. The transmission system includes a transmission pulse generation unit 1 and a transmission antenna 2, and radiates transmission pulses generated from the transmission pulse generation unit 1 to the outside via the transmission antenna 2. On the other hand, the reception system includes a reception antenna 3, a sample pulse generation unit 4, a sample hold circuit 6, a pulse shaping unit 5, a band pass filter 7, an amplifier 8, and a distance measurement unit 9. The principal features of this embodiment, on the basis of the sample pulse with Rupa pulse width to correspond to one period time of the carrier frequency of the received pulse lies in performing sampling of a received pulse.

Of the wave packet pulse emitted from the transmission antenna 2 to the outside, the wave packet pulses reflected or scattered by the target T to be Ranging object is received by the receiving antenna 3 as a reception pulse. The sample pulse generation unit 4 generates a sample pulse having a pulse width corresponding to one cycle time of the carrier wave of the wave packet pulse. The sample hold circuit 6 integrates the voltage of the input signal while the sample pulse continues, and after the sample pulse ends, holds the integrated value of the voltage of the input signal and outputs the sample signal.

  The pulse shaping unit 5 is provided between the sample pulse generation unit 4 and the sample hold circuit 6 so that the rise and fall of the waveform of the sample pulse signal output from the sample pulse generation unit are steep. Shape the sample pulse.

  The band pass filter 7 is provided between the reception antenna 3 and the sample hold circuit 6. The band pass filter 7 is provided in order to prevent unnecessary electromagnetic waves from being radiated to the outside via the receiving antenna 3. From this point of view, it is preferable that the frequency spectrum of the sample pulse is set so as not to overlap with the frequency spectrum of the received pulse.

  The amplifier 8 is provided on the output side of the sample and hold circuit 6 and amplifies the sample signal output from the sample and hold circuit 6. The distance measuring unit 9 detects the rise of the sample signal amplified by the amplifier 8 and calculates the distance to the target T. For example, the voltage 0 is set as a threshold value, and when a sample signal higher than the threshold value is detected, the presence of the target T is confirmed and the distance is measured.

  The sample hold circuit 6 performs convolution integration based on the received pulse and the sample pulse to obtain a sample value constituting a part of the sample signal. Then, the sample pulse generator 4 sweeps the sample pulse with time, so that a sample signal composed of sample values corresponding to the time sweep is output from the sample hold circuit 6.

  FIG. 4 is a configuration diagram as an example of the sample and hold circuit 6. The sample hold circuit 6 includes three end points (input end, output end, pulse end), a switching element 6a, a reactance element 6c, and a capacitor 6b. The input end is connected to the receiving antenna 3 side (more precisely, the band pass filter 7), and an input signal which is a reception pulse to be subjected to sampling processing is input. The output end is connected to the distance measuring unit 9 side (more precisely, the amplifier 8), and an output signal which is a sample signal after sampling processing is output. The pulse end is connected to the sample pulse generation unit 4 side (more precisely, the pulse shaping unit 5), and a sample pulse that defines the sampling time is supplied. The switching element 6a has one end connected to the sample pulse end and the other end connected to the output end. The capacitor 6b has one end connected to the output end and the other end connected to the input end. The capacitor 6b integrates the voltage of the input signal while the sample pulse continues, and maintains the integrated value of the voltage of the input signal after the sample pulse ends. The reactance element 6c has one end connected to the input end and the other end grounded. The reactance element 6c has high impedance for high-frequency signals and low impedance for DC and low-frequency signals.

  At this time, the high impedance is ideally a state where the impedance is infinite (∞) and there is no reactance element 6c. The low impedance is ideally a state in which the impedance is 0, the reactance element 6c is not present, and the input terminal and the ground (ground) are short-circuited.

  When the sample pulse is on, the voltage of the sample pulse itself and the voltage of the input signal are convolved, and the convolved voltage is stored in the capacitor 6b. At this time, the reactance element 6c has a high impedance when viewed from the input end to which a high-frequency signal is input, and the voltage of the input signal is efficiently stored in the capacitor. In addition, the impedance is low for DC and low frequency signals. The voltage held in the capacitor is transmitted to the output terminal as an output signal. The amplifier 8 amplifies the low frequency equivalent time sampled output signal.

  FIG. 5 is a configuration diagram as a modified example of the sample and hold circuit 6. In FIG. 6A, the switching element 6a is a resistance element, and the reactance element 6c is a coil. In the case of this configuration, the voltage of the sample pulse requires the loss of the resistance element.

  In the configuration shown in FIG. 5B, the switching element 6a is a semiconductor switching element such as a diode, and the reactance element 6c is a coil. In this case, the input signal frequency (high frequency) is high impedance (no coil), and other frequencies, for example, the output signal frequency is low impedance (coil is ground shorted). Become. In the configuration of FIG. 5C, the switching element 6a is a switching element that switches on / off in accordance with the sample pulse, and the reactance element 6c is a resistance element. When the sample pulse is at the H level, the switch has a high impedance (a state in which there is no pulse end from the switch element), and the capacitor 6b holds the input signal. When the sample pulse is at the L level, the switch has a low impedance (the switch element is It is a state of a conducting wire with no loss). In these cases, the sample signal is lost by the resistance element.

