Transcript Crossed Field Antenna

Crossed Field Antenna
Project for ELEC 522, UVIC, BC, Canada
Session - January 2002
Based On Internet Findings
Prepared by: Deepak Sarkar
Student # 0124480
Last modified: July 16, 2003
Crossed Field Antenna
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What is crossed Field Antenna?
Theory
Recent Developments
Advantages
Disadvantages
Apparent Cost Benefit
Current Worldwide Application
Future AM Antennas
Summary
• References
A CFA Operating with 100kW at
603 AM in Egypt
• The “reversed form”
(negative solution) of
Maxwell’s Fourth
Equation states that a
magnetic field can be
produced without
current flowing in a
wire. ----TRC----
Imagine an antenna!
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One–fiftieth(1/50) of a wavelength long .
Needs no radial ground system
Occupies a small parcel of land
Has great bandwidth
Produces little or no RFI (Radio Frequency
Interference)
• Performs better than a full–sized vertical
radiator
Seems like Fantasy? Isn’t it?
Working models of CFA exist in
the Middle East, Brazil,
Australia, UK and at NAB99
– Professor Dr. Maurice Hately in Scotland,
along with his student, Dr. Fathl Kabbary,
found that a magnetic field can be produced
without current flow in a wire.
– Using the reversed (negative solution) form of
Maxwell's fourth equation, they were able to
prove that a magnetic field does exist between
two capacitor plates to which a Radio
Frequency voltage has been applied.
Standard definition of
antenna
• "An antenna can be any conductive
structure that can carry an electrical
current. If it carries a time varying
electrical current, it will radiate an
electromagnetic wave."
• This definition of an antenna includes a
current carrying conductor.
Heavyside's differential form of
the third and fourth Maxwell
equations
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X E = -B’ (Faraday's law)
X H = J + D’ (Maxwell’s Modified Ampere's law)
In these equations,
' is the derivative with respect to time,
E represents the electric field strength,
B magnetic flux density = µ H,
H magnetic field strength,
J current density, and
D electric displacement (displacement current).
Essence of equations in the
last slide
( A time-varying magnetic field creates an
electric field (or back EMF)
( A current or a time-varying electric field
or both will create a magnetic field.
• Writing them in reversed form:
• B’ => -
X E
• J + D’ =>
X H (charge conservation or
charge continuity, where J +(OR) D'
as the true or total current)
The Idea makes two assertions
• Vacuum Electromagnetic Interaction The Poynting Vector represents a real power
flow even when E and H are from different
sources
• Electromagnetic Companion Wave - If
one could device a geometric configuration
of fields such that a certain space integral
becomes nonzero - a new mode of radio
communication is realized
Synthesizing the Poynting
Vector
• CFA synthesizes Poynting vector,
S = E X H,
from separately stimulated E
(electric) and H (magnetic) fields,
properly related in time, phase, and
position. S is electromagnetic radiation.
• Maintains E/H = 377 = space
impedance
Crossing effect
• To synthesize the electromagnetic wave,
radio frequency power is fed through a
power divider / phasing network to the D
and E plates.
• The resulting electric and magnetic fields
are cross–stressed in phase to synthesize the
Poynting vector, S = E X H, producing
radiated power within the small area
surrounding the antenna.
• This effect is what gives the Crossed–Field
Antenna (CFA) its name.
E & H From Different Source
. The CFA is composed of two components
that interact to produce the zone of interaction.
. The E-plate principally generates E-fields in
the near zone (ratio of E / H > 1)
. The D-plate produces H-fields (ratio of H / E
> 1) in the near zone.
. The D-plate is fed in phase-quadrature with
the E-plate maintaining correct time and
spatial relationship needed to generate the
Poynting vector (S = E x H).
Evolution Of CFA
• The barrel–shaped CFA was the first: it
featured the same radiation pattern as a
dipole.
• The next evolution removed one of the
cylinders and one of the plates, substituting
a ground plane instead.
• Subsequently, a cone was added for sky
wave depression
Sky Wave Depressor
• CFA looks like an inverted funnel from a
distance.
• The conical structure on top of the
cylindrical section is a sky wave depressor
• Sky wave components are depressed and in
fact added to the ground wave, effectively
giving the CFA an element of gain over an
antenna without this
Electric Field Strength - CFA Vs. Tower Antenna
Freq kHz
Site
Tower mV/m
CFA mV/m
225
Tanta
195
245
271
Aberdeen
190
240
279
Cairo
175
220
603
Barnis
110
165
621
Cairo
115
190
604
Tanta
150
220
882
Halaib
135
210
1125
Mansoura
150
240
CFA and Broadband
• The bandwidth of an antenna is usually
presented in terms of input impedance
and/or SWR measurements. Acceptable
SWR range for LW and MW 1 to 1.6.
