Radiation resistance is that part of an antenna's feedpoint electrical resistance that is caused by the emission of radio waves from the antenna.
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13 Facts About Radiation resistance
1.
2.
Radiation resistance is an effective resistance due to the power carried away from the antenna as radio waves.
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3.
The radiation resistance is typically defined as the value of resistance that would dissipate the same amount of power as is dissipated by the radio waves emitted from the antenna, with the same input current passing through it.
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4.
Radiation resistance is determined by the geometry of the antenna, the operating frequency, and the antenna location, and the point on the antenna at which the feedline is attached.
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5.
The cause of radiation resistance is the radiation reaction, the recoil force on the electron when it emits a radio wave photon, which reduces its momentum.
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6.
Radiation resistance is only part of the feedpoint resistance at the antenna terminals.
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7.
The total feedpoint resistance is equal to the sum of the radiation resistance and loss resistance.
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8.
Power consumed by radiation resistance is converted to radio waves, the desired function of the antenna, while the power consumed by loss resistance is converted to heat, representing a waste of transmitter power.
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9.
For "large" antennas, the radiation resistance is usually the main part of their input resistance, so it determines what impedance matching is necessary and what types of transmission line would match well to the antenna.
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10.
Since feedpoint Radiation resistance depends on the input current, it varies with the feedpoint.
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11.
Radiation resistance is usually calculated with respect to the maximum possible current in the antenna.
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12.
Radiation resistance is instead calculated by computing the far-field radiation pattern of the antenna, the power flux at each angle, for a given antenna current.
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13.
The loss resistance is in series with the radiation resistance, and as the length decreases the loss resistance only decreases in proportion to the first power of the length or remains constant, and hence makes up an increasing proportion of the feedpoint resistance.
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