Communications: directive radio wave systems and devices (e.g. – Return signal controls external device – Radar mounted on and controls land vehicle
Reexamination Certificate
2000-08-10
2002-05-07
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Return signal controls external device
Radar mounted on and controls land vehicle
C342S089000, C342S094000, C342S104000, C342S109000, C342S118000, C342S128000, C342S134000, C342S165000, C342S173000, C342S195000
Reexamination Certificate
active
06384768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to Doppler radar, and more particularly to an FM pulse Doppler radar apparatus, such as a radar apparatus mounted on a vehicle, for determining the distance to an object.
2. Description of the Related Art
As for this type of radar apparatus, an FM pulse Doppler radar illustrated in
FIG. 10
is known in the art. Referring to
FIG. 10
, the FM pulse Doppler radar apparatus includes a modulation-voltage generator
1
, a voltage-controlled oscillator (triangular wave generator)
2
for generating electromagnetic waves having transmission frequency f
tx
of, for example, 76 to 77 GHz, a transmit-receive switch
3
for switching the output feed of the electromagnetic waves generated by the voltage-controlled oscillator
2
between a transmitting amplifier
4
and a receiving mixer
9
, the transmitting amplifier
4
for amplifying the power of the electromagnetic waves fed by the transmit-receive switch
3
, and a transmitting antenna
5
for radiating the electromagnetic waves amplified by the transmitting amplifier
4
.
Further in
FIG. 10
, an object
6
is a target to be detected by the radar. The apparatus also includes a receiving antenna
7
for receiving the electromagnetic waves radiated to and reflected from the object
6
, and a receiving amplifier
8
for amplifying the received electromagnetic waves.
The apparatus further includes the mixer
9
for outputting beat signals corresponding to the distance and relative velocity of the object
6
by mixing transmission electromagnetic waves switched by the transmit-receive switch
3
and electromagnetic waves reflected back from the object
6
, a low-pass filter
10
of which the cut-off frequency is the inverse of the transmission pulse time width, an AGC amplifier
11
capable of controlling the gain according to the received power of the reflected waves, an A/D converter
12
for converting the beat signals into digital signals, and a distance calculator
13
for calculating the distance and relative velocity of the object
6
based on the A/D values.
An electromagnetic wave transmitting operation of a typical known radar apparatus having the above-described structure will now be described.
First, the voltage-controlled oscillator
2
outputs electromagnetic waves (triangular wave signals) modulated, for example, as in
FIG. 2
, corresponding to the voltage signals from the modulation-voltage generator
1
. The electromagnetic waves output from the voltage-controlled oscillator
2
are fed to the transmitting amplifier
4
by the transmit-receive switch
3
and are amplified therein. The electromagnetic waves amplified by the transmitting amplifier
4
are radiated from the transmitting antenna
5
.
Next, an electromagnetic wave receiving-operation will be described. The transmit-receive switch
3
is switched to the receiving side to connect the voltage-controlled oscillator
2
and the mixer
9
when a pulse time width T
g
, for example, of 33.3 ns (=1/30 MHz, equivalent to a distance of 5 m) has elapsed from the time electromagnetic wave transmission was initiated. The electromagnetic waves sent from the transmitting antenna
5
form pulse waves, each pulse having a duration of 33.3 ns. The pulse waves are reflected ago by the object
6
at a distance R, and input to the receiving antenna
7
after a delay time &Dgr;t depending on the distance R relative to the transmitted electromagnetic waves.
When the object
6
has a relative velocity, the frequency of the received electromagnetic waves is Doppler-shifted relative to the frequency of the transmission electromagnetic waves, and they are input to the receiving antenna
7
. The electromagnetic waves input to the receiving antenna
7
are amplified by the receiving amplifier
8
and mixed with the transmission electromagnetic waves from the voltage-controlled oscillator
2
by the mixer
9
to output beat signals shown in FIG.
3
. The beat signals thus acquired pass through the low-pass filter
10
, of which the cut-off frequency is, for example, 30 MHz, are amplified by the AGC amplifier
11
, are input in the A/D converter
12
, and are converted to digital signals.
Next, a method for calculating the distance and relative velocity of the object
6
by the distance calculator
13
based on the output data from the A/D converter
12
is explained.
For the purpose of understanding, it is assumed that the voltage-controlled oscillator
2
does not perform FM modulation and the transmission frequency f
tx
is fixed to 76.5 GHz. In order to obtain a velocity resolution of 1 km/h, a Doppler frequency resolution &Dgr;f is:
Δ
f
=
2
Δ
v
λ
=
2
×
0.2777
m
/
s
0.003921
m
=
141.64
(
Hz
)
=
1
7.05977
(
ms
)
=
1
Tm
(
1
)
and a calculation time T
m
of approximately 7.06 ms is required. If, for example, the maximum detection range is set to 150 m, then the transmission wave output cycle is 33.3 ns×(150/5)=1 &mgr;s. In order to obtain the velocity resolution of 1 km/h, the above-described device acquires, at each range gate, beat signals for the transmitted waves output 7060 times, as in
FIG. 4
, and performs, for each of the range gates, a fast-Fourier-transform of all the data. Then the beat frequency at a particular range gate is output as shown in FIG.
5
.
The distance R
g
and the relative velocity V may be calculated using equations (2) and (3) below:
Rg
=
tg
×
n
×
C
2
(
2
)
V
=
fb1
×
C
2
×
f0
(
3
)
where t
g
is a range gate time width (pulse time width), n is a range gate number, c is the speed of light, f
b1
is a Doppler frequency (=beat frequency), and f
0
is the transmission frequency (76.5 GHz).
Now, consider that the above-described transmission electromagnetic waves are modulated as in FIG.
2
. Suppose that during the above-described calculation time T
m
of approximately 7.06 ms, the transmission frequency is increasing steadily from 76.425 to 76.575 GHz, the bandwidth B being 150 MHz. The time t required for the electromagnetic waves to be transmitted from the transmitting antenna
5
, reflected from the object
6
and input to the receiving antenna
7
may be found by the following equation (4):
t
=
distance
×
2
C
(
4
)
As the transmission frequency is increasing steadily during the time t, the beat frequency f
bu
is found by summing the Doppler frequency f
b1
due to the relative velocity and f
b2
which represents the difference between transmission frequency and the received frequency corresponding to the distance, as follows:
fbu=fb
2
+
fb
1
(5)
Likewise, suppose that the transmission frequency is steadily decreasing from 76.575 GHz to 76.425 GHz, the bandwidth B being 150 MHz, during the next calculation time T
m
of approximately 7.06 ms. As the transmission frequency is decreasing during time t required for the electromagnetic waves to be output from the transmitting antenna
5
, reflected from the object
6
and input to the receiving antenna
7
, the beat frequency f
b1
may be obtained by summing a Doppler frequency f
b1′
due to the relative velocity and f
b2′
which represents the difference between the transmission frequency and the received frequency corresponding to the distance. The interval of increasing/decreasing the frequency, the distance, and the relative velocity between the radar and the object may be the same as in the foregoing case of increasing the frequency. Because the bandwidth remains constant and the increase/decrease rate is equal, f
b1
=f
b1′
and f
b2′
=−f
b2
. The beat frequency f
bd
may be obtained by equation (6) below:
fbd=fb
2
′+
fb
1
′=−
fb
2
+
fb
1
(6)
As the beat frequency f
bu
can be obtained by increasing the transmission frequency and the beat frequency f
bd
can be obtained by decreasing the transmission freque
Gregory Bernarr E.
Mitsubishi Denki & Kabushiki Kaisha
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