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Патент USA US2403622

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Patented July 9, 1946
Clarence D. Tuska,l Philadelphia, Pa., assignor to
Radio Corporation of Americma corporation of
Application July"3`0,'1938, Serial No. 222,088l
4 Claims. (Cl. 250-11)
This invention relates to obstacle» detection and
fluency. oscillations ofthe above mentioned :Ere--
more specifically to a system in which pulses of
radio frequency energy'- are di-rectively radiated’
quency in any practical installation on an air
to be reflected by an object to be detected.
Obstacle detecting systems using radio fre
quency energy have been proposed. In one» sys
tem, a pulse of radio frequency energy» is radiatedy
toward an object and simultaneously with the ra
,obtain the required directivity for obstacle detec
tion byvutiüzing pulses of radio frequencyenergy
diation a cathode ray is deñected along one path.
of suchy construction as are practical on airplanes.
After the pulse of radio frequency energy has been
reflected by an obstacle, it is applied toV a‘receiver
which is connected to deflecting electrodes ofthe
It is afurther object of this invention to provide
means» whereby radio frequency fields navi-ngen'
overlappingportion of the required directivity for
It is an object of this invention, therefore, to
having a frequencyl of 'ther orderV of 500 mega
cycles’per second and utilizing directive antennas
cathode ray- tube so. that the. raymay be deñected>
obstacleV »detection areestabl-ishedf. Itis a stillv
at. an angle to its first mentioned path. If the cath
further object toA provide means for directively*
ode ray traverses the ñrst mentioned path at a 15 and simultaneously radiating pulses of rad-io fre-Y
uniform rate dependent upon the range of the
quency energy of,v4 different frequency indifferent
obstacle detector and startingV in. synchronism
directionsV whereby the simultaneous reception` of
with. each outgoing pulse, the- received reflected
these Waves operates a receiver responsive> to the
signals willV caues the second mentioned deñec
difference in frequency» of the pulses. A still fur
tions at points proportionalto the distance froml 20 ther obj ect of the invention is to providev` means for
distinguishing indications obtained by reflections
from obstacles locatedv on the desired coursefrom
objects to the-left lorrig-ht ofthe course.
portional to the time required for the radio Wavel
The invention will» bev described by referenceitot
to travel to the object and back to- thereceiver 25 the accompanying drawing in lwhich
and such indications are independent of direc
Figure 1 isa schematic illustration of one e tion. With such systems, the observer is unable
bodiment ofthe invention, and
‘ ,
Figures 2 and 3 are-graphicillustrations used
to distinguish between> indications resulting from
in describing the invention.
reñected Waves arriving at different. angles.. For
Referring to Fig. 1, a keyer l is connected to
example, if one reflection is caused by an object
a pair of pulse generatorsv 3, 5. The pulse gen
due north of the observer a distance of 1500 me
eratorsl have output frequencies f1 and f2, respec
ters„ an exactly similar irniication> will result
tively. AThe` output currents from the generators
from an object 1500 meters northeast of the ob
are applied respectively to the `antennas l, 9
server. One obvious correction of this` difficulty
~' which maybe dipoles or the like. The antennas
is to make the radiated Waves as directiveas pos
sible. If the obstacle detector is to be used in a
preferably include-reflectors H, i3, " The reflectors
ñxed position Where suflicient space: is available,
are of such-size and arrangement-as Will substan
it is possible to erect an antenna. array whichv will
tially prevent radiation in one direction'and Will
provide the required degree of directivity.
concentrate the radiation in the opposite> direc,
If the obstacle detecting system is to be> used
tion as Will hereinafter be described.r The keyer
the transmitter to the reflected object.
One of the difficulties» with systems. of this type»
is that the indication of the reflections is pro-y
on a relatively small vehicle suc-h as an airplane,
it becomes very difficult to erect an antenna sys
is also connected through a suitable networkl lâ
which provides a deflecting voltage for one pair
tem which will have the required directivity and
will not at the same time put unreasonable drag
of deiiecting electrodes of 'a cathode ray tube Il.
