U.S. patent number 3,795,910 [Application Number 05/340,871] was granted by the patent office on 1974-03-05 for microwave power transmission system wherein level of transmitted power is controlled by reflections from receiver.
This patent grant is currently assigned to The United States of America as represented by the Administrator of the. Invention is credited to William J. Robinson, Jr..
United States Patent |
3,795,910 |
Robinson, Jr. |
March 5, 1974 |
MICROWAVE POWER TRANSMISSION SYSTEM WHEREIN LEVEL OF TRANSMITTED
POWER IS CONTROLLED BY REFLECTIONS FROM RECEIVER
Abstract
A microwave, wireless, power transmission system in which the
transmitted power level is adjusted to correspond with power
required at a remote receiving station in which 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.
Inventors: |
Robinson, Jr.; William J.
(Huntsville, AL) |
Assignee: |
The United States of America as
represented by the Administrator of the (Washington,
DC)
|
Family
ID: |
23335290 |
Appl.
No.: |
05/340,871 |
Filed: |
March 13, 1973 |
Current U.S.
Class: |
342/82; 455/69;
333/17.1 |
Current CPC
Class: |
G01S
13/02 (20130101); H02J 50/20 (20160201); H02J
50/27 (20160201) |
Current International
Class: |
H02J
17/00 (20060101); G01S 13/00 (20060101); G01S
13/02 (20060101); G01s 009/02 (); H04b
003/04 () |
Field of
Search: |
;343/7.5,17.7,705
;325/4,62,159,225 ;333/17 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gensler; Paul L.
Attorney, Agent or Firm: Wofford, Jr.; L. D. Porter; G. J.
Manning; J. R.
Claims
1. A microwave power transmission system comprising:
a microwave power generator;
power supply means responsive to an input control signal for
providing variable operating power to said microwave power
generator whereby said microwave power generator is caused to
provide an output of a selected level of microwave energy;
a power transmitting antenna adapted to receive power from said
microwave power generator and direct microwave energy in an energy
beam in a selected direction;
a power receiving antenna spaced from said power transmitting
antenna and being positioned and oriented to receive maximum energy
from said transmitting 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 receiving antenna;
control means responsive to the output of said second power antenna
for providing said control signal to said power supply means;
whereby said power supply means is controlled and the output of
said microwave power generator coordinately controlled in
accordance with power
2. A microwave power transmission system as set 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
of said power receiving
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 said control signal and selected transmitter outputs for
selected values of said variable impedance load.
Description
ORIGIN OF THE INVENTION
The invention described herein was made by an employee of the
United States Government and may be manufactured and used by or for
the Government of the United States of America for governmental
purposes without the payment of any royalties thereon or
therefor.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to systems for the transmission of
electrical power by microwave radiant energy.
2. General Description of the Prior Art
It has heretofore been proposed that power be transmitted between
otherwise inaccessible locations by microwave radio transmission.
Such a method is particularly applicable to the transmission of
power through space as between earth and a space station, between
earth and the moon or between space stations. Of course, the method
is also applicable to transmission of power between locations on
earth where the cost or difficulty in building power lines makes
transmission by microwave energy feasible.
One difficulty with transmission of power by radio means,
particularly where the receiving station is not manned, is that of
transmitting correct levels of power, that is levels of power which
are needed at a particular time. This is a special problem where
there are significant variations in power load at a receiving
station. Aside from the waste, problems arise in the dissipation of
unneeded energy and in maintaining correct voltage levels.
The applicant is unaware of any previously known systems which
effectively provide desired regulation of power between the
transmitting and receiving station of such a system.
SUMMARY OF THE INVENTION
Accordingly, it is the object of this invention to provide a
microwave power transmission system in which transmitted power is
regulated in accordance with power demand and utilization at a
receiving station.
These and other objects are accomplished in the present invention
in which the transmitting station includes a receiving antenna
adapted to receive reflected or reradiated energy from the
receiving antenna of the receiving station. The reflected energy
increases with non-utilization of energy at the receiving station
and variations in received reradiated energy are detected at the
transmitting station and employed to regulate the power output of
the transmitter of the transmitting station enabling power to be
maintained at a level in accordance with actual demands of the
receiving station.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood by the following
detailed description when considered together with the accompanying
drawings in which:
FIG. 1 is a schematic illustration of a microwave power
transmission system constructed in accordance with the
invention.
