86653336 Plasma Antenna Seminar Report

8/12/2019 86653336 Plasma Antenna Seminar Report

http://slidepdf.com/reader/full/86653336-plasma-antenna-seminar-report 1/34

PLASMA ANTENNA

BBDNIIT 1

Chapter 1

1. INTRODUCTION

On earth we live upon an island of "ordinary" matter. The different states

of matter generally found on earth are solid, liquid, and gas. Sir William Crookes,

an English physicist identified a fourth state of matter, now called plasma, in

1879. Plasma is by far the most common form of matter. Plasma in the stars and

in the tenuous space between them makes up over 99% of the visible universe

and perhaps most of that which is not visible. Important to ASI's technology,

plasmas are conductive assemblies of charged and neutral particles and fields

that exhibit collective effects. Plasmas carry electrical currents and generate

magnetic fields.

When the Plasma Antenna Research Laboratory at ANU investigated the

feasibility of plasma antennas as low radar cross-section radiating elements,

Redcentre established a network between DSTO ANU researchers, CEA

Technologies, Cantec Australasia and Neolite Neon for further development and

future commercialization of this technology.

The plasma antenna R & D project has proceeded over the last year at the

Australian National University in response to a DSTO (Defence Science and

Technology Organisation) contract to develop a new antenna solution that

minimizes antenna detectability by radar. Since then, an investigation of the

wider technical issues of existing antenna systems has revealed areas where

plasma antennas might be useful. The project attracts the interest of the

industrial groups involved in such diverse areas as fluorescent lighting,

telecommunications and radar. Plasma antennas have a number of potential

advantages for antenna design.

When a plasma element is not energized, it is difficult to detect by radar.

Even when it is energized, it is transparent to the transmissions above the

plasma frequency, which falls in the microwave region.



PLASMA ANTENNA

BBDNIIT 2

Chapter 2

2. PLASMA ANTENNA TECHNOLOGY

Since the discovery of radio frequency ("RF") transmission, antenna

design has been an integral part of virtually every communication and radar

application. Technology has advanced to provide unique antenna designs for

applications ranging from general broadcast of radio frequency signals for public

use to complex weapon systems. In its most common form, an antenna

represents a conducting metal surface that is sized to emit radiation at one or

more selected frequencies. Antennas must be efficient so the maximum amount

of signal strength is expended in the propagated wave and not wasted in antenna

reflection.

Plasma antenna technology employs ionized gas enclosed in a tube (or

other enclosure) as the conducting element of an antenna. This is a fundamentalchange from traditional antenna design that generally employs solid metal wires

as the conducting element. Ionized gas is an efficient conducting element with a

number of important advantages. Since the gas is ionized only for the time of

transmission or reception, "ringing" and associated effects of solid wire antenna

design are eliminated. The design allows for extremely short pulses, important to



PLASMA ANTENNA

BBDNIIT 3

many forms of digital communication and radars. The design further provides the

opportunity to construct an antenna that can be compact and dynamically

reconfigured for frequency, direction, bandwidth, gain and beam width. Plasma

antenna technology will enable antennas to be designed that are efficient, low in

weight and smaller in size than traditional solid wire antennas.

When gas is electrically charged, or ionized to a plasma state it becomes

conductive, allowing radio frequency (RF) signals to be transmitted or received.

We employ ionized gas enclosed in a tube as the conducting element of an

antenna. When the gas is not ionized, the antenna element ceases to exist. This

is a fundamental change from traditional antenna design that generally employs

solid metal wires as the conducting element. We believe our plasma antenna

offers numerous advantages including stealth for military applications and higher

digital performance in commercial applications. We also believe our technology

can compete in many metal antenna applications. Our initial efforts have focused

on military markets. General Dynamics' Electric Boat Corporation sponsored over

$160,000 of development in 2000 accounting for substantially all of our revenues.

Initial studies have concluded that a plasma antenna's performance is

equal to a copper wire antenna in every respect. Plasma antennas can be used

for any transmission and/or modulation technique: continuous wave (CW), phase

modulation, impulse, AM, FM, chirp, spread spectrum or other digital techniques.

And the plasma antenna can be used over a large frequency range up to 20GHz

and employ a wide variety of gases (for example neon, argon, helium, krypton,

mercury vapor and zenon). The same is true as to its value as a receive antenna.



