Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an anti-collision vehicle radar
system, adapted to control the operation of a vehicle, so as to
avoid collisions with other vehicles and with obstacles of all
kinds.
The radar system is applicable to vehicles generally, in-
! cludin~ passenger automobiles, trucks, buses, rapid transit trains,
and all other types of railroad trains, for example.
~ Many such anti~collision vehicle radar systems have been
; proposed in the prior art. Typically, such an anti-collision
radar system includes a radar transmitter, a transmitting antenna
mounted on the vehicle for transmitting a radar beam in a forward
' ~t direction from the vehicle, and a radar receiver for receiving the
reflected radar beam, after it has been reflected by another vehicle
or any other obstacle. The radar system may include means for
measuring the range or distance be-tween the vehicle and the ob-
stacle, and also the rate or velocity with which the vehicle is
approaching the obstacle. The radar system may include means for
automatically actuating the brakes of the vehicle, if the range
and velocity information indicates that it is necessary to stop
or slow down the vehicle to avoid a collision with the obstacle.
Prior anti-collision vehicle radar systems have been af1icted
with the problem of interference from radar beams transmitted by
- similar radar systems on other vehicles. An anti-collision radar
system is not of mu~h value unless radar units can be installed on
all vehicles, without causing interference problems between the
radar units on approaching vehicles. With prior radar systems, the
radar units on approaching vehicles have severely interfered with
each other, in that each radar receiver has been blinded or over-
loaded by the strong radar beam from the approaching vehicle, to
such an extent that each radar receiver has been rendered incapable
of effectively receiving the weaker reflected beam from its own
transmitter.
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The principal object of the prevent invention is to provide
a new and improved anti-collision vehicle radar system which is -
capable of discriminating in favor oE the reElected radar beam,
while discriminating a~ainst any radar ~eam from a similar radar
system on another vehicle, so that the radar system can effectively
receive and analyze the reflected beam, without being blinded by
any radar beam from another vehicle.
In accordance with the present invention, this objective
is achieved by providing radar transmitting means for transmitting
a radar beam having circular polarization with a particular direct-
tion of rotation of the polarization, radar receiving means for
receiving the beam after reflection thereof and including means
for discriminating in favor of received signals having circular
polarization with such particular direction of rotation, while
discriminating against received signals having circular polarization
with the opposite direction of rotation of the polarization, and
utilization means connected to the receiving means for utilizing
received radar signals to control the operation of the vehicle.
In this way, the receivin~ means is effective to discriminate in
~avor of the reflected radar beam while discriminating against any
interfering radar beam from another vehicle radar system. The
transmitted radar beam, with its circular polarization, is re-
flected from obstaclles without any change in the direction of -~
rotation of the polarization. However, the circularly polarized
beam from an approaching vehicle is received with the opposite
direction of rotation of the polarization, due to the fact that
the orientation of the approaching vehicle is reversed relative
to the orientation of the base vehicle.
To produce the circularly polarized radar beamt the radar
transmitter may employ transmitting antenna means having a coiled
antenna element. The receiving antenna means may employ an antenna
element which is coiled in the opposi-te direction, to discriminate
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against any interfering radar beam. The transmitting and receiving
antenna elements are preferably helical in shape, with opposite
coiling directions. The helical antenna elements have the additional
advantage of being highly directional, so as to produce a narrow
beam width.
Further objects, advantages and features oE the present
invention will appear from the following description, taken ~Yith
the accompanying drawings, in which:
Fig. 1 is a diagrammatic plan view showing two approaching
vehicles equipp~d with anti-collision radar systems to be des-
cribed as illustrative embodiments of the present invention.
Fig. 2 is a diagrammatic sectional view showing a helical
radar antenna which may be employed in the radar system.
Fig. 3 is a more detailed sectional view showing a similar
helical antenna, but with an opposite coiling direction.
Fig. 4 is a front view of the helical antenna of Fig. 3.
Fig. 1 illustrates two identical vehicles 10 having iden-
tical radar systems 12, to be described as illustrative ernbodiments
of the present invention. Each radar system 12 comprises radar
transmitting means including a helical transmitting antenna 14
connected to a radar transmitter 15. Each radar system 12 also
comprises receiving means including a helical receiving antenna 16
connected to a radar receiver 18, the outpu-t of which is connected
to a signal processo:c 20, adapted to operate utilization devices 22
for controlling the operation of the vehicle. The transmit-ter 15,
receiver 18, signal processor 20 and utilization devices 22 may
employ the technology o~ the prior art, or any other suitable
technology.
As shown, the helical transmitting and receiving antennas 14
and 16 comprise helical coils 24T and 24R, which are mounted in
front of metal plates 26 sarving as reflectors. The transmitting
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antenna 14 o each radar system 12 radiates a circularly polarized
radar beam in which the polarization rotates in a particular direc-
tion, which may be e~ither clockwise or counterclockwise, but is
the same for all of the radar systems on all vehicles. This radar
; beam is reflected by any obstruction and is returned with the same
; absolute direction of rotation oE the polariza-~ion. The receiving
antenna 16 is constructed so as to discriminate in favor of this
direction oE rotation.
