A microwave, wireless, power transmission system is described in which the transmitted power level is adjusted to correspond with power required at a remote receiving station. Deviations in power load produce an antenna impedance mismatch causing variations in energy reflected by the power receiving antenna employed by the receiving station. The variations in reflected energy are sensed by a receiving antenna at the transmitting station and used to control the output power of a power transmitter

Robinson, W. J., Jr.

English

NASA Technical Reports Server

REPLY TO
ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
MAR 1 4 1974
TO: KSI/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan
FROM: GP/Office of Assistant General
Counsel for patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No. :
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent case No.
J^ rJ j_
U -S- 00 UC P n iff} ev\J
NOTE - if this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable:
YES NO
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of~the—pa-tent-;- however, the name of the actual
inventor^ (author) appears at the heading of column No. 1 of
the Specification, following th^ -^ ^^ .^ . .with respect to
an invention of ..."
Bonnie L. Woerner
Enclosure
https://ntrs.nasa.gov/search.jsp?R=19740011757 2020-03-17T14:47:23+00:00Z
U.nited States Patent
Robinson, Jr.
[ i i j 3,795,910
t45) Mar. 5, 1974
[54] MICROWAVE POWER TRANSMISSION
SYSTEM WHEREIN LEVEL OF
TRANSMITTED POWER IS CONTROLLED
BY REFLECTIONS FROM RECEIVER
[75] Inventor: William J. Robinson, Jr., Huntsville,
Ala.
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
[22] Filed: Mar. 13, 1973
[21] Appl. No.: 340,871
[52] U.S. Cl 343/7.5, 325/62, 333/17,
343/17.7
[51] Int. Cl GOls 9/02, H04b 3/04
{58] Field of Search 343/7.5, 17.7, 705; 325/4,
325/62, 159,225; 333/17
[56] References Cited
UNITED STATES PATENTS
3,271,679. 9/1966 Fostoff 325/62 X
3,535,543 10/1970 Dailey 343/705 X
Primary Examiner—Paul L. Gensler
Attorney, Agent, or Firm—L. D. Wofford, Jr.; G. J.
Porter; J. R. Manning
[57] ABSTRACT
A microwave, wireless, power transmission system in
which the transmitted power level is adjusted to corre-
spond with power required at a remote receiving sta-
tion in which deviations in power load produce an an-
tenna impedance mismatch causing variations in en-
ergy reflected by the power receiving antenna em-
ployed by the receiving station. The variations in re-
flected energy are sensed by a receiving antenna at the
transmitting station and used to control the output
power of a power transmitter.
3 Claims, 4 Drawing Figures
18
MICROWAVE BEAM
-30
rTNASA-Case-MFS-21470-1) MICBOWAVE POWER
I TBftNSHISSION SYSTEM WHEBEIN LEVEL OF
, TBANSHITTED POHEB IS CONTBOLLED BY
BEFLECTIOHS FBOB BECEIVER Patent (NASA)
I CSCL 09C 00/10
N74-19870\
Dnclas
31853
PATENTED*** 5874 3.795,910
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1 2
MICROWAVE POWER TRANSMISSION SYSTEM FIG. 2 is a schematic illustration of a system em-
WHEREIN LEVEL OF TRANSMITTED POWER IS ployed for coupling power from a receiving antenna to
CONTROLLED BY REFLECTIONS FROM a load.
RECEIVER FIG. 3 is a schematic circuit diagram of a power con-
ORIGIN OF THE INVENTION 5 tro1 system for translating a reradiated signal into a
control signal for controlling the power of a microwave
The invention described herein was made by an em- transmitter.
ployee of the United States Government and may be FIG. 4 is a curve illustrative of the operation of the
manufactured and used by or for the Government of circuit shown in FIG. 3.