PLASMA ANTENNA

BBDNIIT 4

Chapter 3

3. EXPERIMENTAL SETUP

A 100-400 Watt radio frequency source (3.7 MHz to 32 MHz) is used to

form an RF discharge in various gases, in a 35cm long and 3 cm diameter glass

tube. The glass tube is connected to a combined system of rotary and diffusion

pump. The system is evacuated to a base pressure of -5 mbar, then filled

with argon gas to various working pressures. The discharge is initiated by a

single capacitive coupler of length 3.5 cm mounted at one end of the tube. This

capacitive coupler is EM shielded. Plasma column is also formed with different

gases such as air, nitrogen and oxygen. Experiments are performed for different

plasma conditions. Surface wave is driven by 5 MHz-32 MHz frequency and 100-

400 watts input power by RF generator. Hence the column is called the surface

wave driven plasma column is shown in Fig.1.

Fig.1 Surface wave driven plasma column.



PLASMA ANTENNA

BBDNIIT 5

This plasma column acts as antenna due to surface wave induced current.

The experiment is done for showing that plasma column act as antenna, which

can be used for communication. Fig.2 shows the block diagram of

communication system with plasma antenna. In this system plasma antenna is

used for communication. Duplexer is connected 5cm above from the capacitive

coupler because 5cm is the calculated minimum distance where measurements

are not 4 affected by EM radiation by capacitive coupler. Duplexer is the

combination of Rx filter of insertion loss 0.2 dB for 49 MHz and 80 dB isolation for

46 MHz and Tx filter of insertion loss 0.2 dB for 46 MHz and isolation 80 dB for

49 MHz.

The speech or information signal of frequency 300 Hz to 3400 Hz is

generated through MIC. This signal is amplified and filtered by Audio amplifier

and filter. The tone signal of 6 KHz generated through decoders according to

hand shaking signals from singling circuit. The speech signal and handshaking

signal are mixed and fed to varac diode of X-tal oscillator for frequency

modulation. Basic frequency is 49/4 MHz, therefore oscillator frequency 12.25

MHz. This signal is passed in frequency multiplier by 4. Therefore carrier

frequency is 49 MHz is amplified and fed Tx filters of Duplexer. From plasma

antenna, 46 MHz passes through Rx filters of duplexer. This 46 MHz signal sendto Mixer. Mixer is consists of Lower oscillator (LO) which is 10.7 MHz higher than

through Low Noise Amplifier (LNA). Lower oscillator (LO) is 10.7 MHz high than

RF input and mixed. Lower oscillator gives 10.7 MHz to Intermediate frequency

(IF) filter and amplifier at 46 MHz, 10.7 MHz frequency is filtered and amplified

and again it is given to second Mixer to get 455 KHz using Lower oscillator of

(10.7 MHz + 544 KHz = 11.155 MHz) 11.155 MHz and IF of 455 KHz. Now 455

KHz IM carries information which is discriminated to get 6 KHz and 300 to 3400

Hz. Audio filter will block 6 KHz and allow 300 – 3400 Hz to go to audio amplifier

and amplified signal send to Loudspeaker. Notch filter will block all other

frequencies than 6 KHz to go to tone decoder to give signal for ring or ON/OFF

or Hook status.



PLASMA ANTENNA

BBDNIIT 6

Fig.2 BLOCK DIGRAM OF COMMUNICATION SYSTEM



PLASMA ANTENNA

BBDNIIT 7

Chapter 4

4. MARKET APPLICATIONS OF PLASMATECHNOLOGY

Plasma antennas offer distinct advantages and can compete with most metal

antenna applications. The plasma antenna's advantages over conventional metal

elements are most obvious in military applications where stealth and electronic

warfare are primary concerns. Other important military factors are weight, size

and the ability to reconfigure. Potential military applications include:

Shipboard/submarine antenna replacements.

Unmanned air vehicle sensor antennas.

IFF ("identification friend or foe") land-based vehicle antennas.

Stealth aircraft antenna replacements.

Broad band jamming equipment including for spread-spectrum emitters.

ECM (electronic counter-measure) antennas.

