JPH0519045A - Fm radar - Google Patents

Abstract

PURPOSE:To enable a detection distance to be increased without increasing a transmission power by switching an amount of frequency change per unit time of a transmission wave in multiple stages and then obtaining a distance to a target based on a frequency sweep speed of the transmission wave and a beat frequency. CONSTITUTION:An FM signal generation circuit 2 generates a signal with a specified frequency based on frequency specification voltage signals 3a and 3b which are supplied to a frequency control terminal 2a and then supplies it to an input terminal 4a of a power distributor 4 from an output terminal 2b. A sweep speed switching means 3 switches an amount of frequency change per unit time of a transmission wave in multiple stages and then generates the triangular frequency specification voltage signals 3a and 3b with different cycles alternately. A distance-detection circuit 8 is provided with an amplification circuit which amplifies a beat signal 7c and a beat signal detection circuit which detects a frequency or a cycle of beat signal and then obtains a distance to a target based on the frequency sweep speed of the transmission wave and a beat frequency. A frequency band of a reception system can be maintained to be narrow by allowing a sweep cycle of the transmission wave to be different.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM radar capable of expanding a detection distance with a predetermined transmission power.

[0002]

2. Description of the Related Art An FM radar that emits a transmission wave whose frequency changes linearly with time and measures a target distance from the difference between the instantaneous frequencies of the transmission wave and the reception wave is relatively short distance (for example, several hundred meters). ), And is used for measuring the distance between automobiles and the distance to an obstacle (for example, JP-A-64-86064 and JP-B-63-4371).
No. 5, etc.). It is known that the radar detection distance is represented by the radar equation shown in Formula 1.

[0003]

[Equation 1]

[0004]

When realizing such an FM radar, the following three points are restricted by the Radio Law,
This is the most important matter. (1) Reduction of transmission power (2) Narrowing of frequency band (3) Stabilization of transmission frequency Among these, reduction of transmission power is an important factor that determines the detection distance and performance as a radar. Therefore, it is desirable to be able to detect a predetermined distance range with a small transmission power.

FIG. 4 is an explanatory diagram showing the relationship among the transmitted wave, the received wave and the beat frequency. Transmit wave TS (center frequency f
0, frequency deviation ΔF, lower limit frequency f1 to upper limit frequency f
The frequency fB of the beat signal between the reception wave RS and the sweep period T of the triangular wave-like frequency modulation in which the frequency monotonically increases to 2 and then monotonically decreases to the lower limit frequency f1 is the transmission wave TS.
And the received wave RS increase in proportion to the time difference ΔT (distance to the target).

Therefore, in order to increase the detection distance, it is necessary to widen the frequency band of the reception system such as the amplification system of the beat signal and the detection system. However, if the band of the receiving system is widened, the thermal noise of the receiving system increases accordingly, and the signal-to-noise ratio (S / N) deteriorates. Therefore, unless the transmission power is increased, the object cannot be detected and the distance cannot be measured.

The present invention has been made to solve the above problems, and an object thereof is to provide an FM radar capable of increasing the detection distance without increasing the transmission power.

[0008]

In order to solve the above problems, an FM radar according to the present invention comprises a sweep speed switching means for switching the frequency change amount of a transmission wave per unit time in multiple stages, and a frequency sweep speed of the transmission wave. And distance calculating means for calculating the distance to the object based on the beat frequency.

[0009]

With the sweep cycle when the first detection distance range is set as the detection target, the sweep cycle when the detection range is N times that of the first detection distance range is set to 1 / N, whereby each detection distance range is set. The range of beat frequencies at is constant. In other words, when detecting a distant object, the arrival time of the reflected wave becomes long, so that a predetermined beat frequency can be obtained even if the frequency change amount of the transmitted wave per unit time is reduced.
Therefore, the frequency band of the receiving system can be kept narrow by varying the sweep cycle of the transmission wave. Since thermal noise in the receiving system can be reduced by narrowing the band, a farther target can be detected and the distance can be obtained without increasing the transmission power while satisfying a predetermined signal-to-noise ratio (S / N). be able to.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of an FM radar according to the present invention. The FM radar 1 includes an FM signal generation circuit 2, a sweep speed switching unit 3, and a power distributor 4.
A circulator 5, an antenna 6 for both transmission and reception,
It is composed of a mixing circuit 7 and a distance detecting circuit 8.