the United States of America for governmental pur- 10 . •
poses without the payment of any royalties thereon or DESCRIPTION OF THE PREFERRED
therefor. EMBODIMENT
BACKGROUND OF THE INVENTION Referring to the drawings, there is shown in FIG. 1 a
block diagram of a microwave system for transmitting
1. Field of the Invention 15 electrical power between a space transmitting station
This invention relates to systems for the transmission
 J0 and space sub-station or receiving station 12
of electrical power by microwave radiant energy. wherein transmitting antenna 14 and receiving antenna
2. General Description of the Prior Art
 16 aie precisely aligned for a maximum transfer of en-
It has heretofore been proposed that power be trans-
 ergy and are maintained at a precise distance apart.
milled beiween olherwise inaccessible locations by mi- 20
 Transmitting station 10 employs a microwave transmil-
crowave radio transmission. Such a method is parlicu-
 ter lg which js powered by variable or regulatable
larly applicable to the transmission of power through
 power supp,y 20 Power supp)y 2fl fa controlled by
space as between earth and a space station, between
 power contro, 22 in response to a reflected signal re-
earth and the moon or between space slalions. Of
 cejved b auxin receiving antenna 23 indicalive of
course Ihe method is also applicable to transmission of 25 ^  ^^ ^
 receivi statjon M .
power between locations on earth where the cost or d,f-
 sented fe variab,e ,oad „ Jhis .g acc ,ished as fol.
ficulty in building power lines makes transmission by .
microwave energy feasible. . Microwave energy from transmitter 18 is fed to trans-
One difficulty with transmission of power by radio
 mM antenna ^.^ js a nafrow beam antenM
means, particularly where the receiving station is not •3U , „ ,. . : .. , , , _, .
_, • u d • • . i i r such as a generally eliptical dish-shaped antenna. This
manned, is thai of transmitting correct levels of power, ." _ J ,r . r . ,
. . , ' , u- L j -i -i antenna is configured to transmit a microwave beamthai is eve s of power which are needed al a particular
 t , . .
 6
 ,,
 D • • * ,,•
-7. . • , ,, . .. • -c toward receiving antenna 12. Receiving antenna 12 istime. This is a special problem where there are sigmfi- . , ° . , 6 . .
cant variations in power load at a receiving station. adaPtedJ° receive the transrmtled power with max,-
Aside from the waste, problems arise in the dissipation 35 mum efficiency and m accordance with one aspect of
of unneeded energy and in maintaining correct vollage ths| mv,ejntlon wou'd 'ncludf an «"* of ha|f wave ^
.. poles 28 supported by and spaced from reflector 30
The' applicant is unaware of any previously known with dimensions appropriate to capture the maximum
systems which effectively provide desired regulation of amount of electromagnetic energy from transmitting
power beiween Ihe iransmilting and receiving stalion 40 statlon 12' A Power transmission syslem utilizing this
of such a system. general type of antenna is disclosed in U.S. Pat. No.
SUMMARY OF THE INVENTION 'Referring to FIG. 2, dipoles 28 of such an anlenna
Accordingly, il is Ihe object of this invention lo pro- are each terminated at the center by a bridge rectifier
vide a microwave power transmission system in which 45 32 wh'ch converts radio frequency (R.F.) current to
transmitled power is regulaled in accordance with direct current. The outputs of rectifiers 32 are fed to a
power demand and utilization at a receiving station. summing circuit 34 wherein the outpuls are appropri-
These and olher objecls are accomplished in Ihe alely connected in a series parallel circuil arrangemenl
present invenlion in which Ihe iransmilting station in- to match the impedance of variable impedance load 25,
eludes a receiving anlenna adapted lo receive reflected 50 when load 25 is operating al a maximum power level,
or reradiated energy from the receiving antenna of the that is in a minimum impedance condition,
receiving stalion. The reflected energy increases wilh Receiving anlenna 23 is a small direclive antenna,
non-utilization of energy al Ihe receiving slation and mounted near, bul posilioned in an R.F. null region
varialions in received reradiated energy are detected at with respect to, transmitting antenna 14 at iransmitling
Ihe iransmitling slation and employed to regulale Ihe slalion 10. Il samples R.F. energy reflected by receiving
power oulpul of Ihe iransmitter of Ihe iransmilling sla- anlenna 16. The oulpul of antenna 23 is coupled to
lion enabling power to be maintained at a level in ac- power control 22 which is adapted to provide a cali-
cordance with actual demands of the receiving station. brated oulpul signal which is a selected proportional
funclion of the R.F. energy received. This outpul pro-
vides a conlrol signal inpul to variable power supply 20
BRIEF DESCRIPTION OF THE DRAWINGS
 which functions to decrease power to iransmitter 18,
The invention will be more fully understood by the and ihus transmitted power, to predetermined values
following delailed ' description when considered to- wilh increased values of reflected energy. In Ihis man-
gelher wilh Ihe accompanying drawings in which:
 65 ner selected equilibrium condilions are achieved be-
FIG. 1 is a schemalic illustration of a microwave tween transmitted power and load of variable load 25,
power iransmission syslem constructed in accordance and desired amounts of power supplied to variable load
with Ihe invenlion. ... 25 for selected discrete load values.. .