Phased array element replacements. EMI/ECI mitigation

Detection and tracking of ballistic missiles

Side and back lobe reduction

Military antenna installations can be quite sophisticated and just the

antenna portion of a communications or radar installation on a ship or submarine

can cost in the millions of dollars.

Plasma antenna technology has commercial applications in telemetry,

broad-band communications, ground penetrating radar, navigation, weather

radar, wind shear detection and collision avoidance, high-speed data (for

example Internet) communication spread spectrum communication, and cellular

radiation protection.



PLASMA ANTENNA

BBDNIIT 8

Chapter 5

5. MEASURMENTS AND RESULTS

5.1 CHARACTERISTICS OF PLASMA COLUMN:-

The plasma column of different gases is characterized by using standard

Langmuir probe of length 5mm and radius 0.3mm. Plasma density and electron

temperature is measured. The probe is inserted from an end of the glass tube.

The probe is manually biased from –100 to +100 volts. By evaluating the slope of

the I-V characteristics, the electron temperature is obtained. The measured valueof the density is computed from measured ion saturation current. Plasma density

eV respectively. The plasma density and temperature of all gases such as

oxygen, nitrogen, air and argon are observed to be almost same for same

external parameters and probe position. Fig.2 shows that density profile along

the axis of the glass tube. It is measured by changing the position of the probe

from one end to the other. The plasma density decreases away from the RF

exciter, placed at one end. The plasma density

Fig.3 Axial density profile



PLASMA ANTENNA

BBDNIIT 9

5.2 SURFACE WAVE DRIVEN PLASMA COLUMN:-

The plasma is formed by RF field (5 MHz to 32 MHz) at the capacitivecoupler. Surface wave excites at the interface of plasma and glass tube. There is

no external magnetic field. The plasma column of length of 35 cm is formed by

surface wave discharge. This surface wave is driven by 5 to 32 MHz frequency

and 100 to 400 watts input power by RF generator. Hence the column is called

the surface wave driven plasma column. The characterization of surface wave in

our system is given below.

The length of plasma column depends on input power used to drive the

surface wave. Fig 4 shows that the length of plasma column (0 cm to 35 cm)increases with input power (0 to 40 watt), at constant working pressure.

Fig.4 variation in length of plasma column with

input power at diff erent cosntant working

pressure and the length of glass tube is 35

cm.

The length of plasma column also depends on working pressure (.02 mbar

to .05 mbar) at constant input power, which is shown in Fig.5. the field

components of surface wave are measured by standard dipole probe and loop



PLASMA ANTENNA

BBDNIIT 10

probe on the surface of glass tube, that magnitude of electric and magnetic field

decreases along the axis of plasma column which is shown in (Fig.6).

Fig.5 Variation in length of plasma antenna with working pressure at constant

input power,w=35 watt and the length of glass tube is 35 cm.

Fig.6 Axial electric field profile on the surface of plasma antenna.



PLASMA ANTENNA

BBDNIIT 11

Azimuthal field pattern of the plasma column is measured by moving

probe in the horizontal plane around the plasma column in 15 degree increment

heights (5cm, 10cm, 15cm, 50cm) from the end

of plasma column where the source is situated. Fig.7 shows surface wave field

axisymmetric so azimuthal wave number is m=0.The power level of fundamental

harmonic decays along the axis of plasma column. This indicates damping or

attenuation of the wave inside the dielectric, which is measured by disc probe on

the surface of glass tube using spectrum analyzer. Fig.8 shows that the power

level at 5 MHz decreases from –8 dBm to –15 dBm along the axis of the plasma

column. The above experimental results show that axisymmetric electromagneticsurface wave is propagating along the interface of plasma and glass tube. It

deposits wave power to the plasma to form a 35 cm long plasma column.

Fig.7 Azimuthal f ield pattern of plasma antenna at diff erent heights f rom the

source of the plasma antenna



PLASMA ANTENNA

BBDNIIT 12

Fig.8 Variation in power level of fundamental harmonic at f =5MHz along the

axis of plasma antenna.

5.3 PLASMA COLUMNS AS MONOPOLE ANTENNA:-

This surface wave driven plasma column acts as an antenna due to

associated surface current with surface wave. Surface current is distributed on

the interface of plasma and glass tube. The axial current distribution on thesurface of plasma column is shown in Fig.9, which is measured by using shielded

and calibrated Rogowaski coil which is mounted on the outer surface of the glass

tube.

