Beamed Power Transmission From Solar Power Satellites

Beamed Power Transmission from Solar Power Satellites

1. INTRODUCTION

The desire of the modern man for more and more amenities and

sophistication led to the unscrupulous exploitation of natural treasure.

Though nature has provided abundant source of resources. It is not unlimited.

Hence the exhaustion of the natural resources is eminent. The only exception

to this is sunlight.

Scientist who had understood the naked truth had thought of exploiting

the solar energy and started experimenting in this direction even from 1970.

But the progress was very slow. Much headway is yet to be made in this

direction. However as the impotents source of non-conventional energy and

due to the limited source of conventional energy emphasis has given for the

better utilization of solar energy.

But the application of solar cell, photovoltaic cell etc, we are able to

concert only a small percentage of solar energy into electrical energy. But by

using beamed power transmission from solar power satellite we can envisage

a higher percentage of conversion. By beamed power transmission, we can

extend the present system of two dimensional transmission network to three

dimensional, if does not have any environmental problem as well.

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2. SOLAR POWER SATELLITE

The solar power satellite concept would place solar power plants in

an above the earth where they could convert sunlight to electricity and beam

the ground based receiving station. The satellite would be placed in sow

called geostationary or earth synchronous orbit. 24 hour orbit that is thus

synchronous with earth rotation. so the satellite placed their will stay

stationary overhead from earths receiving antenna

The solar power satellite will consist of a large number of solar cells

mounted on a frame of steel reinforced lunarcrete. the solar cell produces

electricity from sun with no moving part. the only moving part of the satellite

is the transmitter antenna, which slowly tracks the ground based rectenna

while solar array keeps facing the sun. each transmitter antenna is connected

to solar array by two sotary joints with slip rings.

Because solar panels generate low voltage dc, super conducting

transmission line is used for transmission to microwave beamer instead of

conventional copper conductors. operating super conducting transmission

line at low voltage reduces the chance of voltage breakdown.

The vision is to generate a large Solar Power Satellite (SPS) system

for space applications. In contrast to classical designs of solar power stations,

the solar energy collected by the SPS system will not be beamed to the

Earth's surface, but used to provide for the required electrical and/or

propulsive power for vehicles in Earth orbit (LEO, MEO and GEO) and/or

deep space vehicles. Transmission of the energy to these space vehicles is

foreseen thought either beamed microwave or laser power at a power level

that can substantially rise above todays power levels up to e.g. 20-50 kW per

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space vehicle (e.g. for a

telecommunications satellite in GEO). This power is received by a relatively

low mass microwave or laser collection and rectifying system on board of the

satellite.

The use of beamed energy from a solar power satellite offers space

vehicles the advantage of omitting (part of) the heavy on-board power

generation system and or maximizing propulsive performance (in terms of

propellant consumption), thereby allowing for a reduced launch mass or an

increased payload mass. It also allows us more flexibility in the power take-

in thus providing us with a capability for e.g. short high power applications

without the need of relying on costly batteries or to reduce power without the

need to dissipate excess power. Other potential advantages for the receiving

vehicle are

Omitting the solar wings frees up two faces of the satellite for e.g. the

installation of antenna's and/or other equipment;

Reduction of thermal problems;

Less complex structure.

The physical separation of the power generation onto a separate

platform allows for an independent optimization of the power generation,

without the need to consider the spacecraft. For example, this could open up

an opportunity to operate the power satellite at very low temperatures

ensuring high solar cell efficiency or to use other (more efficient) ways of

harnessing solar power, like dynamic heat engines (o.a. Stirling engines).

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Market demands: Size, power, number of users (satellites), power

need per satellite, etc.;

Economic viability/business plan: System life, life cycle, date in

operation, laucher selection, development cost, etc.;

Efficient power conversion both at SPS and receiving satellite (e.g.

dynamic or static conversion);

High power transmission by laser and/or microwave: Size/mass of

receiver and/or transmitter, cooling requirements, etc.;

Light weight structures (flexible or rigid);

Pointing (accuracy & stability);

Orbit (LEO, GEO or other);

Impact onto space plasma environment;

Impact of space debris;

Safety (ISS, other spacecraft, launchers, etc).

