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09-06-2017, 10:51 AM

I want the antenna and propagation notes by arun kumar

jaseela123d · 09-06-2017, 12:08 PM

Radio waves are easy to generate and are widely used for both indoor and outdoor communications because of their ability to traverse buildings and travel long distances.

In bands VLF, LF and MF the propagation of waves, also called as earthwaves, follow the curvature of the earth. The maximum transmission ranges of these waves are of the order of a few hundred kilometers. They are used for low bandwidth transmissions, such as amplitude modulation (AM) radio broadcasting.

The HF and VHF band transmissions are absorbed by the atmosphere, near the surface of the Earth. However, a portion of the radiation, called the sky wave, radiates outward and upward to the ionosphere in the upper atmosphere. The ionosphere contains ionized particles formed due to the radiation of the Sun. These ionized particles reflect the celestial waves back to Earth. A powerful wave of the sky can be reflected several times between the Earth and the ionosphere. Sky waves are used by amateur amateur operators and for military communication.

Propagation of radio waves

In radio communication systems, we use wireless electromagnetic waves as a channel. Antennas of different specifications can be used for these purposes. The sizes of these antennas depend on the bandwidth and frequency of the signal to be transmitted.

The mode of propagation of electromagnetic waves in the atmosphere and free space can be divided into three categories:

• Line-of-sight propagation (LOS)

• Propagation of the earthwave

• Propagation of sky waves

In the frequency bands ELF (extremely low frequency) and VLF (very low frequency), the Earth and the ionosphere act as a waveguide for the propagation of electromagnetic waves.

In these frequency ranges, communication signals are propagated practically all over the world. The channel bandwidths are small. Therefore, information is transmitted through these channels has slow speed and confined to the digital transmission.

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