Department of Applied Sciences, Amity University Uttar Pradesh, Uttar Pradesh, Lucknow, India
Received: 08-Sep-2022 Manuscript No. JPAP-22-74288; Editor assigned: 12-Sep-2022, Pre QC No. JPAP-22-74288 (PQ); Reviewed: 26-Sep-2022, QC No. JPAP-22-74288; Revised: 03-Oct-2022, Manuscript No. JPAP-22-74288 (A) Published: 10-Oct-2022, DOI:10.4172/2320-2459.10.6.002.
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Typically occurring at frequencies of 300 Gigahertz (GHz) and below, radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum. At 300 GHz, the wavelength is 1 mm, which is shorter than a grain of rice, while at 30 Hz; the wavelength is 10,000 kilometres (6,200 miles) (longer than the radius of the Earth). Radio waves move at the speed of light in a vacuum, as do all electromagnetic waves, and at a nearly identical speed in the Earth's atmosphere. Naturally occurring radio waves are emitted by lightning and astronomical objects and are a component of the blackbody radiation that is given off by all warm objects. Radio waves are produced by charged particles that are accelerating, such as time-varying electric currents. Because of their large wavelength, radio waves have more favourable propagation properties than other electromagnetic waves, which make them more widely used for communication.
Radio waves can pass through the atmosphere in any weather, through foliage and most building materials, and by diffraction, they can bend around obstructions. Additionally, unlike other electromagnetic waves, they tend to be scattered rather than absorbed by objects larger than themselves. In order to design useful radio systems, it is crucial to understand radio propagation, or how radio waves move through space and across the surface of the Earth. Radio waves undergo reflection, refraction, polarization, diffraction, and absorption as they move through various environments. Different radio bands are more advantageous for particular uses than others because they experience different combinations of these atmospheric phenomena. Three different radio propagation techniques are primarily used by practical radio systems for communication:
Line of sight
This refers to radio waves that travel in a straight line from the transmitting antenna to the receiving antenna. Radio waves can travel through foliage, buildings, and other obstructions at lower frequencies, so a clear line of sight is not always necessary. At frequencies higher than 30 MHz, this is the only propagation technique that is practical. The visual horizon restricts line of sight propagation to about 64 km on Earth's surface (40 mi). Cell phones, FM radio, television broadcasting, and radar all employ this technique. Point-to-point microwave relay links transmit telephone and television signals over great distances, up to the visual horizon, by using dish antennas to transmit microwave beams. Satellites and spacecraft can communicate with ground stations from billions of miles away.
Indirect propagation: Diffraction and reflection allow radio signals to reach points outside the line of sight. Radio waves bend around barriers such as a building edge, a car, or a turn in a hall due to diffraction. Surfaces such as walls, floors, ceilings, automobiles, and the ground also partially reflect radio waves. These types of propagation are used in short-range radio communication systems like cell phones, cordless phones, walkie-talkies, and wireless networks. One disadvantage of this mode is multipath propagation, which occurs when radio waves travel from the sending antenna to the receiving antenna through several routes. The waves often interact, resulting in fading and other reception issues.
Due to diffraction, vertically polarized radio waves can bend over hills and mountains and propagate beyond the horizon at lower frequencies below 2 MHz in the medium and long wave bands, travelling as surface waves that follow the shape of the Earth. This allows medium wave and long wave broadcasting stations to have coverage ranges that extend hundreds of miles beyond the horizon. As the frequency decreases, so do the losses and the possible range. Military Very Low Frequency (VLF) and Extremely Low Frequency (ELF) communication devices can connect with submarines hundreds of meters beneath the sea.
Radio waves at medium and shortwave wavelengths bounce off conductive layers of charged particles (ions) in the ionosphere, a region of the atmosphere. As a result, radio waves projected into the sky at an angle might return to Earth beyond the horizon this is known as skip or sky wave propagation. Communication over long distances can be accomplished by using numerous skips. Sky wave propagation is erratic and weather dependent. It is most reliable at night and in the winter. Sky wave communication was widely utilized in the early half of the twentieth century, but due to its unreliability, it was generally abandoned. Military Over-The-Horizon (OTH) radar systems, some automated systems, radio amateurs, and shortwave broadcasting stations continue to use it to broadcast to other countries.