3,795,910
3 4
• Variable load 25 is typically representative of a com- plied and it provides no output to motor 46 and thus
bination of powered devices connected electrically in control arm 44 is left at rest and the power level of
parallel which may all be operated at one time to pro- transmitter 18 is not changed.
vide a minimum impedance load or one or more of the It is next assumed that variable load 25 increases in
devices may be disconnected, or turned off, to provide 5 impedance to a value of, e.g. 45 ohms, indicating a de-
differing values of higher impedance. The object of this crease in need of power, and from curve 48 it will be
invention is, as indicated above, to transmit less power . noted that this has been fixed at 400 watts. There will
as fewer devices are being powered, which is signified then occur an increase in reflected power from antenna
by increases in load impedance. In this system the 16 which is sensed by antenna 23, causing the output
quantity of energy reflected at the lowest selected 10 of detector 36 to rise to some value above curve 48,
transmitted power (highest impedance-maximum an- e.g.+3 volts as represented by point 54. This+3 volts
tenna mismatch combination) is greater than with max- is applied to the plus input of comparator 39 and with
imum transmitter power with a matched or minimum the +1 volt of the minus terminal there is now a net +2
impedance condition. Thus it is possible to provide a volts applied to the comparator resulting in a positive
control system which is calibrated in terms of a discrete 15 output voltage. Motor 46 is then caused to rotate in a
value of reflected signal for a given load and power direction to cause arm 44 to move downward. As it
level of transmitter 18. does, the resulting decrease output voltage of potenti-
FIG. 3 shows a simplified illustration of a circuit for ometer 40 is fed to variable power supply 20 reducing
power control 22. Detector 36 receives R.F. energy the power output of transmitter 1.8 and power supplied
from antenna 23 and provides a D.C. output which is 20 receiving antenna 16. This in turn results in a decrease
fed through limiter 38 to the plus input of comparator in reflected power back to antenna 23 and to a reduced
39. A reference voltage, e.g. 5 volts, is connected output of detector 36. Thus there will occur a decrease
across potentiometer 40 and to the plus input of sub- in input to the plus input of comparator 39 and an in-
fraction or difference circuit 42. The output of the crease in input to the minus input. This occurs since the
power control appears on moveable arm 44 of potenti- 25 power supply control voltage on arm 44 decreases, rep-
ometer 40 and is applied to variable power supply 20 resentative of the power output of transmitter 18, and
and to the minus output of subtraction circuit 42. The this voltage is subtracted from the +5 volts reference
output of the subtraction circuit is connected to the voltage. When the voltages applied to comparator 39
minus input of comparator 39 and the output of the are equal, which will occur at intersection point 56 on
comparator drives reversible arm 44 to thus determine 30 curve 48, the output of comparator 39 will again be
circuit output. Limiter 38, connected between detector made zero, turning off motor 46 and a new desired
36 and comparator 39, limits the amplitude of signals power level will have been achieved,
applied to the comparator to a maximum calibrated Since detector 36 is appropriately compensated and
output of detector 36 which is equal to the reference calibrated as illustrated by curve 48 to provide an out-
voltage. 3^ put which varies generally in proportion to load for
FIG. 4 shows a graph of detector output voltage plot- each power setting, this means that between the operat-
ted versus impedance load conditions. Curve 48 ex- ing limits of the system, that for each load value there
tends between selected operating limits, being between exists a coordinate power level. If the power level is too
minimum voltage point 50, which is representative of high, the output voltage of detector 36 will be above
reflected energy with maximum power and a matched 40 that indicated by curve 48 and whenever there is insuf-
impedance load, and a maximum voltage point 52 ficient power for a given load, the output voltage of de-
which is representative of reflected energy with a mini- lector 36 will be below curve 48. If the detector .output
mum power, but with a maximum impedance, and thus for a given load is below curve 48, the net error voltage
with a maximum impedance mismatch. The output of applied to comparator 39 will be negative and motor 46
detector 36 is calibrated in terms of curve 48 which in- will be turned in a direction to cause arm 44 to provide
dicates a selected power output for each load value. a higher voltage and to cause power supply 20 to effect
To examine operation of the system, it is initially as- a higher output from transmitter 18. An opposite polar-
sumed that the system is in equilibrium wherein trans- ity output of detector 36 produces an opposite effect,
mitter 18 is operating with maximum power, e.g. 500 to lower transmitter power.