Fig.9 Current distribution on the surface of plasma column at different working

pressure



PLASMA ANTENNA

BBDNIIT 13

The magnitude of surface current depends on the plasma electron density,

which is decreasing along the axis of plasma column. As fig.9, shows the surface

current decreases along the axis of plasma antenna. This surface current which

is generated by 5 MHz driven frequency that generates electromagnetic field with

several harmonics which are shown in Fig.10.

Fig.10 Variation in power level of diff erent harmonics.

As seen clearly, higher order harmonics vanish away from the plasma

antenna due to decay of power into medium (Fig.11), measured by spectrum

analyzer. There are 20 harmonics on the surface of plasma antenna having

higher power than background power level (-80 dBm) but 60 cm away from the

antenna, there are only 2 harmonics have higher power than background power.



PLASMA ANTENNA

BBDNIIT 14

Fig.11 Number of harmonics as a f unction of radial distance

Fig.12 Elevation field pattern of plasma antenna at different Vertical planes

having 15 degree increment in azimuthal plane.



PLASMA ANTENNA

BBDNIIT 15

The elevation pattern (Fig.12) of our plasma antenna is measured by

moving the probe in an arc over the plasma Antenna Under Test (AUT) with 15-

degree increment from 00 £q £ 900 at different vertical planes and having 15

degree increment in horizontal plane. The azimuthal pattern (Fig.7) is also

measured by moving the probe in horizontal plane by 15 degree from 00 £q £

3600 at different heights (5cm, 10cm, 15cm, 50cm) from source end of the

antenna. Both these patterns are also measured in similar way for SS304 and

copper metallic antenna of similar dimensions as the plasma antennae. Patterns

are similar for the three antennae.

The Rayleigh criterion is usually taken as minimum distance from the AUT

to the far field where pattern measurements should be made. It is usually taken

to be greater then, 2L2/l where L is the largest AUT dimension. For our largest

effective antenna length (35 cm), this is about 4 mm for 5 MHz harmonic so both

patters are measured in far field region. The system dimension is much less then

wavelength (a<<l , L<<l ) where “a” is diameter (3 cm) and L is the length of

plasma antenna (35 cm). This plasma antenna will act as a monopole wire

antenna.

5.4 STRIATIONS IN PLASMA COLUMN:-

By changing external operating parameters such as working pressure (.03

mbar to 0.3 mbar), driven frequency (3.7 MHz to 32 MHz), input power (70 watt

to 400 watt), background pressure (10-3 mbar to 10-6 mbar) and length of glass

tube (5 cm to 30 cm), plasma column is transformed to finite number of

cylindrical or spherical striations (balls), helical plasma with rotation and plasma

with spiral shape. These states are visibly different and are shown in

photographs (Fig.13, 14,15). These different structures in plasma column aretransformed from a stable uniform inhomogeneous steady state (plasma column)

to unstable nonuniform inhomogeneous state, which again diffuses to stable

nonuniform inhomogenous observed steady state.



PLASMA ANTENNA

BBDNIIT 16

Fig.13 Planer array plasma antenna

Fig.14 Helical plasma antenna.



PLASMA ANTENNA

BBDNIIT 17

Fig.15 Spiral plasma antenna

5.5 STATIONARY STRIATIONS AS ARRAY PLASMA ANTENNA:-

At critical value which is the combination of input power and working

pressure (Fig.16) these cylindrical striations are separated from each other. The

separation between striations will be vanished at lower and higher value then the

critical value. Now each cylindrical striation forms a short length plasma column

having associated surface current so each cylindrical plasma element of plasma

column acts as a short antenna. These segments or elements of plasma antenna

are called antenna elements. The axial current distribution on the antenna

elements is shown in Fig.17. These different formations in the plasma are visible

at different pressures or power, keeping all other remaining parameters constant.



PLASMA ANTENNA

BBDNIIT 18

Fig.16 Critical value of input power at various working pressures to form plasma antenna elements.