As the needs of our planet's ever-increasing population grow to

unprecedented highs, the search for a new and more efficient way of

powering our industries, businesses, and homes is becoming a very pressing

priority. The techniques we use today to generate power are simply

detrimental in the long run; burning fossil fuels or splitting atoms generate a

lot of power, but also damage the planet with pollution, and alternatives like

wind and hydro power can be limited both geographically and seasonally. As

replacement technologies are pondered, one stands out. Instead of

manipulating existing elements of Earth, this inventive proposal plans to

collect solar energy from space and transmit it back to the surface using solar

power satellites (SPS). Directly harnessing the energy of the sun allows

mankind to preserve the well-being and resources of Earth while producing

enough energy to satisfy the needs of the growing human race hundreds of

times over. First proposed

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in 1968 by Dr. Peter Glaser of NASA, these satellites would use large solar

panels in space to collect the sun's light energy. Once collected, the energy

would go through two conversion phases. First, it would be sent through

onboard photovoltaic cells to be converted into electrical energy. Afterwards,

the electrical energy would be channeled into large microwave generators

where, using the principles behind the wireless power transmission of energy

(WPT), it would be converted into controllable microwaves and beamed

down to earth. On the surface, large antennas would pick up the beam and

reconvert the microwaves into electrical power, which could then be plugged

into the local power grid to use.

At first, solar power satellites were nothing more than hopeful dreams

of scientists, but recent advances have propelled them into the reaches of

reality. Satellite technology has developed to the point where

telecommunication companies use satellites for everything from cell phones

to television transmission. The WPT system has also gone through

comparable progress, especially since the development of adequate antenna

technology. Though energy conversion efficiencies from electrical energy to

microwaves and then back to electricity are currently around 54% , WPT

transmissions to a helicopter, a small aircraft, and a satellite from a launched

rocket have all been successful, demonstrating that WPT can indeed be used

to power or receive power from flying bodies. Computing technology is also

advanced enough to control satellites and allow them to change position

without interrupting a running microwave beam.

Solar power satellites are attractive ventures for many reasons.

Foremost, by using the sun, humans could acquire all the necessary energy

without causing pollution, threatening species, or generally damaging the

Earth. Second, the sun's power is limitless and perpetual. By carefully

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placing the satellites on certain points over the equator, they would be

exposed to sunlight 24 hours a day, ensuring a constant reception and flow of

energy. The power output would then only depend on how many satellites

were in space; a whole network could potentially generate exponential

amounts of usable energy. A third reason solar power is attractive is because

the constant energy flow and bulky, expensive storage facilities would no

longer be needed, minimizing costs and increasing availability. Fourth, since

there are no weather or atmospheric disturbances in space, the solar panels

would be exposed to more sunlight and have a greater efficiency than panels

placed anywhere on the Earth's surface .

Unlike x-rays or ultra-violet radiation, microwaves are non ionizing

and are one million times too weak to cause harm (SUNSAT Energy). The

only perceivable effect is heating, but since the power density of the beam

near the receivers on Earth is about 20 milliwatts per square centimeter, one-

fourth of natural sunlight, the heat generated is so slight that a person

walking through would feel nothing. Manufacturing costs are not a problem

either, since materials would be negligible Photovoltaic cells, satellite

technology and microwave beams have all been explored and researched

sufficiently to operate solar power satellites.

Solar Power in Space

Although solar energy is abundant in the inner solar system,

collecting enough of it to provide electricity for a large population of humans

is a non-trivial matter. The most comprehensive studies of large-scale solar

power generation in space were conducted over two decades ago. Legend has

it that the concept of Solar Power Satellites was first envisioned by Dr. Peter

Glaser as he sat in an early-1970's gas line. At the time there was an Arab oil

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embargo, an energy crisis, and global concern about increasing use and

decreasing availability of energy. People sometimes waited hours in lines at

the few stations that had not run out of gas, sitting in cars that got 15 miles

per gallon and had a range around 200 miles. There was plenty of time to

think.

The idea of using solar cells to generate electricity in space was nothing new.

