# Power of Electro Magnetic Radiation

The power of radio waves refers to the strength or intensity of the electromagnetic waves used in radio communication. It is typically measured in units like watts or milliwatts. The power of radio waves determines their range, ability to penetrate obstacles, and the quality of the received signal in radio communication systems.

### Inverse Square Law of ElectroMagnetic Radiation

We know that power of any wave be it sound or light wave reduces with increase in distance from the transmitter. Similarly, power of radio waves would also reduce with increase in distance from the transmitter. Inverse square law of ElectroMagnetic radiation defines the power required for effective range of a transmitter. Power available is inversely proportional to the square of the range. Therefore, power transmitted must be increased four times to double the range.

### Polar Diagram of a Radio Signal

Polar diagram is the line joining points of equal power or intensity of transmitted wave. Generally, a polar diagram is drawn by connecting points where the power reduces to half of its transmitted power. Polar diagram of transmitter connects points of half the power transmitted and that of a receiver connects points of half the power received.

### Effect of Shape of an Ariel or Antenna to its Polar Diagram

Shape of ariel determines the shape of polar diagram. For example, if we want all the power of to be directed in a particular direction, the ariel should be made accordingly. That’s the reason for differing size and shapes of various radar antenna.

Attenuation is the weakening of radio wave during transmission with distance. Attenuation follows inverse square law of ElectroMagnetic radiation. Attenuation of waves varies due to many factors such as frequency, polarisation, power of transmission, transmission path and the medium through which the wave is transmitted. Attenuation is of three types which are called Surface, Atmospheric and Ionospheric Attenuation.

### Surface or Ground Attenuation

Surface attenuation of radio waves refers to the weakening or loss of signal strength that occurs when radio waves travel close to or along the Earth’s surface. Factors such as ground conductivity, terrain, and obstacles can cause absorption, reflection, and scattering of the waves, reducing their power and range in surface based communication systems.

### Atmospheric Attenuation

Atmospheric attenuation causes weakening of radio waves due to atmospheric absorption and static interference. Atmospheric absorption or scatter is caused by small particles in atmosphere. Obviously, Higher frequency radio waves are affected more by atmospheric absorption. Frequencies of approximately 5 Gigahertz are affected badly by absorption since the wave length at these frequencies is almost same as size of water droplets.

### Ionospheric Attenuation of Radio Waves

Ionospheric layer is found in the upper levels of stratosphere in atmosphere. Ionosphere consists of negatively charged free electrons due to ionized gasses. Ionisation is the process of ejecting electrons from an atom. Radio waves which travel to ionosphere are refracted as well as attenuated in the Ionosphere. Ionospheric attenuation causes loss of energy in the radio wave due to collisions between wave particles and free electrons.