The FM signal generation circuit 2 has a frequency control terminal 2
A signal having a specified frequency is generated based on the frequency specifying voltage signals 3a and 3b supplied to a, and is supplied from the output terminal 2b to the input terminal 4a of the power distributor 4. The FM signal generation circuit 2 is a voltage-controlled oscillator configured by combining an FET and a variable capacitance diode to generate a quasi-millimeter wave band signal, which is frequency-multiplied and power-amplified to generate a millimeter wave band signal. To generate. Alternatively, a voltage-controlled oscillation circuit using a Gunn diode may be used to directly generate a millimeter-wave band signal for power amplification.

As shown in FIG. 2A, the sweep speed switching means 3 is configured to alternately generate triangular wave-shaped frequency designation voltage signals 3a and 3b having different periods. The cycle of the frequency specifying voltage signal 3a for short distances is set to twice the cycle T1 of the frequency specifying voltage signal 3a for long distances. This sweep speed switching means 3 has information 3c (see FIG. 2b) relating to the currently output sweep cycle, and information 3d (see FIG. 2c) indicating whether the frequency change is in the increasing mode or the decreasing mode. The distance detection circuit 8
It is configured to supply to.

The millimeter-wave band FM signal 2b output from the FM signal generation circuit 2 is distributed by the power distribution circuit 4 composed of a directional coupler or the like, and one signal 4a is passed through the circulator 5 to the antenna 6 Emitted from. Other signal 4
b is supplied to one input terminal 7 a of the mixing circuit 7.

The received wave received by the antenna 6 is supplied to the other input terminal 7b of the mixing circuit 7 via the circulator 5. The mixing circuit 7 mixes the signals supplied to the input terminals 7a and 7b and outputs the beat signal 7c.

The distance detection circuit 8 is an amplification circuit for amplifying the beat signal 7c, a beat frequency detection circuit for detecting the frequency or cycle of the beat signal, and detection distance information based on the detected beat frequency and the current sweep speed. An arithmetic circuit for outputting 8a is provided.

Table 1 shows the relationship between the sweep speed and the beat frequency.
It shows the case where the distance to the object is 80 meters and 160 meters. Frequency sweep width is 400
MHz.

[0017]

[Table 1]

If the distance to the object is constant, the frequency of the beat signal becomes higher as the sweep speed becomes faster, and it is necessary to widen the frequency band of the beat signal amplifier. Even if the sweep speed is constant, the frequency of the beat signal increases as the distance to the object increases.

Therefore, in this embodiment, the maximum detection distance in the short-distance detection mode is 80 meters, the maximum detection distance in the long-distance detection mode is 160 meters, and the sweep speeds are 200 μS and 400 μS, respectively, and the maximum beat frequency of the beat signal is set. Is set to 2.132 MHz. Then, the frequency band of the receiving system such as the beat signal amplifier is set to 2.132.
Bandwidth is narrowed to MHz.

As described above, since the sweep speed of the FM-modulated transmission wave is slowed according to the maximum detection distance, the maximum beat frequency of the beat signal can be kept within a predetermined range. Therefore, by narrowing the frequency band of the receiving system, it is possible to reduce the thermal noise of the receiving system and increase the maximum detection distance at a predetermined transmission power.

In this embodiment, the modulation deviation width (for example, 400 MHz from 59.8 GHz to 60.2 GHz) of the FM-modulated transmission signal is made constant and the sweep cycle is made different, but the sweep cycle is constant. The modulation deviation width may be switched between 200 MHz and 400 MHz, for example. Further, the number of switching stages may be three or more.

