Question

A Hertzian dipole antenna that is small in relation to the wavelength can be shown to have radiation resistance: R_{rad} = 80pi^2 (frac{dl}{lambda})^2 where dl is the length of the antenna. A half-wavelength dipole antenna can be shown to have R_{rad}=73Omega. (a) What is meant by the term 'radiation resistance'? (b) Calculate the total radiated power from both a half-wavelength dipole antenna and a small dipole whose length is 1/20^{th} of a wavelength for an RMS input current of 10mA. (c) With reference to this result, which antenna would be better for broadcasting a radio signal? [4 marks]

          A Hertzian dipole antenna that is small in relation to the wavelength can be shown to have radiation resistance:

R_{rad} = 80pi^2 (frac{dl}{lambda})^2

where dl is the length of the antenna. A half-wavelength dipole antenna can be shown to have R_{rad}=73Omega.

(a) What is meant by the term 'radiation resistance'?

(b) Calculate the total radiated power from both a half-wavelength dipole antenna and a small dipole whose length is 1/20^{th} of a wavelength for an RMS input current of 10mA.

(c) With reference to this result, which antenna would be better for broadcasting a radio signal?

[4 marks]

$A Hertzian dipole antenna that is small in relation to the wavelength can be shown to have radiation resistance: Rrad = 80pi^2 (fracdllambda)^2 where dl is the length of the antenna. A half-wavelength dipole antenna can be shown to have Rrad=73Omega. (a) What is meant by the term 'radiation resistance'? (b) Calculate the total radiated power from both a half-wavelength dipole antenna and a small dipole whose length is 1/20^th of a wavelength for an RMS input current of 10mA. (c) With reference to this result, which antenna would be better for broadcasting a radio signal? [4 marks]$

Added by Joseph M.

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