If two vehicles are approaching each other while travelling
in opposite directions, as illustrated in Fig. 1, each radar system
will receive any interfering radar beam from the system on the other
vehicle, in addition to its own reflected beam. The interfering
',J beam has a circular polarization which is rotating in the opposite
direction, because the interfering beam is being viewed from the
receiving end of the beam rather than from the transmitting end.
`t Thus, if each radar system is transmitting a radar beam with clock-
wise polarization, the interfering beam ~ro~ another vehicle headed
or oriented in the opposite direction is received with a coun-ter-
clockwise polarization, while its own reflected beam is received
~-0 with a clockwise polarization. The receiving antenna 16 o-f each
; radar system is then constructed so as to discriminate against the
counterclockwise polarization of the interfering beam, while dis- -
criminating in favor of the clockwise polarization of ~he reflected -
beam. In this way, the interfering beam can be rejected or attenu-
ated by as much as 40 D.B., relative to -the reflected beam, so that
each radar system will be able to distinguish between the reflected
beam and the interfering beam. Thus, each radar system is able to
receive, analyze and measure its own re1ected beam, without being
blinded, overloaded or confused by an interfering beam.
To achieve the desired discrimination, the helical receiving
antenna element 24R should be coiled in the opposite direction,
relative to the coiling direction of the transmitting antenna
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element 241'. The opposite coiling directions are illustrated in
Fig. 1. Except for the opposite coiling directions, the trans-
mittin~ and receiving an-tennas 14 and 16 may be basically the same.
Additional details of the transmitting and receiving antennas
1~ and 16 are shown in Figs. 2, 3 and ~. Fig. 2 is diagramma~ic,
while Fig. 3 is more detailed. It may be considered that Fig. 2
illustrates the receiving antenna 16, while Figs. 3 and 4 illus-trate
~he transmitting antenna 14. It wil] be noted that the opposite
coiling directions are employed for the helical receiving antenna
element 24R and the helical transmitting antenna element 24T. In
each case, the axis of the coil 24R and 24T coincides with the desired
direction of propagation. The conductive reflector pla-te 26 is per-
pendicular to the axis oE the helical coil 24T or 24R.
In each case, the antenna coil 24T or R is fed by forming o~e
end of the coil into an axial lead 30 which may be coupled to a co-
axial line or a wave guide. As shown in Fig. 3, the lead 30 extends
axially through a cylindrical bore 32 in a cylindrical conductor 34,
into a wave guide 36. Within the wave guide 36, the end of the lead
30 serves as a probe 38, terminating in a ball 40 which is for the
purpose of broad band matching. The wa~e guide 36 may be employed
to supply energy to or from the antenna 14 or 16. The illustrated
wave guide 36 has a tuning stub 42 in which a conductive tuning slug ~ -
44 is slidable. Any known or suitable wave guide or other feed
technology may be employed The antenna element 24T or R may be
tuned by adjusting the length or position of the lead 3~.
The helical transmitting and receiving antennas 1~ and 16
have the additional advantage of being highly directional, so as to
provide a narrow beam width. In this way, interference is reduced
and the strength o~ the re~lected beam is increased~
The helical transmittiny antenna 14 radiates electromagnetic
radio waves having circular polarization. Other types of antennas
may be employed to radiate waves having circular polarization. For
example, other types of coiled antenna elements may be employed,
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such as spiral coils~
In a circularly polarized wave, -the transverse polarization
of the wave rotates. In the case o~ the helical transmitting an-
tenna 14, the direction of rotation depends upon the coiling direc-
tion of the helical coil. A circularly polari~ed wave may be re-
garded as comprising two wave components which are 90 out of phase
electrically and are polarized alony transverse planes which are
90 apart, such as horizontal and vertical planes. The two wave
components combine to form a wave which is circular or rotary.
10 The rotation of the polarization may be in either direction about
the axis of propagation of the wave.
The radar system of the present invention may be operated
a-t various radio frequencies, but it is particularly advantageous
to operate the radar system at extreme ultra-high frequencies,
such as the so called X band at about 10 gigahertz. In this band,
a hiyh degree of directionality can be achieved with small antennas.
Thus, the helical transmitting and receiving antennas 14 and 16 will
achieve an e~tremely narrow beam width.
Any known or suitable radar technology may be employed to
analyze and measure the reflected radar signals. Thus, technology
is available to measure the range or distance be-tween the vehicle
and the obstruction, and also the relative speed or velocity between
the vehicle and the obstacle. The radar system may be programmed
to operate the brakes of the vehicle automatlcally, if the range
and velocity information indicate that there is danger of a colli-
sion between the vehicle and the obstacle. Other controls of the
vehicles can also be operated, if desired.
With the radar system of the present invention, every auto-
mobile and every other automo~ive vehicle can be equipped with a
radar sek to prevent any vehicle from collidiny with another vehicle
or any other obstacle. The radar sets on approaching vehicles will
not interfere with one another, because each radar set is able to
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discriminate in favor of its own reflected beam, while discriminat-
ing against the beam from an oncoming vehicle. This discrimination
results from the circular polariza-tion oE`the transmit-ted radar
beams, plus the ability of the receiving antennas to discriminate
in favor of circular polarization in one direction of rotation,
while discrimina-ting against circular polarization in the opposite
direction o rotation.