watts, to provide a desired level of power to variable It is to be appreciated that the control circuit of
load 25 which is initially providing a matched impe- power control 22 illustrated in FIG. 3 is illustrative of
dance to receiving antenna 16, e.g. 20 ohms, as shown only one circuit for this purpose and that various sys-
in FIG. 4. This, as will be noted, is the minimum operat- tems of adjusting the power of transmitter 18 respon-
ing impedance value of load 25. It is further assumed sive to the reflected energy from receiving antenna 16
that power supply 20 provides a level of power to trans- may be employed to provide a particular power output
mitter 18 to achieve maximum power output with a +4 of transmitter 18 for a particular load condition,
volt input from arm 44 of potentiometer 40 and with What is claimed is:
control arm 44 in the position shown in FIG. 4. It is fur- 1. A microwave power transmission system compris-
ther assumed that the reflected energy from receiving
 6Q ing:
antenna 16 picked up by antenna 23, and detected by a microwave power generator;
detector 36, provides detector output of +1 volt. Thus, power supply means responsive to an input control
there will be applied to the plus input of comparator 39 signal for providing variable operating power to
a +1 volt. The +4 volt output of control arm 44 is ap- said microwave power generator whereby said mi-
plied to the minus input of subtraction circuit 42 in
 6J crowave power generator is caused to provide an
which this value is subtracted from a reference +5 volts output of a selected level of microwave energy;
to provide a+1 volt to the minus input of comparator a power transmitting antenna adapted to receive
39. Thus, initially comparator 39 has equal voltages ap- power from said microwave power generator and
3,795,910
direct microwave energy in an energy beam in a se-
lected direction;
a power receiving antenna spaced from said power
transmitting antenna and being positioned and ori-
ented to receive maximum energy from said trans-
mitting antenna;
a variable impedance, electrical, load connected to
receive and use energy from said power receiving
antenna;
a second power receiving antenna positioned near
said transmitting antenna and adapted to receive
.electrical energy reflected from said first power re-
ceiving antenna;
control means responsive to the output of said sec-
ond power antenna for providing said control sig-
nal to said power supply means;
whereby said power supply means is controlled and
the output of said microwave power generator co-
ordinately controlled in accordance with power re-
quirements of said variable impedance load.
2. A microwave power transmission system as set
5 forth in claim 1 wherein said control means is operable
for providing variable control signals responsive to load
values variably between a load value substantially equal
to the impedance of said power receiving antenna and
a selected impedance value greater than the impedance
10 of said power receiving antenna.
3. A microwave power transmission system as set
forth in claim 2 wherein said control means includes
means responsive to selected combinations of load
impedance-power levels of the system for providing
15 said control signal and selected transmitter outputs for
selected values of said variable impedance load.
20
25
30
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40
45
50
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Microwave power transmission system wherein level of transmitted power is controlled by reflections from receiver

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