In this embodiment, the configuration has been described in which the sweep speed for short distance and the sweep speed for long distance are alternately switched. However, it is determined that the distance to the object in the distance detection circuit 8 is shorter than a preset distance. Means for supplying the determination output to the sweep speed switching means 3, and the sweep speed switching means 3 continuously sweeps at the short range sweep speed while the object is in the short range based on the determination output. However, when there is no object at a short distance, the sweep may be continued at the sweep speed for long distance. Further, the determination of the switching of the sweep speed may be performed in the sweep speed switching means 3 by supplying the detected distance information 8a to the sweep speed switching means 3.

FIG. 3 is a block diagram of another FM radar according to the present invention. The distance detection circuit 18 of the FM radar 11 includes a low pass filter (LPF) 21a having a cutoff frequency of about 2.2 MHz and a frequency band of about 2.2 MH.
Reception system 21 for short-range detection, which includes an amplifier 21b for z
And a band pass filter (BPF) 22a having a low cutoff frequency of about 1 MHz and a high cutoff frequency of about 2.2 MHz,
A long-distance receiving system 22 including an amplifier 22b having a frequency band of about 1 MHz to 2.2 MHz, and sweep speed information 13c output from the sweep speed switching means 13.
Amplified outputs 21 of the receiving systems 21 and 22 corresponding to
The detection distance information 18a is obtained by calculating the distance to the object based on the selection circuit 23 that selects C and 22c, the frequency or the cycle of the selected output signal 23a, and the information 13c related to the sweep speed. And an arithmetic processing unit 24 for outputting.

Since the measurable distance in the short range detection mode does not have to be measured in the long range detection mode, the frequency band of the long range reception system 22 has a beat frequency in a long range (for example, a detection range of 80 to 160 meters). ) Is set only in the range, and the frequency band is narrower than the short-distance receiving system. With this configuration, the receiving system 2
It is possible to reduce the thermal noise of No. 2 and to secure the signal-to-noise ratio (S / N) at the time of long distance detection in which the signal level of the received wave becomes smaller.

In each of the embodiments, the transmitting / receiving antenna 6 is also used.
Although the configuration using the above is shown, the transmission antenna and the reception antenna are separately provided, and the transmission signal and the reception signal extracted by the power distributor 4 are heterodyne-detected by the mixing circuit 7 to extract the beat signal. Good.

[0026]

As described above, the FM according to the present invention
Since the radar is configured to switch the frequency change amount of the transmission wave per unit time according to the maximum detection distance, the beat frequency in each detection distance range can be set within a predetermined range. Therefore, it is possible to narrow the frequency band of the receiving system that performs amplification and processing of the beat signal, and the thermal noise of the receiving system can be reduced by narrowing the band. With the noise ratio (S / N) being satisfied, a farther object can be detected and its distance can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an FM radar according to the present invention.

FIG. 2 is a time chart of information relating to a frequency designation voltage signal and a sweep cycle.

FIG. 3 is a block diagram of another FM radar according to the present invention.

FIG. 4 is an explanatory diagram showing a relationship among a transmitted wave, a received wave, and a beat frequency.

[Explanation of symbols]

1, 11 ... FM radar, 2 ... FM signal generation circuit, 3 ...
Sweep speed switching means, 4 ... Power divider, 5 ... Circulator, 6 ... Transmitting / receiving antenna, 7 ... Mixing circuit, 8,
18 ... Distance detection circuit.

Claims (1)

Claim: What is claimed is: 1. An object which emits a transmission wave whose frequency changes linearly with time, and which is based on a beat signal generated between the reception wave and the transmission wave reflected by the object. In an FM radar that detects the distance to, the sweep speed switching means that switches the amount of change in the frequency per unit time in multiple stages, and the distance to the object based on the frequency sweep speed of the transmitted wave and the beat frequency. An FM radar, comprising: a distance calculating unit for obtaining the distance.