Fig.17 Current distribution on the surface of planar array plasma antenna



PLASMA ANTENNA

BBDNIIT 19

The parameters of antenna elements can be controlled such that number

and length of elements vary by changing the working pressure, power, driven

frequency and length of glass tube. Fig.18 shows that the number of antenna

elements increase with driven frequency and input power. The number of

elements vary from six to ten by operating at 5MHz, 100 watts of power to 32

MHz and 400 watts of power. Fig.19 shows that the number of elements are

increasing from one to six while the length of glass tube is varied from 5 cm to 30

cm. The length of first antenna element varies with driven frequency. It is 5 cm at

5 MHz and 2 cm at 32 MHz. The length of antenna elements decreases along

the antenna axis (Fig.20). This structure of plasma antenna acts as a planner

array antenna. Some other structures (Helical and Spiral) are also found in ourexperiment, are shown in Fig.14 and 15. These structures of plasma act as

antenna, which can be called Helical plasma antenna and spiral plasma antenna.



PLASMA ANTENNA

BBDNIIT 20

Fig. 18, 19 Variation in number of plasma antenna element with driven frequency

& along the length of the glass tube



PLASMA ANTENNA

BBDNIIT 21

Fig.21 Variation in length of antenna elements as a function of number of

antenna elements at different working presser

5.6 EXPERIMENTS FOR VERSATILE PLASMA ANTENNA:-

Qualitative observations have been confirmed that the plasma antenna

can be used for transmitting and receiving audio signals or TV (video)

information. Two experiments, given below to show that plasma structures act as

receiving/transmitting antenna over the range 10 to 250 MHz for a range of RF

power levels and hence different effective length and structures for antenna.

(I) Jamming capabilities of EM waves of this antenna has been qualitatively

tested with standard FM radio receivers at 91.90 MHz. This FM channel could be

received in the absence of plasma column even though rf generator is kept ON.

But the effective range is measured as 170 cm away from plasma antenna when

plasma is formed, the reception of FM radio channel is cut off. This experiment is

performed by all structures of plasma antenna.

(II) The audio noise level is measured on the loudspeaker output terminal. The

noise level is measured with different structures of plasma antenna, which

formed as working pressure and without plasma in glass tube. The noise level is

reduced from 15.2 mV to 8.7 mV, Fig.22 shows clearly, the noise level is



PLASMA ANTENNA

BBDNIIT 22

reducing with pressure and plasma antenna structure is also changing with

pressure so the planner array antenna and helical plasma antenna performs

better than the monopole plasma antenna. This plasma antenna acts as a

receiver when audio frequency (300-3400 Hz) which is converted to carrier

frequency (46-49 MHz) frequency multiplier and RF amplifier so the plasma

antenna works as Tx/Rx antenna. Plasma antenna is used for communication.

The communication range of our monopole plasma antenna is measured to be

45 meters, which is increased up to 60 meters with varying pressure or different

structure of plasma antenna, In comparison the communication range with a

similar metallic telescope antenna is measured as 50 meters. The

communication range increases with different structures. All these structures ofplasma act as antenna. Different type of antenna structures is formed in a single

system by changing the external parameters, so it can be named as a versatile

plasma antenna.

Fig.21 Variation in noise level with working pressure



PLASMA ANTENNA

BBDNIIT 23

Chapter 6

6.RADIATION PATTERN

The radiation pattern of the tube working as an antenna is measured by a

standard transmitter-receiver system `Signet Antenna Analyzing Equipment's (S-

99R, S-99T, S-99V)'. The schematic experimental set up for this purpose is

shown in Figure 22. The radiation pattern is measured in the H plane

(perpendicular to the antenna).

Figure22. Picture of Plasma antenna on the Signet receiver.

Figure 23. Schematic picture showing the antenna with respect to the Trans-

mitting system in the co polar position.



PLASMA ANTENNA

BBDNIIT 24

A 3 element Yagi antenna is taken as the transmitter to radiate at 590 MHz.

