Presentation on theme: "Crossed Field Antenna Project for ELEC 522, UVIC, BC, Canada Session - January 2002 Based On Internet Findings Prepared by: Deepak Sarkar Student # 0124480."— Presentation transcript:
Crossed Field Antenna Project for ELEC 522, UVIC, BC, Canada Session - January 2002 Based On Internet Findings Prepared by: Deepak Sarkar Student # Last modified: July 16, 2003
Crossed Field Antenna 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 Maxwells Fourth Equation states that a magnetic field can be produced without current flowing in a wire. ----TRC----
Imagine an antenna! 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? Isnt it?
–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. Working models of CFA exist in the Middle East, Brazil, Australia, UK and at NAB99
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 X E = -B ( Faraday's law) X H = J + D (Maxwells 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/mCFA mV/m 225 Tanta Aberdeen Cairo Barnis Cairo Tanta Halaib Mansoura
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 scientific community Many papers are on the internet discrediting inventors claims based on numerical modeling Not FCC (US) approved Seemingly limited application, AM only Secrecy about the measured data (which could be to monopolize the market) makes most academics suspicious about the theory and claims.
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 - "Maxwells Equations and the Crossed-Field-Antenna", Electronics and Wireless World, Vol 95, pp , 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, th September (1997) Hately M C and Kabbary F M US Patent No , Radio Antennas Hately M C, Kabbary F M and Stewart B G - "CFA: Working Assumptions", Electronics and Wireless World, Vol 96, pp , December (1992)
References - Internet sites
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