JPH0353186A - Transmission frequency automatic adjusting circuit for fm-cw radar - Google Patents

Abstract

PURPOSE:To eliminate the variance of the transmission frequency due to the change of tempera ture or the like by switching the frequency modulation of a transmission signal at intervals of a prescribed time by a modulation signal for measurement, a modulation signal stopped with a minimum frequency, and a modulation signal for distance correction to automatically adjust the transmission frequency to minimum and maximum transmission frequencies. CONSTITUTION:The modulation signal supplied to a transmission circuit 2 is switched by a signal switch 11 and is corrected by a modulation voltage corrector 12. The signal of the circuit 2 is converted to a lower frequency by a frequency divider 13 and is inputted to a mixer 21 and a delay circuit 31 is parallel. A signal having a certain frequency is inputted to the mixer 21 in the period of a minimum transmission frequency determining modulation signal, a sampling and holding circuit 24 regards the output of a frequency discriminator 23 as the error voltage is accordance with signal switching of the switch 11, and the frequency modulated signal and the time delay signal are inputted to a mixer 32 in the period of a maximum transmission frequency determining modulation signal. A sampling and holding circuit 34 regards the output of a frequency discriminator 33 as the error voltage in accordance with signal switching of the switch 11. The maximum frequency is automatically controlled to the frequency determined by the delay time of the circuit 31, and the minimum transmission frequency is automatically controlled to the frequency determined by the reference quartz oscillator 22.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a circuit that automatically adjusts a transmission frequency in an FM-CW radar.

(Prior Art) Conventionally, to determine the distance of a target within a predetermined distance, a radar that performs sweep detection using a frequency-modulated continuous wave (so-called FM-CW) signal has been used.

Third [! 1 shows an example of the configuration of a radar system according to this method, that is, the FM-CW radar method.

A modulator 1 that generates a modulated signal F(t) having a constant slope is connected to a transmitting circuit 2 that outputs a transmitted signal frequency-modulated by the modulated signal F(t).

That is, as shown in FIG. 4(a), the modulator 1 generates a modulated signal F(t
) occurs. At this time, the slope has a certain amplitude. Further, in the transmission ε circuit 2, the transmission signal is frequency-modulated by this modulation signal F(t) and output. At this time, the frequency of the transmission {ε is shown in Fig. 4(b)
As shown in , the function f(
t).

Therefore, the frequency f(t) of the transmitted signal has a deviation bandwidth ΔF (eg 400M
Hz).

An antenna 3 that emits a transmission signal to a target object 4 and receives a reflected wave from the target object 4 is connected to the transmission circuit 2 via a mixer 5, and a part of the transmission signal 43 and a reception signal of the antenna 3 are connected to the transmission circuit 2. A receiving circuit 6 that amplifies the output of the mixer 5 is connected to the mixer 5 that performs mixing with the mixer 5 .

That is, the transmission signal is radiated as a radio wave by the antenna 3, and the reflected wave of this radio wave by the target object 4 is received by the antenna 3. The reflected wave received by the antenna 3 is used as a received signal to be sent to a mixer 5 as a part of the transmitted signal.
The mixer 5 generates a heating frequency fi(f b) corresponding to the frequency difference between the received signal and the transmitted signal.
For example, a beat signal having a frequency of 100 KHz) is output.

This beat frequency fb is a value proportional to the distance liID of the target object 4. That is, as shown in FIG. 4(b),
Since the transmitted signal and the received signal have a slope that is the ratio of the shift band intensity ΔF to the rise time T, the mixing of the transmitted signal and the received signal is related to the time difference τ between the transmitted signal and the received signal. The ratio of frequencies f, corresponds to the slope of the slope. Here, the time difference between the transmitted signal and the received signal is the reflection path length 2D with respect to the target object 4.
Since it is the radio wave transmission time related to On the other hand, as mentioned above, fb/τ=ΔF
/T, therefore, f,=(ΔF − 2 D)/(T − C)ocD
Therefore, the beat frequency fb is proportional to the distance D.

That is, the distance lllIID is found by measuring fb with ΔF and T known.

(Problem to be Solved by the Invention) However, according to the conventional FM-CW radar, a continuous modulation signal having a linear slope of constant amplitude is used to determine the shift bandwidth ΔF; If the oscillation constant of the circuit changes due to temperature characteristics or aging,
There was a problem that the transmission frequency fluctuated. The microwave circuit section is required to have wideband characteristics in order to cope with shifts in ΔF due to fluctuations in the transmission frequency, making design and adjustment difficult. In particular, this has been a major problem in the manufacture and adjustment of the multiplier in the microwave circuit section.

The present invention has been made to solve such problems, and is to prevent fluctuations in the transmission frequency.

(Means for Solving the Problems) In order to achieve the above object, the present invention modulates the frequency of the transmitted ε signal by using a measurement modulation signal, a modulation signal that pauses at the lowest frequency, and a distance calibration modulation signal (the highest frequency The transmission frequency is automatically adjusted to the lowest transmission frequency and the highest transmission frequency determined by another frequency (low frequency) that serves as a reference. Embodiments will be described in detail below with reference to the drawings.

(Embodiment) FIG. 1 shows the configuration of a radar system using an automatic transmission frequency adjustment circuit for an FM-CW radar according to an embodiment of the present invention. Components similar to those of the conventional example shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, 11 is a signal switch, l2 is a modulation voltage corrector, 13 is a frequency divider, 14 is a signal switch, 21 is a mixer, 22 is a reference crystal oscillator, 23 is a frequency discriminator, and 24 is a sample. 31 is a hold circuit, 3l is a delay circuit, 32 is a mixer, 33 is a frequency discriminator, and 34 is a sample and hold circuit.