Communications satellites had been doing that for years. Indeed, the most

distinguishing characteristics of most Earth-orbiting satellites, even today,

are their arrangements of solar cells. A common configuration is a cylindrical

shape with the entire exterior covered in purplish-blue solar cells. Non-

cylindrical satellites have large "wings" covered with solar panels. The

crewed laboratories Skylab, Mir, and International Space Station all had or

have large solar cell arrays that generate power for the satellites' use.

The difference between existing satellites and Solar Power Satellites

(SPS) is that an SPS would generate more power--much more power--than it

requires for its own operations. Studies in the 1970's by Glaser, NASA, and

major corporations produced a myriad of design concepts. Their single most

distinguishing characteristic is that they were huge-with up to 60 square

miles of surfaces covered with solar cells.A common goal of designers was to

put enough solar cells on a structure in space to generate 10 gigawatts,

approximately equal to the output of ten nuclear power plants. The idea was

not entirely far-fetched; advantages over Earth-based solar power facilities

were that the GEO locations typically proposed for SPS were almost always

in sunlight and only rarely eclipsed, and the amount of energy available to a

unit area of solar panels is seven to ten times greater than for the same area of

solar panels on Earth, because sunlight in space is not filtered by atmosphere.

Once having generated electricity in space, however, it is necessary to get the

power to where it is needed on Earth's surface. The solution selected in the

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1970's, and still valid today, was to convert power into microwave energy

that

could be beamed to Earth's surface. Microwaves pass through atmosphere,

clouds, and precipitation with no loss of energy. Experiments on Earth with

transmission and reception of energy converted to microwaves proved the

concept. The antennas designed to transmit the huge amounts of SPS power

were, however, huge (although dwarfed by the sizes of the solar panel

arrays). Typical designs were a half mile or kilometer across; examples can

be seen near the ends of the design shown in the figure.

Antenna sizes were probably dictated not so much by constraints of

materials or technology as by concern for safety. A highly concentrated

power beam would be a tough sell for people concerned about airplanes

being zapped out of the sky or entire migratory flocks of birds being cooked

en route. Large antennas in geosynchronous orbit, combined with the physics

of an expanding microwave beam, resulted in receiving antenna (rectenna)

designs six to eight miles across (10 to 13 kilometers), with maximum

intensity at the center of the microwave beam less than five times greater

than standards for kitchen emissions from a microwave oven. These facilities

would convert the microwaves back to energy, and contribute their power to

the energy grid in the same manner as a hydroelectric dam, coal-fired plant,

nuclear reactor, ground-based solar facility, geothermal plant, or field of

wind generators.

The benign radiation environments under these widely-dispersed

beams would enable air traffic, radio, TV, and birds to continue their normal

activities with no impediments. Even so, safety concerns (and the importance

of not wasting power by beaming it away from the rectenna) dictated that the

microwave beam was kept centered on the target rectenna by a "guide beam"

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reflected back to the SPS. Because the rectenna structures would be ten to

twelve feet off the ground and designed to capture all of the microwave

energy in the beam, the land under the rectenna would be available for

agriculture. It was speculated that birds would avoid the rectennas during

Summer months and congregate in them during Winter months, because they

would experience a slight warming sensation. Dr. Peter Glaser himself

offered a standing bet that he would provide fine wine and salad to the person

who would eat the first fowl to venture into the microwave beam; his point

was that the bird would be very much alive and unwilling to be eaten until

recently.

Occasional threats to energy supplies, projections that coal and oil

reserves will eventually be depleted, and concerns that burning hydrocarbons

contributes to environmental damage are providing inspiration for new

interest in Solar Power Satellites. New technologies have, however, changed

some of the parameters involved in constructing a viable SPS. Solar cells can

now convert sunlight to power much more efficiently than when the first

designs were envisioned, resulting in new designs about half the size of the

originals for the same amount of power generation. Even so, any viable SPS

of the future will still be huge.