• A fascinating feature of CFAs is that the
input impedance to the antenna can always
be adjusted to match any desired input
impedance at the required broadcast
frequency.
Recent Developments
• Seventeen(17) more CFA broadcast stations
in operation in Egypt, Brazil and Australia.
• UK, Germany, Italy and Malaysia are in the
process of installing new CFA antenna
• In US, CFA is awaiting FCC (Federal
Communications Commission) certification
• In US, E/H Antenna Systems developing
AM antenna based on CFA theory
Advantages over 1/4 wave length
vertical antenna
• Smaller size, 1/50th of
wave length
• High efficiency, with a
6 dB (400%) gain
• Little induction field,
very little coupling
• Broad bandwidth
• No customary ground
system
• Reduced land use
• Easier zoning approval
• Night-time broadcasts
possible due to
reduced sky-wave
• Reduced hazards for
aircraft
• Improved safety due
to lower voltage levels
of CFAs
Disadvantages
• Not well understood in • Secrecy about the
scientific community
measured data (which
could be to
• Many papers are on
monopolize the
the internet
market) makes most
discrediting inventor’s
academics suspicious
claims based on
about the theory and
numerical modeling
claims.
• Not FCC (US)
approved
• Seemingly limited
application, AM only
Apparent Cost Benefit
• If all, even some, of the claims are true:
– CFAs are cheaper considering the cost of
building and maintaining tower for lambda / 4
tower antennas
– A typical 10KW CFA, installed and tested, for
about $250,000.
– For same coverage area, a 30KW CFA antenna
is like 100KW tower antenna
World Wide Installations
• Isle of Man, UK has chosen to install a CFA
27m, 279 kHz long wave broadcast station
rather than a 845-foot (260m) tower.
• CFA antennas being tested in US for FCC
certification.
• More stations are going up in Germany,
Italy, Australia, Malaysia and Brazil
• LBA Technology Inc., NC, USA, gained
CFA Rights
Future AM Antennas
• If the Crossed–Field Antenna proves to be
everything the inventors/designers claim, it
could revolutionize the state–of–the–art in
AM transmission systems.
• EH Antenna building low cost small size
antenna implementing CFA theory
• High efficiency high gain smaller size
antennas are the future antennas
• If, CFA, theory is accepted by academics, it
may affect the world of antennas with new
food for thought!
Summary
• As interest grows around the newly found
antenna, especially for AM application,
controversy still exists regarding many
claims
• Critics argue about performance, current
distribution and radiating power, although
their arguments are based on conventional
current carrying Antenna Theory
• Among controversy, number of installations
are growing throughout the world as many
students and scholars take a close look at
the theory and the boundary conditions.
References
• Kabbary F M, Hately M C and Stewart B G - "Maxwell’s Equations
and the Crossed-Field-Antenna", Electronics and Wireless World, Vol
95, pp216-218, March (1989)
• THE CROSSED-FIELD-ANTENNA - PART I, by Maurice C.
Hately GM3HAT & Ted Hart W5QJR
• Kabbary F M, Khattab M and Hately M C - "Extremely Small High
Power MW Broadcasting Antennas", IEE International Broadcasting
Conference (IBC), Amsterdam, 10-12th September (1997)
• Hately M C and Kabbary F M US Patent No. 5155495, Radio
Antennas
• Hately M C, Kabbary F M and Stewart B G - "CFA: Working
Assumptions", Electronics and Wireless World, Vol 96, pp. 1094-1099,
December (1992)
References - Internet sites
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Www.antennex.com
www.antennex.com/shack/oct02/radmech.pdf
www.antennex.com/Stones/st0201/bstewart.pdf
www.lbagroup.com
www.lists.contesting.com/_topband/1999.April/004185.html
www.ee.surrey.ac.uk/Personal/D.Jefferies/poynting.htm
www.geocities.com/bibhasde/radiocom.htm
www.antennex.com/preview/folder03/cfameas3.htm
www.antennex.com/shack/jul00/cfacrit.htm
An idle mind is Devil’s Workshop?
An idle mind could be the
fertile ground for scientific and
social innovation workshop
too!