The Vkeyer may also be connected either directly
on the craft. Perhaps an obvious solution oi the
antenna array for aircrafty would be the utiliza
or through the network l5»to a receiver I9. The
input of the receiver i9 is connected to a receiv
ing antenna 2l which may'include a reñector 23.
tion of extremely high frequencies which would
permit the use of a reflector for focusing or beam
ing the Waves. While this solution is practical
from the standpoint of the, antenna. itv requiresv
the generation of Waves having a frequency of
the order of 3,000,000,000 cycles per second:
While currents of such frequencies are generated
in the laboratory, it does not. seem entirely prac.-l
ticaI toy generate, amplify and detect radio fre
In sornel installations either or both ofthe trans~
mitting antennas 1, 9 may be used as there
ceiving antenna. The output of the receiver
is connected to a second pair ofV defiecting elec
trodes; of the cathode ray tube I1;
. -
The principle of operation is as follows: The
keyer l generates pulses: which are sharply de
55 fined and of an interval of the lorder of a fraction
of a micro-second.
quency energy f1, fz having field patterns 39, 4I,
These pulses are simulta
respectively, are simultaneously radiated from
the aircraft 31. It will be seen that these field
patterns have a common or overlapping portion
43 which sharply defines the path of the craft as
represented by the dash lines 45. In the event
that there are reflecting objects as indicated by
neously applied to the pulse generators of fre
quency f1 and f2 whereby the generators are keyed
on for a brief interval. The “on interval” is fol
lowed by an “off interval” which is long enough to
permit the outgoing waves to travel to a distant
object and return before the next pulse of radio
frequency energy is radiated. The two transmit
the reference numerals 41, 49, 5I, it follows that
reflections from 41 will only contain energy of
II, I3 are arranged to direct the radiation so 10 frequency „f1 while reñections from the object
represented by reference numeral 5I will only
that the major axes of the field patterns are
contain energy of frequency f2. Since these ob
directed toward the obstacles to be detected along
jects are located at different distances from the
the course of the moving craft carrying the appa
ting antennas 1, 9, together with their reflectors
The transmitted pulses of radio frequency en
plane, the reflected energy will not arrive simul
15 taneously and will not cause any undesired
indication. If, however, an obstacle represented
by reference numeral 49 lies in the overlapping
portion of the fields, the reflected pulses f1 and f2
will reach the receiver simultaneously and will,
ergy f1 and f2 are radiated toward a distant 0b
ject to be reñected from the object back to the
receiving antenna 2| which may be made direc
tive along the desired course. The received waves
induce currents in the directive antenna 2| which 20 therefore, cause an indication. While the sys
tem of the invention thus appears to limit -itself
are applied to any suitable means for combining
to obstacles directly on the course of the plane,
the two currents to derive a current of a fre
it will appear that two objects located at equal
quency equal to the difference in frequency of
distances, although not on the desired course,
the transmitted pulses. For example, if the
transmitted pulses have a frequency f1 and f2, 25 may cause reiiections to be simultaneously re
ceived and indicated. Such a situation is prob
respectively, the pulses, after reiiection, will be
ably unlikely and would be transitory instead of
combined in the receiver to generate currents of
giving a continuous indication.
frequency f1-fz. These currents fi-fz may be
Thus. it appears that the present system simul
amplified and demodulated. The demodulated
currents are impressed on the second pair of de 30 taneously radiates impulses of two different radio
frequencies along slight different paths having a '
flecting electrodes of the cathode ray tube I1.
common field portion. The transmittedY pulses
Since the receiver is only responsive to currents
are refiected and if the reflections of the two fre
of the diiference frequency fi-fz, it follows that
the receiver will only respond when the two
duencies arrive simultaneously at the receiver.