The implication for a space settlement is that the need for power--

assuming it is provided from a solar source--will be a significant factor in the

settlement's configuration and a major feature of its design. The need to

orient solar panels toward the sun or a rectenna toward its power source will

determine how the entire settlement is positioned in space. The Space

Settlement Design Competition organizers anticipate that future non-

industrial human communities will require about 10 megawatts per 5000

people. Industrial communities will require more. The physics of microwave

transmission have not changed. Whether a space settlement is designed with

its own solar panels or with a rectenna for receiving power generated

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elsewhere in space, the equipment for providing power will be a major part

of what is seen when the settlement is viewed by approaching spacecraft.

3. PRINCIPLES OF MICROWAVE POWER TRANSMISSION SYSTEM

Schematic diagram of a beamed microwave power transmission

system is

BEAMED MICROWAVE POWER TRANSMISSION SYSTEM

70 – 90 % 70 – 97 % 5 – 95 % 85 – 92 %

MAXIMUM POSSIBLE DC TO DC EFFICIENCY ---- 76%

EXPERIMENTAL DC TO DC EFFICIENCY ----- 54%

The basic parts of a micro wave power transmission system: 1) DC to

microwave conversion (2) a beam forming antenna (3) free space

transmission and (4) reception and reconvertion to DC.

3.1 MICROWAVE POWER GENERATION

The DC power must be converted to microwave power at the

transmitting end of the system by using microwave oven magnetion. The heat

of microwave oven is the high voltage system. The nucleus of high voltage

system is the magnetron tube. The magnetron is diode type electron tube,

which uses the interaction of magnetic and electric field in the complex

BEAM FORMING ANTENNA

FREE SPACE TRANSMISSIO

N

DC TO MICROWAVE CONVERSION

RECEPTION CONVERSIO

N TO DC

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cavity to produce oscillation of very high peak power. It employs radial

electric field, axial magnetic field, anode structure and a cylindrical cathode.

The cylindrical cathode is surrounded by an anode with cavities and

thus a radial electric field will exist. The magnetic field due to two permanent

magnets which are added above end below the tube structure is axial. The

upper magnet is North Pole and lower magnet is South Pole. The electron

moving through the space tends to build up a magnetic field around itself.

The magnetic field on right side is weakened because the self-induced

magnetic field has the effect of subtracting from the permanent magnetic

field. So the electron trajectory bends in that direction resulting in a circular

motion of travel to anode. This process begins with a low voltage being

applied to the cathode, which causes it to heat up. The temperature rise

causes the emission of more electrons. This cloud of electrons would be

repelled away from the negatively charged cathode. The distance and

velocity of their travel would increase with the intensity of applied voltage.

Momentum is provided by negative 4000 V DC. This is produced by means

of voltage doubler circuit. The electrons blast off from cathode like tiny

rocket.

As the electrons move towards their objective, they encounter the

powerful magnetic. The effect of permanent magnet tends to deflect the

electrons away from the anode. Due to the combined affect of electric and

magnetic field on the electron trajectory they evive to a path at almost right

angle to their previous direction resulting in an expanding circular orbit

around the cathode, which eventually reaches the anode. The whirling cloud

of electrons forms a rotating pattern. Due to the interaction of this rotating

space chare wheel with the configuration of the surface of anode, an

alternating current of very high frequency is produced in the resonant cavities

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of the anode. The output is taken from one of these cavities through

waveguide. The low cost and readily available magnetron is used in ground.

The same principle would be used but a special magnetron would be

developed for space use. Because of the pulsed operation of these

magnetrons they generate much spurious noise. A solar power satellite

operating with 10 GW of radiated power would radiate a total power of one

microwatt in a 400 Hz channel width.

3.2 TRANSMITTING ANTENNA

The transmitting antennas are large active electronically steerable

phased array. These arrays are composed of radiation module that consists of

a high gain phased locked magnetron and directional amplifier that supplies

microwave power to slotted waveguide array.

ANATOMY OF READIATION NODULE WITH PHASE LOCKED LOOP

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The antenna must have the ability to match the transmission line

(source impedance) and load (atmosphere 377). If impedance match is

correct, the energy being transferred will be radiated into the atmosphere.

An antenna is used to convert high frequency current into

electromagnetic waves. It must have the ability to transfer energy

alternatively from electrostatic to electromagnetic.

A co axial cable is used to connect the microwave source to a

waveguide adaptor. The adaptor is connected to a ferrite circulator, which

protects the microwave source from reflected power.