The plasma antenna is mounted on the revolving machine and connected to the

receiver. For each 1 degree, the receiver measures the power received by the

plasma antenna in dB micro Volt (dB¹V) and stores it in the internal array

memory. Two such arrays (of 360 points each) are provided. The observed

pattern is shown in Figure 24 for frequency 590 MHz. Both curves are polar plots,

showing angular variation of the normalized received power. The outer circle has

a constant value 0 dB in this scale, and the inner circle has a value ¡10 dB. The

measurement, with reference to Figure 22, is done for one particular polarization

of the transmitter (or one particular transmitter) at a time, for a full rotation of 360

degree of the receiver. First measurement is referred to as Àrray 1', as shownon the upper left panel of Figure 10. We can mark two cursors on the Array 1

curve that show the received power in dB¹V at those particular angle values, as

shown on the lower left panel of Figure 24. In our measurement, Array 1 curve,

marked À', is for co-polarization. The rst cursor shows the maximum value of

received power having a value 73.4 dB at 193 degree, while the second cursor

shows the minimum value of received power having a value 59.0 dB at 24

degree. The second measurement referred to as Àrray 2' is for a cross

polarization between the transmitter and plasma antenna, and this curve is

marked `B'. No cursors can be marked on this, as it has to be analyzed relative to

the Array 1 results. Also, it can be seen from Figure 24 that from angle 0 degree

to 60 degree, the received power values are approximately equal in both co- and

cross-polarizations. This happens due to scattering of fields from the coaxial

cable because it comes in between the transmitting and receiving antennas. This

coaxial cable has been used for power supply to the upper electrode of the

fluorescent tube.



PLASMA ANTENNA

BBDNIIT 25

Figure 24. Radiation from the plasma antenna shows monopole patterns.



PLASMA ANTENNA

BBDNIIT 26

Chapter 7

7. UNIQUE CHARACTERISTICS OF A PLASMAANTENNA

One fundamental distinguishing feature of a plasma antenna is that the

gas ionizing process can manipulate resistance. When demonized, the gas has

infinite resistance and does not interact with RF radiation. When demonized the

gas antenna will not backscatter radar waves (providing stealth) and will not

absorb high-power microwave radiation (reducing the effect of electronic warfare

countermeasures). A second fundamental distinguishing feature is that after

sending a pulse the plasma antenna can be demonized, eliminating the ringing

associated with traditional metal elements. Ringing and the associated noise of a

metal antenna can severely limit capabilities in high frequency short pulse

transmissions. In these applications, metal antennas are often accompanied by

sophisticated computer signal processing. By reducing ringing and noise, we

believe our plasma antenna provides increased accuracy and reduces computer

signal processing requirements. These advantages are important in cutting edge

applications for impulse radar and high-speed digital communications. Based onthe results of development to date, plasma antenna technology has the following

additional attributes:

No antenna ringing provides an improved signal to noise ratio and

reduces multipath signal distortion.

Reduced radar cross section provides stealth due to the non-metallic

elements.

Changes in the ion density can result in instantaneous changes in

bandwidth over wide dynamic ranges. After the gas is ionized, the plasma antenna has virtually no noise floor.

While in operation, a plasma antenna with a low ionization level can be

decoupled from an adjacent high-frequency transmitter.

A circular scan can be performed electronically with no moving parts at a

higher speed than traditional mechanical antenna structures.



PLASMA ANTENNA

BBDNIIT 27

It has been mathematically illustrated that by selecting the gases and

changing ion density that the electrical aperture (or apparent footprint) of a

plasma antenna can be made to perform on par with a metal counterpart

having a larger physical size.

Our plasma antenna can transmit and receive from the same aperture

provided the frequencies are widely separated.

Plasma resonance, impedance and electron charge density are all

dynamically reconfigurable. Ionized gas antenna elements can be

constructed and configured into an array that is dynamically reconfigurable

for frequency, beam width, power, gain, polarization and directionality - on

the fly. A single dynamic antenna structure can use time multiplexing so that

many RF subsystems can share one antenna resource reducing the

number and size of antenna structures.



PLASMA ANTENNA

BBDNIIT 28

Chapter 8

8. SPONSORED WORK

To date, plasma antenna technology has been studied and characterized

by ASI Technology Corporation revealing several favorable attributes in

connection with antenna applications. The work was carried out in part through

two ONR sponsored contracts. NCCOSC RDTE Division, San Diego, awarded

contract N66001-97-M-1153 1 May 1997. The major objective of the program

was to determine the noise levels associated with the use of gas plasma as a

conductor for a transmitting and receiving antenna. Both laboratory and field-test

measurements were conducted. The second contract N00014-98- C-0045 was a

6-month SBIR awarded by ONR on November 15, 1997. The major objective of

this effort was to characterize the GP antenna for conductivity, ionization

breakdowns, upper frequency limits, excitation and relaxation times, ignition

mechanisms, temperatures and thermionic noise emissions and compare these

results to a reference folded copper wire monopole. The measured radiation

patterns of the plasma antenna compared very well with copper wire antennas.