transmitted pulses, after reflection, simultane 35 they are combined to produce an indication. AIn
ously arrive at the receiver. In the event that
the event that the pulses arrive at different times, ,
one impulse- for example f1, arrives before the
they are not combined and no indication is ob
second impulse f2, there will be no current of dif
ference frequency f1-f2 produced and therefore
no signal will appear in the output of the re
It should be understood that the receiving an
tenna may be suitably shielded to prevent direct
pickup from the transmitting antennas. In the
event that the shielding is insufficient and to
prevent any residual currents from blocking the
receiver, it is preferable to apply an initial bias
ing impulse, which may be derived directly or
indirectly from the keyer I, to make the receiver
inoperative for the brief instant at which the
radiation takes place from the transmitter. It
should also be understood that the receiver may
tained. In general~ the simultaneous reflection
will only occur in the common portion of the
overlapping iields. No attempt has been made
to describe the kever, pulse generators, cathode
ray tube or deiiecting voltage. network. as these>
elements are well known to those skilled in the,
I claim as my invention:
. _
1. In an obstacle detector system, the combina
tion oi' a keyer, a pair of pulse generators' of
radio energy of different frequency, means con
necting said keyer and said generators whereby
said generators are simultaneously keyed, means4
for directively radiating said keyed pulses of radio
energy, said radiation having diñerent field pat,
utilize a conventional radio frequency detector
terns and a portion thereof overlapping, and
and audio frequency circuits.
means for receiving said pulses after reflection,
In Fig. 2 is illustrated an aircraft 25 from 55 from said obstacle, said receiving means being
which pulses of radio frequency energy having a
responsive to currents of the difference fre
field pattern 21 are radiated. The course of the
quency of said ñrst mentioned frequencies and4
plane, with a factor of safety on either side
being unresponsive unless said currents of both
frequencies are simultaneously applied.thereof. is indicated by the dash lines 29. In the
event that objects are present at points 3i, 33 60
2. In a system of the character of claim 1 a
and 35, it Will be seen that the system would be
cathode ray tube including ray deflecting means,
responsive to reflections from all three objects.
means for deñecting said ray in synchronism
These reflections on the conventional system
with said keying, and vmeans for indicating onA
would all appear as obstacles to be avoided by
said cathode ray tube the simultaneous reception
the operator of the aircraft. However, it follows, 65 of said signals.
from inspection, that the objects represented by
3. 'I'he method of detecting objects by means
the reference numerals 3i and 35 are suiiiciently
of pulses of radio energy which includes radiat
oiï the course as to represent no obstacle in
ing pulses of radio frequency energy in different
the path of the airplane. With respect to the ob
directions, each of said pulses comprising atrain
ject indicated by the reference numeral 33, this 70 of radio frequency waves, adjusting directivity of
would represent an obstacle to be avoided.
said radiations to establish a common field, de-While the foregoing system has the charac
riving currents from the reflection of said pulses, »
teristics shown in Fig. 2, the system with this
combining said currents upon simultaneous re-.
invention has the characteristics represented by
ception, demodulating said combined currents,
Fig. 3. In this illustration pulses of radio fre 75 and indicating the presence of a pulse reflecting
object in said common field as a function of said
demodulated currents.
4. The method of detecting objects by means
of pulses of radio energy which includes, gen
quency when said simultaneous pulses are si
multaneously received, deriving from said com
bined currents a current whereof the frequency ,
erating radio currents of different frequencies,
simultaneously and directively radiating said
pulses whereby the patterns of said radiations
is equal to the difference between the frquencies
of the combind currents, demodulating said dif
ferent frequency current, and indicating the
presence of a pulse reflecting object in said com-y
have a common portion, receiving said radiated
mon portion as a function of said demodulated
pulses after reflection from an object, deriving
currents of diiîerent frequency from said recep 10
tion, combining said currents of diiîerent fre
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