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Radiation Resistance Explained

Radiation Resistance (in terms of λ)

Definition

Radiation resistance represents how effectively an antenna radiates power. It can be expressed in terms of wavelength (λ).

Formula (Short Dipole)

For a short dipole antenna (l ≪ λ):

Rr = 80π² (l / λ)²

Simplified Formula

Rr ≈ 790 (l / λ)²

Since 80π² ≈ 790

Half-Wave Dipole

For a half-wave dipole antenna:

Rr ≈ 73 Ω

Example

If l = λ / 10:


Rr = 790 (1/10)²

Rr = 790 × 0.01

Rr = 7.9 Ω

Summary

Depends on (l / λ)²
Larger antenna → higher radiation resistance
Important for antenna design

Short dipole: Rr = 80π² (l / λ)²
Approx: Rr ≈ 790 (l / λ)²
Half-wave dipole: ≈ 73 Ω

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