Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2002-07-11
2003-07-22
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S128000, C342S199000
Reexamination Certificate
active
06597308
ABSTRACT:
The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-211314 filed on Jul. 11, which is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radar apparatus using frequency modulation (FM) such as an FM-CW system and in particular to detection and correction of the frequency modulation characteristic thereof.
2. Description of the Related Art
Hitherto, an FM-CW system radar
1
having a basic configuration as shown in
FIG. 16
has been mainly installed in an automobile for use to give a collision alarm, prevent or lighten a collision, perform vehicle-to-vehicle control of auto cruise control, drive a car, etc.
FIG. 16
(
a
) shows a schematic electric configuration and
FIG. 16
(
b
) shows a modulation signal waveform. Related arts to the FM-CW system radar are disclosed in JP-A-5-40169, JP-A-7-55942, JP-A-8-327728, etc., for example. JP-A-5-40169 discloses an art for using second frequency modulation to improve the reception S/N ratio.
In the basic configuration of the FM-CW system radar
1
, a radio wave is transmitted from a transmission antenna
2
and the reflected radio wave from a target, etc., is received at a reception antenna
3
, as shown in
FIG. 16
(
a
). A high-frequency signal of a millimeter waveband generated from a VCO (voltage-controlled oscillator)
4
is given to the transmission antenna
2
. A part of the high-frequency signal for exciting the transmission antenna
2
from the VCO
4
branches from a coupler
5
and is mixed with a reception signal from the reception antenna
3
by a mixer
6
. An output signal from the mixer
6
is selected through a BPF (band-pass filter)
7
and is amplified by an amplifier
8
. The high-frequency signal generated from the VCO
4
is subjected to frequency modulation in accordance with the voltage level of a modulation signal given by a modulation signal generation circuit
9
.
For example, in the FM-CW system radar
1
of a millimeter waveband, a modulation signal shaped like a triangular wave of about several hundred Hz as shown in
FIG. 16
(
b
) is used to generate an FM wave with the maximum frequency shift amount being several ten to several hundred MHz. As the modulation signal, a saw tooth wave (chirp wave) maybe used in some cases. If the frequency modulation characteristic of the VCO
4
has good linearity relative to change in the voltage level of the modulation signal, the frequency of the high-frequency signal generated from the VCO
4
also changes linearly corresponding to
FIG. 16
(
b
). The frequency of the reflected radio wave received at the reception antenna
3
is delayed from the frequency of the high-frequency signal given to the transmission antenna
2
as much as the time taken for the radio wave to go and back at the distance to the target. If the high-frequency signal whose frequency changes like a triangular wave corresponding to
FIG. 16
(
b
) is generated from the VCO
4
and the distance to the target is constant, the signal output from the mixer
6
contains a beat signal component of a constant frequency corresponding to the time taken for the radio wave to go and back at the distance. The beat signal component is selected through the BPF
7
and is amplified by the amplifier
8
and then can be input to a signal processing circuit
10
for calculating the distance to the target. When the distance to the target changes, the effect of Doppler shift appears in the frequency of the beat signal and the relative speed can also be calculated by the signal processing circuit
10
. Letting the frequency of the beat signal be fb, the frequency depending on the distance be fx, and the frequency depending on the relative speed be fd,
fb=fx±fd.
With the FM-CW system radar
1
, the frequency modulation characteristic in the VCO
4
has an importance effect on the measurement accuracy. JP-A-7-55942 discloses an art for previously measuring the frequency modulation characteristic of a voltage-controlled oscillator for generating a high-frequency signal of an FM-CW radar and making a correction with an inverse function of the measured characteristic for improving linearity. JP-A-8-327728 discloses an art for correcting a modulation signal so that the frequency of a high-frequency signal generated in an FM-CW radar apparatus changes like a triangular wave. JP-A-6-34756 discloses an art wherein the linearity of a voltage-controlled oscillator for generating a high-frequency signal as a source of a transmission radio wave in a radar transponder for transmitting a frequency-modulated radio wave and responding upon reception of a radio wave from a radar is corrected with data previously stored in memory. However, the related arts do not give any direct description as to how the frequency modulation characteristic is measured.
FIG. 17
shows a schematic configuration for measuring the frequency modulation characteristic and sensing whether or not linearity is maintained in the FM-CW system radar
1
in the related art shown in
FIG. 16
(
a
). Another signal source
11
is provided, the high-frequency signal from the VCO
4
is branched by a coupler
12
and is mixed by a mixer
13
for down conversion, and the difference from the frequency of the signal source
11
is counted by a counter
14
. In addition to such down conversion, a method of counting the frequency of the high-frequency signal from the VCO
4
is also available.
The FM-CW system radar
1
, etc., installed in a vehicle is used in a hostile environment concerning vibration, temperature, etc. Thus, if the linearity of the frequency modulation characteristic is good at the initial stage, there is a possibility of degradation while the radar is used. If the down converter configuration as shown in
FIG. 17
is adopted to install a configuration for detecting the linearity of the frequency modulation characteristic in the FM-CW system radar
1
itself, as the signal source
11
, the mixer
13
, and the like, expensive components for high frequencies of a millimeter waveband become necessary. To count the frequency of the high-frequency signal from the VCO
4
, the millimeter waveband cannot directly be counted and therefore a frequency divider needs to be used. However, the frequency divider operating in the millimeter waveband is expensive and as the frequency dividing ratio increases, the measurement accuracy is degraded.
That is, if an attempt is made to detect and correct the frequency modulation characteristic in the system in the related art as shown in
FIG. 17
, the following problems are involved:
(1) The higher the transmission frequency, the higher the costs of the components, such as a detector and a frequency divider.
(2) The higher the transmission frequency, the larger the frequency dividing ratio and the worse the measurement accuracy.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide a radar apparatus that can detect and correct the frequency modulation characteristic in a simple configuration at low costs.
According to the invention, there is provided a radar apparatus for performing frequency modulation of a high-frequency signal, transmitting the frequency-modulated signal, and receiving a reflected radio wave to detect a target, the radar apparatus including a high frequency generation section for generating the high-frequency signal, a modulation signal generation section for generating and giving a modulation signal to the high frequency generation section to modulate the high frequency signal, a mixing section for mixing the high-frequency signal and the reception signal of the reflected radio wave, and a signal processing section for controlling the modulation signal generation section so as to give a modulation signal for detection changing among a plurality of predetermined signal levels and retained for a predetermined time for each signal level to the high frequency generation section, detecting frequency of a differential signal between the high-
Andrea Brian K
Fujitsu Ten Limited
Oliff & Berridg,e PLC
Tarcza Thomas H.
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