A phase shifter is used to produce a difference in shift between the

radiation modules. Even though total difference in shift between radiation

modules may be great, only a low power level phase shifter of 360o is needed

in each module. Phase reference at each module is adjusted to some integral

multiple of 360o relative to the source of reference.

The slotted waveguide antenna consists of 8 waveguide section with

8 slots on each section. These 64 slots radiate power uniformly through space

to antenna in ground.

3.3 FREE SPACE TRANSMISSION

There is no economic burden for the transmission through space. The

transmitting and receiving apertures are needed for transmission. The size

and expense of this aperture has a direct relationship with the wave length

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that is being used, the distance over which energy is being sent and the

desired efficiency of transmission. The parameter T in defined as

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T =

At is the transmitter aperture area.

Ar is the receiver aperture area.

D is the separator distance between two apertures.

is the wavelength that is being used.

The relationship between aperture to efficiency and a parameter T is shown

as

This figure shows that there must be tapered distribution over

the surface of anode.

We assume that transmitter and receiver areas are equal. Under these

conditions

At = Ar = T D

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Since aperture area varies with wavelength the advantages of going to

higher frequency are diminished if the aperture areas are approximately equal

as they to be for total overall economy.

When the radiation area may be limited and a particular intensity of

the incident microwave illumination is desired; we use the expression

P = A Pt /

P is the power density at the center of receiving location.

Pt is the radiated power from transmitting antenna

Power density distributions across the transmitting and receiving

antenna aperture for various values of T are shown as:

R is the radius of transmitting or collecting antenna.

is the radial distance from the center.

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To achieve a desired valve of at the receiver site, while constrained

by a transmitted power level, the transmitting aperture area varies as the

square of the wavelength of radiation. When area available for transmitting is

limited the short wavelength are attractive.

When microwaves are used to transmit power in the vacuum of space

there is no resistive loss, no limitation to power handling probabilities. The

receiving and transmitting aperture areas sediate any waste heat resulting

from their inefficiencies directly to space. The radiation of waste heat in

space is directly proportional to the radiating area and the fourth power of

temperature at which heat is radiated. In case of the transmitter aperture in

space the relation between the microwave power per unit area to the

generator efficiency and radiating temperature is

Pr = (n/(n-1) (5.67 K T4 X 10-8)

Pr = radiated microwave power density

T = temperature in degree Kelvin.

K = emissivity of radiating surface.

n = transmission efficiency

The same expression hold for the DC power density obtained from

the receiving aperture with Pr replaced by Pdc

where Pdc is the DC power output density of rectenna.

In the figure below contours of microwave radiated power density or

DC power density from the rectenna as the functions of conversion

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efficiencies and allowed operating temperature of the coding surface that

radiate heat directly to space is shown.

This plot shows that microwave tube can handle more power density

by virtue of higher operating temperature as well as higher efficiency then

can solid-state generators. Solar power satellites are desired to operate at high

microwave power emission densities. So it is desired to operate in the center

of the transmitting array in space at a radiated micro wave power density of

25kw/m2 with a conversion efficiency of 79.5% and an operating temperature

of 300oC.

For the selection of best frequency for power transmission, the items

that would have to be considered are

The size of aperture.

The depending of overall system efficiency upon frequency.

The heat radiation problem in space.

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Whether the transmission is all in space or in path through earth

atmosphere.

Existing state of the art of available components.

The impact of the use of the selected frequency upon other users of

electromagnetic spectrum.

Transmission efficiency through the atmosphere as related to

frequency and condition of the atmosphere are shown as.

3.4 RECTENNA

The rectenna is a unique device that was conceived and developed for

beamed microwave power transmission. The functions of rectennal are power

collecting harmonic filtering and rectification into DC power. Rectenna

rectifies received microwaves into DC current. It spread out over the

receiving aperture area and combines the function of an antenna and a

rectifier. In it’s simplest from rectenna consist of a collection of rectenna

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elements, each with a half wave dipole that feeds a low pass filter circuit

terminated in a rectifying diode. The output of the diode in the local region

feeds into a common DC bus.

