Antenna Theory Types of Propagation - Antenna Theory

What is Antenna Theory Types of Propagation?

In this episode, let us go over dissimilar curious topics such as the properties of radio waves, the propagation of radio waves and their types.

Radio Waves

Radio waves are cool to make and are extensively used for both indoor and outdoor communications because of their aptitude to pass over buildings and travel long distances.

The key types are −

  • Meanwhile radio transmission is Omni directional in nature, the need to actually align the transmitter and receiver does not arise.
  • The frequency of the radio wave controls numerous of the characteristics of the transmission.
  • At low frequencies, the waves can pass through problems easily. On the other hand, their power falls with an inverse-squared relation with respect to the distance.
  • The higher frequency waves are more prone to absorption by rain drops and they get reflected by obstacles.
  • Due to the long transmission range of the radio waves, interference between transmissions is a problem that needs to be addressed.

In the VLF, LF and MF bands the propagation of waves, also called as ground waves 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 engaged by the atmosphere, near the Earth's surface. On the other hand, a portion of the radiation, called the sky wave, is radiated outward and upward to the ionosphere in the upper atmosphere. The ionosphere comprises ionized elements formed due to the Sun's radiation. These ionized particles replicate the sky waves back to the Earth. A influential sky wave may be replicated several times among the Earth and the ionosphere. Sky waves are used by amateur ham radio operators and for military communication.

Radio Wave Propagation

In Radio communication systems, we use wireless electromagnetic waves as the channel. The antennas of altered specifications can be used for these purposes. The sizes of these antennas be contingent upon the bandwidth and frequency of the signal to be transmitted.

The mode of propagation of electromagnetic waves in the atmosphere and in free space may be divided in to the following three categories −

  • Line of sight (LOS) propagation
  • Ground wave propagation
  • Sky wave propagation

In ELF (Extremely low frequency) and VLF (Very low frequency) frequency bands, the Earth, and the ionosphere act as a wave guide for electromagnetic wave propagation.

In these frequency ranges, communication signals basically propagate round the world. The channel band widths are small. Hence, the information is transmitted through these channels has slow speed and limited to digital transmission.

Line of Sight (LOS) Propagation

Between the modes of propagation, this line-of-sight propagation is the one, which we usually notice. In the line-of-sight communication, as the name suggests, the wave travels a minimum distance of sight. Which means it travels to the distance up to which a naked eye can see. Now what happens after that? We need to employ an amplifier cum transmitter here to amplify the signal and transmit again.

This is well silent with the help of the resulting diagram.


line_of_sight


The figure shows this mode of propagation very obviously. The line-of-sight propagation will not be smooth if there happens any obstacle in its transmission path. As the signal can travel simply to lesser distances in this mode, this transmission is used for infrared or microwave transmissions.

Ground Wave Propagation

Ground wave propagation of the wave monitors the contour of earth. Such a wave is called as direct wave. The wave occasionally curves due to the Earth’s magnetic field and gets reproduced to the receiver. Such a wave can be termed as reflected wave.


ground_wave_propagation

The beyond figure portrays ground wave propagation. The wave when spreads through the Earth’s atmosphere is known as ground wave. The direct wave and replicated wave collectively contribute the signal at the receiver station. When the wave lastly reaches the receiver, the lags are cancelled out. In addition, the signal is filtered to avoid distortion and amplified for clear output.

Sky Wave Propagation

Sky wave propagation is ideal when the wave has to travel a longer distance. Here the wave is expected onto the sky and it is again replicated back onto the earth.

sky_wave_propagation

The sky wave propagation is well portrayed in the beyond picture. Now the waves are shown to be transmitted from one place and where it is received by numerous receivers. Therefore, it is an instance of broadcasting.

The waves, which are conveyed from the transmitter antenna, are reproduced from the ionosphere. It contains of several layers of charged atoms ranging in altitude from 30- 250 miles beyond the surface of the earth. Such a travel of the wave from transmitter to the ionosphere and from there to the receiver on Earth is known as Sky Wave Propagation. Ionosphere is the ionized layer around the Earth’s atmosphere, which is suitable for sky wave propagation.

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