ASI Technology Corporation is under contract with General Dynamics

Electric Boat Division and in conjunction with the Plasma Physics Laboratory at

the University of Tennessee, an inflatable plasma antenna is being developed.

This antenna is designed to operate at 2.4 Ghz and would be mounted on the

mast of an attack submarine. In addition a prototype plasma waveguide and

plasma reflector has been designed and demonstrated to General Dynamics.

The following discussion illustrates why there is military and government

support for plasma antenna concepts. The gas plasma antenna conducts

electron current like a metal and hence can be made into an antenna but with

distinct advantages. The following technological concepts are important to

plasma antennas:



PLASMA ANTENNA

BBDNIIT 29

1. Higher power - Increased power can be achieved in the plasma antenna than

in the corresponding metal antenna because of lower Ohmic losses. Plasmas

have a much wider range of power capability than metals as evident from low

powered plasma in fluorescent bulbs to extremely high-powered plasmas in the

Princeton University experimental fusion reactors. In this range, a high-powered

plasma antenna is still low powered plasma. Since plasmas do not melt, the

plasma antennas can provide heat and fire resistance. The higher achievable

power and directivity of the plasma antenna can enhance target discrimination

and track ballistic missiles at the S and X band.

2. Enhanced bandwidth - By the use of electrodes or lasers the plasma density

can be controlled. The theoretical calculations on the controlled variation of

plasma density in space and time suggest that greater bandwidth of the plasma

antenna can be achieved than the corresponding metal antenna of the same

geometry. This enhanced bandwidth can improve discrimination.

3. EMI/ECI - The plasma antenna is transparent to incoming electromagnetic

signals in the low density or turned off mode. This eliminates or diminishes

EMI/ECI thereby producing stealth. Several plasma antennas can have their

electron densities adjusted so that they can operate in close proximity and one

antenna can operate invisible to others. In this physical arrangement mutual side

lobe and back lobe clutter is highly reduced and hence jamming and clutter is

reduced.

4. Higher efficiency and gain - Radiation efficiency in the plasma antenna is

higher due to lower Ohmic losses in the plasma. Standing wave efficiency is

higher because phase conjugate matching with the antenna feeds can be

achieved by adjusting the plasma density and can be maintained during

reconfiguration. Estimates indicate a 20db improvement in antenna efficiency.

5. Reconfiguration and mutifunctionality - The plasma antenna can be

reconfigured on the fly by controlled variation of the plasma density in space and

time with far more versatility than any arrangement of metal antennas. This

reduces the number of required elements reducing size and weight of shipboard

antennas. One option is to construct controlled density plasma blankets around



PLASMA ANTENNA

BBDNIIT 30

plasma antennas thereby creating windows (low-density sections of the blanket)

for main lobe transmission or reception and closing windows (high-density

regions in the plasma blanket). The plasma windowing effect enhances directivity

and gain in a single plasma antenna element so that an array will have less

elements than a corresponding metal antenna array. Closing plasma windows

where back lobes and side lobes exist eliminates them and reduces jamming and

clutter. This sidelobe reduction below 40db enhances directivity and

discrimination. In addition, by changing plasma densities, a single antenna can

operate at one bandwidth (e.g. communication) while suppressing another

bandwidth (e.g. radar).

6. Lower noise - The plasma antenna has a lower collision rate among its

charge carriers than a metal antenna and calculations show that this means less

noise.

7. Perfect reflector - When the plasma density is high the plasma becomes a

loss-less perfect reflector. Hence there exist the possibilities of a wide range of

lightweight plasma reflector antennas.



PLASMA ANTENNA

BBDNIIT 31

Chapter 9

9. ADVANTAGES

The advantage of a plasma antenna is that it can appear and disappear in

a few millionths of a second. This means that when the antenna is not required, it

can be made to disappear, leaving behind the gas – filled column that has little

effect on the electromagnetic fields in the proximity of the tube. The same will be

true for fiber glass and plastic tubes, which are also under consideration.