FIG. 2 is a schematic illustration of a system employed for
coupling power from a receiving antenna to a load.
FIG. 3 is a schematic circuit diagram of a power control system for
translating a reradiated signal into a control signal for
controlling the power of a microwave transmitter.
FIG. 4 is a curve illustrative of the operation of the circuit
shown in FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, there is shown in FIG. 1 a block diagram
of a microwave system for transmitting electrical power between a
space transmitting station 10 and space sub-station or receiving
station 12 wherein transmitting antenna 14 and receiving antenna 16
are precisely aligned for a maximum transfer of energy and are
maintained at a precise distance apart. Transmitting station 10
employs a microwave transmitter 18 which is powered by variable or
regulatable power supply 20. Power supply 20 is controlled by power
control 22 in response to a reflected signal received by auxiliary
receiving antenna 23 indicative of the power needed by the
receiving station as represented by variable load 25. This is
accomplished as follows.
Microwave energy from transmitter 18 is fed to transmitting antenna
14 which is a narrow beam antenna such as a generally eliptical
dish-shaped antenna. This antenna is configured to transmit a
microwave beam toward receiving antenna 12. Receiving antenna 12 is
adapted to receive the transmitted power with maximum efficiency
and in accordance with one aspect of the invention would include an
array of half wave dipoles 28 supported by and spaced from
reflector 30 with dimensions appropriate to capture the maximum
amount of electromagnetic energy from transmitting station 12. A
power transmission system utilizing this general type of antenna is
disclosed in U.S. Pat. No. 3,535,543.
Referring to FIG. 2, dipoles 28 of such an antenna are each
terminated at the center by a bridge rectifier 32 which converts
radio frequency (R.F.) current to direct current. The outputs of
rectifiers 32 are fed to a summing circuit 34 wherein the outputs
are appropriately connected in a series parallel circuit
arrangement to match the impedance of variable impedance load 25,
when load 25 is operating at a maximum power level, that is in a
minimum impedance condition.
Receiving antenna 23 is a small directive antenna, mounted near,
but positioned in an R.F. null region with respect to, transmitting
antenna 14 at transmitting station 10. It samples R.F. energy
reflected by receiving antenna 16. The output of antenna 23 is
coupled to power control 22 which is adapted to provide a
calibrated output signal which is a selected proportional function
of the R.F. energy received. This output provides a control signal
input to variable power supply 20 which functions to decrease power
to transmitter 18, and thus transmitted power, to predetermined
values with increased values of reflected energy. In this manner
selected equilibrium conditions are achieved between transmitted
power and load of variable load 25, and desired amounts of power
supplied to variable load 25 for selected discrete load values.
Variable load 25 is typically representative of a combination of
powered devices connected electrically in parallel which may all be
operated at one time to provide a minimum impedance load or one or
more of the devices may be disconnected, or turned off, to provide
differing values of higher impedance. The object of this invention
is, as indicated above, to transmit less power as fewer devices are
being powered, which is signified by increases in load impedance.
In this system the quantity of energy reflected at the lowest
selected transmitted power (highest impedance-maximum antenna
mismatch combination) is greater than with maximum transmitter
power with a matched or minimum impedance condition. Thus it is
possible to provide a control system which is calibrated in terms
of a discrete value of reflected signal for a given load and power
level of transmitter 18.
FIG. 3 shows a simplified illustration of a circuit for power
control 22. Detector 36 receives R.F. energy from antenna 23 and
provides a D.C. output which is fed through limiter 38 to the plus
input of comparator 39. A reference voltage, e.g. 5 volts, is
connected across potentiometer 40 and to the plus input of
subtraction or difference circuit 42. The output of the power
control appears on moveable arm 44 of potentiometer 40 and is
applied to variable power supply 20 and to the minus output of
subtraction circuit 42. The output of the subtraction circuit is
connected to the minus input of comparator 39 and the output of the
comparator drives reversible arm 44 to thus determine circuit
output. Limiter 38, connected between detector 36 and comparator
39, limits the amplitude of signals applied to the comparator to a
maximum calibrated output of detector 36 which is equal to the
reference voltage.