In this embodiment, the modulator 1 includes a measurement modulation signal,
A modulation signal for determining the lowest transmission frequency and a modulation signal for determining the highest transmission frequency are added via the {g signal switch 11.

Further, in the transmission circuit 'Is2, the modulation M1 is connected to the modulation voltage corrector 1.
Connected via 2.

In other words, the modulated signal F(1) supplied to the transmission ε circuit 2
As shown in FIG. 2(a), a preset measurement modulation signal, a minimum transmission frequency determination modulation signal, and a maximum transmission frequency determination modulation signal are switched by a signal switching Wll and alternately The signal that appears is modulated voltage corrector 1
This is a signal corrected by 2. In the transmitting circuit 2, a transmitting signal frequency-modulated by this modulation A3 F(t) is outputted, as in the conventional example.

On the other hand, a part of the signal of the transmitting circuit 2, for example, the original oscillation signal of the transmitting circuit 2 (for example, 380 MHz band) is converted to a lower frequency by the frequency division M13, and then sent to the mixer 21 and It is connected in parallel to a delay circuit 31 and a mixer 32.

A signal of a constant frequency is input to the mixer 21 during the period (second time domain) of the modulation signal for determining the lowest transmission frequency. On the other hand, a reference crystal oscillator 22 is connected to this mixer 2l, and a difference frequency (fb) from the frequency of the reference crystal oscillator 22 is output.

A signal of this frequency is input to the frequency discriminator 23. The frequency discriminator 23 outputs a voltage proportional to the difference between the center frequency and the input frequency, and inputs it to the sample hold circuit 24. Then, the sample and hold circuit 24 holds the output of the frequency discriminator 23 as an error voltage as the fs signal switch 11 switches the signal.

The sample and hold circuit 24 includes a modulation voltage corrector 12.
is connected, and the lowest transmission frequency is automatically controlled by the error voltage to the frequency determined by the reference crystal oscillation &22.

On the other hand, the mixing M32 includes a signal frequency-modulated by a continuous modulation signal having a linear slope during the period (third time domain) of the modulation signal for determining the highest transmission frequency, and a signal that is frequency-modulated by a continuous modulation signal having a linear slope. A signal with a known time delay is input, and as a result, the difference frequency (fc) is output. A signal of this frequency is input to frequency discrimination W33. The frequency discriminator 33 outputs a voltage proportional to the difference between the center frequency and the input frequency, and inputs it to the sample and hold circuit 34. Then, the sample hold circuit 34 performs the waste wave number discrimination # as the signal switching device 11 switches the signal.
The output of 33 is held as an error voltage.

The sample and hold circuit 34 includes a modulation voltage corrector l.
2 are connected, and the highest transmission frequency is automatically controlled by the voltage to a frequency determined based on the delay time of the delay circuit 31.

In this way, the distance determination in the l-th time domain is performed based on the lowest frequency and the highest frequency determined in the second and third time domains.

(Effects of the Invention) As described above, according to the present invention, since the transmission frequency is automatically controlled, there is no fluctuation in the transmission frequency due to changes in the transmitting circuit, changes over time, etc., and the design of the microwave circuit section is improved.
Adjustment becomes easy. Further, since the shift band intensity ΔF is constant, the error in the distance HD measured as a function of the ΔF is also eliminated.

[Brief explanation of drawings]

FIG. 1 shows a servo slope FM- according to an embodiment of the present invention.
Configuration diagram of a radar system using the CW radar method, Part 2
The figures are operation diagrams of the radar system shown in Fig. 1, in which Fig. 2 (a) is a chart of a modulated signal, and Fig. 2 (b) is a diagram of the operation of the radar system shown in Fig. 1.
) is a chart showing the tying of the transmit {3 signal and the received signal, FIG. 3 is a conventional servo slope type FM-CW.
FIG. 4 is a configuration diagram of a radar system using a radar system, and is an operational diagram of the radar system shown in FIG.
FIG. 4(a) is a chart showing the modulation signal, FIG.
b) is a chart showing the timing of the transmission A3 and the received signal. DESCRIPTION OF SYMBOLS 1... Modulation block, 2... Transmission A ε circuit, 6... Receiving circuit, l1... A3 switch, 12... Modulation voltage corrector, 21... Mixer, 22 ...Reference crystal oscillator, 2
3... Frequency discriminator, 31... Delay circuit, 32...
- Mixer, 33... frequency discriminator.

Claims (1)

[Claims] A transmission signal frequency-modulated by a continuous modulation signal having a linear slope of constant amplitude is radiated as a radio wave, and a part of the transmission signal is mixed with a reception signal including a reflected wave from a target object to generate a frequency difference ( In the FM-CW radar that measures the distance from f_b) to a target, means for sequentially switching within one cycle of the transmission signal at predetermined time intervals;
means for detecting the frequency difference (f_b) and outputting a distance signal in a time domain, and means for stopping frequency modulation at the lowest frequency and detecting the frequency difference (f_r) between the lowest frequency and the reference frequency in a second time domain. ) and controlling the frequency difference (f_r) to a known frequency to determine the lowest transmission frequency; ), and determining a frequency deviation width by controlling the frequency difference (f_c) to a known frequency, and determining the highest frequency based on the determination of the lowest transmission frequency,
Automatic transmission frequency adjustment of the FM-CW radar, characterized in that it is configured to perform distance measurement in the first time domain based on the lowest transmission frequency and the highest transmission frequency determined in the third time domain. circuit.