Define the following terms related to antennas; (i) Antenna resistance (ii) Directivity (iii) Antenna gain (iv) Power density

1 Answer

Antenna Resistance –

The resistance of an antenna has two components:

1. Its radiation resistance due to conversion of power into electromagnetic waves

2. The resistance due to actual losses in the antenna. 


The component of antenna resistance that accounts for the power radiated into space and is equal in ohms to the radiated power in watts divided by the square of the effective current in amperes at the point of power supply.

Antenna Gain – 

The directional antennae radiate more power in certain direction. The Omni-directional antenna radiates information equally in all directions. A directional antenna is said to have ‘gain’ in a particular direction. 

The directive gain can be defined in any direction. However directivity means the maximum directive gain which is obtained in only one direction in which the radiation is maximum.

Directivity = Maximum Directive gain

Power density-
The power density at any distance from an isotropic antenna is simply the transmitter power divided by the surface area of a sphere (4πR2) at that distance.
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