  In the configuration of FIG. 4D, the switching element 6a is a switch similar to that of FIG. 4C, and the reactance element 6c is a coil similar to that of FIG. Further, in the configuration of FIG. 5E, the switching element 6a is a switch similar to that of FIG. 5C, the reactance element 6c is a coil similar to that of FIG. 5B, and the input signal side (input end) , And a coil of a low-pass filter provided between the capacitor 6b and the capacitor 6b. In this case, since the low-pass filter reduces the leakage of the sample pulse to the input signal side (input end), the radiation amount of the leaked radio wave from the receiving antenna 3 connected to the input signal can be reduced. In particular, by setting the occupation band of the sample pulse so as not to overlap with the occupation band of the input signal, it is possible to further reduce the emission of leaked radio waves due to the sample pulse.

  As described above, according to the equivalent time sample radar according to the present embodiment, when the sampling pulse is as long as one cycle time, the rising portion of the received pulse is particularly as shown in FIG. 2B and FIG. In the sample signal, it is reflected as a sudden rise. Therefore, the distance measuring unit 9 that measures the distance to the target T based on the sample signal can extract the rising of the wave packet early and effectively, and is a case of a received pulse with a slow rising speed in a narrow band. However, distance measurement can be performed with high resolution (short time resolution).

  The sample and hold circuit described in U.S. Pat. No. 5,345,471 has a large number of devices, and voltage loss occurs due to matching resistors, filters, and the like. On the other hand, since the sample and hold circuit 6 of this embodiment does not require many devices, voltage loss caused by them can be suppressed, and efficient sampling can be performed.

Equivalent time sample radar configuration diagram Illustration of sample pulse Illustration of sample pulse simulation Configuration diagram as an example of sample and hold circuit Configuration diagram as a modification of sample hold circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission pulse generation part 2 Transmission antenna 3 Reception antenna 4 Sample pulse generation part 5 Pulse shaping part 6 Sample hold circuit 6a Switching element 6b Capacitor 6c Reactance element 7 Band pass filter 8 Amplifier 9 Ranging part

Claims (9)

A transmission system that radiates a wave packet pulse that is a rectangular wave or a pseudo-rectangular wave modulated by a carrier wave, and receives the wave packet pulse from the target that is radiated from the transmission system and reflected or scattered by the target. In an equivalent time sample radar device having a receiving system for receiving as a received pulse with an antenna,
The receiving system, by performing said receiving pulses, the convolution integral is based on the sample pulse is a square wave or pseudo-rectangular wave having a pulse width that matches the one cycle time of the carrier wave of said wave packets pulse, the received pulse Equivalent time sampling radar apparatus characterized by performing equivalent time sampling for .   2. The equivalent time sample radar device according to claim 1, wherein a frequency of a fundamental wave of the sample pulse is ½ of a frequency of a carrier wave of the reception pulse. The receiving system is
A sample pulse generator for generating the sample pulse having a pulse width that matches one cycle time of the carrier wave of the received pulse;
A sample hold circuit that holds the voltage of the received pulse according to the timing of the sample pulse and outputs a sample signal;
Pulse shaping that is provided between the sample pulse generator and the sample hold circuit and shapes the sample pulse so that the rise and fall of the waveform of the sample pulse generated by the sample pulse generator is steep. The equivalent time sample radar device according to claim 1, further comprising:   4. The equivalent time sample radar device according to claim 3, wherein the reception system further includes a band-pass filter provided between the reception antenna and the sample and hold circuit.   5. The equivalent time sample radar device according to claim 3, wherein the reception system further includes an amplifier that amplifies the sample signal among the sample signals output from the sample hold circuit. 6. The sample and hold circuit includes :
An input terminal to which an input signal to be sampled is input;
An output terminal for outputting an output signal after sampling processing;
A pulse end to which a sample pulse defining a sampling time is supplied;
A first impedance element having one end connected to the pulse end and the other end connected to the output end;
One end is connected to the output end, the other end is connected to the input end, and a capacitor for holding the voltage of the input signal,
A second impedance that is connected to the input end and grounded at the other end and has a high impedance when viewed from the input end, and a low impedance when viewed from the capacitor or the frequency of the output signal. 6. The equivalent time sample radar device according to claim 3 , further comprising an element. The first impedance element has a high impedance when the sample pulse is at a first level, and causes the capacitor to hold an input signal, and the sample pulse has a second level different from the first level. The equivalent time sample radar device according to claim 6, wherein the equivalent time sample radar device is a semiconductor switch element having a low impedance. 8. The coil according to claim 6, wherein the second impedance element is a coil having a high impedance with respect to a frequency of the input signal and a low impedance with respect to a frequency other than the frequency of the input signal. Equivalent time sample radar device described in 1. The sample and hold circuit includes:
Provided between the input terminal and the capacitor, further comprising a low-pass filter;
9. The equivalent time sample radar device according to claim 8, wherein the second impedance element is the coil of the low-pass filter.

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