The other advantage of plasma antenna is that even when they areionized and in use at the lower end of the radio spectrum, say HF

communications, they are still near transparent to fields at microwave

frequencies.

The same effect is observed with the use of ionosphere, which is plasma.

Every night amateur radio operators bounce their signals off the ionosphere to

achieve long distance communications, whilst microwave satellite communication

signals pass through the ionosphere.



PLASMA ANTENNA

BBDNIIT 32

CONCLUSION

As part of a “blue skies” research program, DSTO has teamed up with the

ANU’s Plasma Research Laboratory to investigate the possibility of using

plasmas like those generated in fluorescent ceiling lights, for antennas.

The research may one day have far reaching applications from robust

military antennas through to greatly improve external television aerials. Antennas

constructed of metal can be big and bulky, and are normally fixed in place. The

fact that metal structures cannot be easily moved when not in use limits some

aspects of antenna array design. It can also pose problems when there is a

requirement to locate many antennas in a confined area.

Weapons System Division has been studying the concept of using plasma

columns for antennas, and has begun working in collaboration with ANU plasma

physicists Professor Jeffrey Harris and Dr. Gerard Borg. Work by the team has

already led to a provisional patent and has generated much scientific interest as

it is so novel. It offers a paradigm shift in the way we look at antennas and is

already providing the opportunity to create many new and original antenna

designs.

Plasma is an ionized gas and can be formed by subjecting a gas to strong

electric or magnetic fields. The yellow lights in streets are a good example of

plasmas though a better example is the fluorescent tubes commonly used for

lighting in homes.

The type of plasma antenna under investigation is constructed using a

hollow glass column which is filled with an inert gas. This can be ionized by the

application of a strong RF field at the base of the column. Once energized, theplasma column can be made to exhibit many of the same characteristics of a

metal whip antenna of the type mounted on most cars. The metal whips that may

be considered for a plasma replacement are anywhere from a few centimeters to

several meters long.



PLASMA ANTENNA

BBDNIIT 33

There are many potential advantages of plasma antennas, and DSTO and

ANU are now investigating the commercialization of the technology. Plasma

antenna technology offers the possibility of building completely novel antenna

arrays, as well as radiation pattern control and lobe steering mechanisms that

have not been possible before. To date, the research has produced many novel

antennas using standard fluorescent tubes and these have been characterized

and compare favorably with their metal equivalents. For example, a 160 MHz

communications link was demonstrated using plasma antennas for both base

and mobile stations. Current research is working towards a robust plasma

antenna for field demonstration to Defense Force personnel.



PLASMA ANTENNA

REFERENCES

A.W.Trivelpiece and R.W.Gould, J.Appl.Phys.,30, 1784(1959)

A.W.Trivelpiece , slow-wave propagation in plasma waveguids, San

Francisco University Press)

A.Shivarova and I. Zhelyazkov, Plasma Phys., 20,1049(1978).

M. Moisan , A. Shivarova and A. W. Trivelpiece, Plasma

Phys.,24,1331(1982)

D. R. Tuma, Rev.Sci.Instrum.,41, 1519(1970)

Z. Zakrzewski, M. Moisan, V. M. M. Glade, C. Beaudry and P. Leprince,

Plasma Phys.,19,77(1977).

M. Moisan and Z. Zakrzewski, Rev.Sci.Instrum.,58,1895(1986).

G. G. Borg, J. H. Harris, D. J. Miljak and N. M. Martin, Apll.Phys.Lett., 74,

3272(1999).

P. Whichello, J. P. Rayner and A. D. Cheetham, Proc.11th Int. Conf.

Plasma Physics, Sydney, Australia, 396(July-2002).

J. P. Rayner, A. P. Whichello, and D. Cheetham, IEEE Trans.Plasma

Sci.,32(1), 269 (2004).

G. G. Borg, J. H. Harris, N.M. Martin, D. Thorncraft, R. Milliken, D. G.

Miljak, B. Kwan, T. Ng. and J. Kircher, Phys. Plasmas, 7,2198 (July 2000)

H. S. Robertson and J. J. Herring, Phys. Fluids 12, 836 (1969).

Date post:	03-Jun-2018
Category:	Documents
Upload:	arunav-singh
View:	222 times
Download:	1 times

86653336 Plasma Antenna Seminar Report

Documents