Principle of Radiation-Mechanism of Radiation From Thin Wires

Principles of Radiation: Mechanism of Radiation from Thin Wires (using txn-line concepts)

Presented by APN Rao, Dept ECE, GRIET, Hyderabad. Jul 2011

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Radiation Radiation is the net outward flow of electromagnetic energy from source Radiated power is carried by free space waves, with EM fields detached from source

Accelerating (or decelerating) electric charges must radiate (Classical theory of Radiation) Presented by APN Rao, Dept ECE, GRIET, Hyderabad. Jul 2011

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Sources of Radiation Hot Objects (charged particles in rapid motion) Stars (basis of astronomy) Collisions between charged particles (braking radiation ‘Bremsstrahlung’) Charged particles travelling faster than speed of light (Cherenkov radiation)

Electrons in atoms jumping from higher to lower energy states (Quantum theory)

Time-varying currents in conductors (Linear, Surface and Volume Current Elements)


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Alternating Current Elements: The Basic Building Blocks of Antennas

Linear Current Element

I dl

Surface Current Element

J s ds

Volume Current Element

J dv


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Mechanism of Radiation from Thin Wires Equivalence between Moving Charge and Current Element

dQ v = I dL Fundamental Equation of Radiation from Thin Wires

dQ (dv/dt) = (dI/dt) dL


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Radiation from Single Wires Steady current, straight wire – No Radiation Time-harmonic current – Radiation at the frequency of oscillation Pulsed current – Radiation over broad frequency spectrum Current in curved, bent, discontinuous, terminated or truncated wire – Causes radiation

a) Curved

b)bent

d) Terminated

c) discontinuous

e) truncated


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Radiation Mechanism: 2-Wire Configuration [1/4]





Imagine the charge pattern on conductors travelling right with the voltage wave. E field lines initially attached to charges on the conductors form closed loops once every half cycle at moments of charge polarity reversal. Free space wave thus formed is not attached to the line anymore and continues to exist even if source is switched off. Presented by APN Rao, Dept ECE, GRIET, Hyderabad. Jul 2011




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Radiation from λ/2 - Dipole


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Radiation from a vertical 3λ/2 Dipole


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Dipole Antenna


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Half-Wave Dipole Antenna


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 /2 folded dipole = two centre-fed /2 dip oles, co-located


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Half-Wave Folded Dipole Antenna


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Monopole Antenna




Ground Plane

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Monopole Antenna


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Principle of Radiation-Mechanism of Radiation From Thin Wires

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