FIG. 4 shows a graph of detector output voltage plotted versus
impedance load conditions. Curve 48 extends between selected
operating limits, being between minimum voltage point 50, which is
representative of reflected energy with maximum power and a matched
impedance load, and a maximum voltage point 52 which is
representative of reflected energy with a minimum power but with a
maximum impedance, and thus with a maximum impedance mismatch. The
output of detector 36 is calibrated in terms of curve 48 which
indicates a selected power output for each load value.
To examine operation of the system, it is initially assumed that
the system is in equilibrium wherein transmitter 18 is operating
with maximum power, e.g. 500 watts, to provide a desired level of
power to variable load 25 which is initially providing a matched
impedance to receiving antenna 16, e.g. 20 ohms, as shown in FIG.
4. This, as will be noted, is the minimum operating impedance value
of load 25. It is further assumed that power supply 20 provides a
level of power to transmitter 18 to achieve maximum power output
with a +4 volt input from arm 44 of potentiometer 40 and with
control arm 44 in the position shown in FIG. 4. It is further
assumed that the reflected energy from receiving antenna 16 picked
up by antenna 23, and detected by detector 36, provides detector
output of +1 volt. Thus, there will be applied to the plus input of
comparator 39 a +1 volt. The +4 volt output of control arm 44 is
applied to the minus input of subtraction circuit 42 in which this
value is subtracted from a reference +5 volts to provide a +1 volt
to the minus input of comparator 39. Thus, initially comparator 39
has equal voltages applied and it provides no output to motor 46
and thus control arm 44 is left at rest and the power level of
transmitter 18 is not changed.
It is next assumed that variable load 25 increases in impedance to
a value of, e.g. 45 ohms, indicating a decrease in need of power,
and from curve 48 it will be noted that this has been fixed at 400
watts. There will then occur an increase in reflected power from
antenna 16 which is sensed by antenna 23, causing the output of
detector 36 to rise to some value above curve 48, e.g. +3 volts as
represented by point 54. This +3 volts is applied to the plus input
of comparator 39 and with the +1 volt of the minus terminal there
is now a net +2 volts applied to the comparator resulting in a
positive output voltage. Motor 46 is then caused to rotate in a
direction to cause arm 44 to move downward. As it does, the
resulting decrease output voltage of potentiometer 40 is fed to
variable power supply 20 reducing the power output of transmitter
18 and power supplied receiving antenna 16. This in turn results in
a decrease in reflected power back to antenna 23 and to a reduced
output of detector 36. Thus there will occur a decrease in input to
the plus input of comparator 39 and an increase in input to the
minus input. This occurs since the power supply control voltage on
arm 44 decreases, representative of the power output of transmitter
18, and this voltage is subtracted from the +5 volts reference
voltage. When the voltages applied to comparator 39 are equal,
which will occur at intersection point 56 on curve 48, the output
of comparator 39 will again be made zero, turning off motor 46 and
a new desired power level will have been achieved.
Since detector 36 is appropriately compensated and calibrated as
illustrated by curve 48 to provide an output which varies generally
in proportion to load for each power setting, this means that
between the operating limits of the system, that for each load
value there exists a coordinate power level. If the power level is
too high, the output voltage of detector 36 will be above that
indicated by curve 48 and whenever there is insufficient power for
a given load, the output voltage of detector 36 will be below curve
48. If the detector output for a given load is below curve 48, the
net error voltage applied to comparator 39 will be negative and
motor 46 will be turned in a direction to cause arm 44 to provide a
higher voltage and to cause power supply 20 to effect a higher
output from transmitter 18. An opposite polarity output of detector
36 produces an opposite effect, to lower transmitter power.
It is to be appreciated that the control circuit of power control
22 illustrated in FIG. 3 is illustrative of only one circuit for
this purpose and that various systems of adjusting the power of
transmitter 18 responsive to the reflected energy from receiving
antenna 16 may be employed to provide a particular power output of
transmitter 18 for a particular load condition.
* * * * *