The efficiency can be expressed as product of three partial

efficiencies: the efficiency of the microwave beam energy intercepted by the

rectenna i, the efficiency of rectenna rectification i, and the DC power

collection circuit efficiency c.

= i r c

PHF = HF energy extracted by rectenna from the beam.

PE = is the power reedited by transmitting antenna multiplied by efficiency of

transmission line.

PRM = Sum of output DC power obtained from all RRE under the condition of

each RRE working into the matched load.

PR =DC power in the rectenna load.

The incident power flux density over the rectenna with a circular aperture

obeys the Gauss law

r = max

Where

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r is the variable radius. max is the energy flux density in the center of the rectenna

4. PROPERTIES OF MICROWAVE POWER TRANSMISSION SYSTEM.

As a mean of transferring energy from one point to another. Beamed

microwave power transmission has these features.

No mass either in the form of wire or ferrying vehicle.

Energy can be transferred at velocity of light.

The direction of energy transfer can be rapidly changed.

No energy is lost in its transfer through vacuum of space and little is

lost in the earth atmosphere at the longer microwave length.

The mass of power converters at the system terminal can be low

because of operation at microwave frequency.

Every transfer between points is independent of difference in

gravitational potential between these points.

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5. APPLICATIONS

Several applications of beamed power are

High Altitude Long Endurance (hale) aircraft.

Platforms for cellular voice and data services.

Electric powered inter orbital vehicles.

Satellite station keeping and maneuvering.

Industries in orbital and on the moon.

The demand for wireless power is likely to unfold according to the

following

Ground to special satellite.

Ground to inter orbital vehicle.

Ground to HALE platform.

Power utility satellite to inter orbital vehicle.

Power utility satellite to industry in space.

Power utility satellite to earth based consumers.

It is hoped that this technology, which at present has an efficiency of

56%, will emerge as an effective substitute for the existing technology in the

near future.

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6. CONCLUSION

The Beamed Power Transmission will surely shower the mankind

with an inexhaustible energy source and at the same time will lead to

development of in-space industries. As per the proposed design SPS and

Rectenna array are quiet efficient and would posses no threat to ecological

imbalance. There is no significant advance in this technology till now in spite

of the major research works. Once the technology is developed Power

Satellites will become the premier energy source for Earth. The sooner, the

better.

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7. REFERENCE

IEEE transactions on microwave theory and techniques, 1992

www.google. com

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ACKNOWLEDGEMENT

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ABSTRACT

Beamed micro wave power transmission may be thought of as

extending our two dimensional power transmission networks to the three

dimensional power transmission system in which power is beamed from

earth to space or power collected in space is beamed back to the earth.

Solar energy is an unlimited source of energy. The electrical energy

obtained from the sun by satellites in geostationary orbits is transmitted to

earth. Unlike x-rays or ultra-violet radiation, microwaves are non-ionizing

and are one million times too weak to cause harm (SUNSAT Energy). The

only perceivable effect is heating, but since the power density of the beam

near the receivers on Earth is about 20 milliwatts per square centimeter, one-

fourth of natural sunlight, the heat generated is so slight that a person

walking through would feel nothing. Manufacturing costs are not a problem

either since materials would be negligible (when compared with the

relatively giant profits that a solar power satellite would generate).

A complete microwave power transmission system is defined as a

three step process in which: (1) DC power at input of the system is converted

into microwave power (2) the microwave power is spread out over a

transmitting aperture (antenna), the beam formed and directed at the receiver

and (3) microwave power is captured from the beam and converted back into

DC power at the receiving location. The efficiency of the system is then

defined as the ratio of DC power output to the input.

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CONTENTS

1. INTRODUCTION 01

2. SOLAR POWER SATELLITE 02

3. PRINCIPLES OF MICROWAVE POWER TRANSMISSION SYSTEM 10

3.1 MICROWAVE POWER GENERATION 10

3.2 TRANSMITTING ANTENNA 12

3.3 FREE SPACE TRANSMISSION 13

3.4 RECTENNA 18

4. PROPERTIES OF MICROWAVE POWER TRANSMISSION SYSTEM 20

5. APPLICATIONS 21

6. CONCLUSION 22

7. REFERENCE 23

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