Types of Radiofrequency (RF) Radiation
Radio waves are used in a variety of ways developed by man since the discovery of radiofrequency (RF) radiation. Among the more common types of radio-related technologies are the following:
- Public radio and television broadcasts
- Cellular communication
- Data communication (e.g. WiFi)
- Navigation transmissions, such as the Marine Navigation System, and navigation by means of satellite systems, such as the Global Positioning System (GPS), etc.
- Radar (RAdio Detection And Ranging) systems –– to detect and measure distances from objects such as airplanes or ships.
- Radio telescope for astronomical observations of astral bodies by reception of radiofrequency radiation from outer space.
The range of radiofrequency radiation in the electromagnetic radiation spectrum is divided by the International Telecommunications Union (ITU) into smaller frequency ranges, termed RF bands, allocated to different uses. For details see the RF bands in the electromagnetic spectrum in the ITU's Table of Frequencies and Uses and/or the ITU's original table.
List of main categories of radiofrequency radiation:
- Long Waves (LW): frequencies lower than 300 kHz
These waves, termed 'ground waves', are highly penetrant through the earth and are used for broadcasting across long distances. A typical antenna for transmission by long waves may reach a height of 300 meters or more. According to the ITU classification, long waves are used mainly in Europe, Africa, the Middle East, the former Soviet Union, and Mongolia. Radio transmission in these regions is performed mainly through AM (Amplitude Modulation).
- Medium Waves (MW) – range of frequencies: 500-1600 kHz
Used mainly for AM radio transmission, medium waves can travel over long distances. In the past, radio stations transmitting in this frequency range had an advantage because of their ability to transmit broadcasts to listeners in distant countries. Nowadays, medium waves are used to a limited extent today because of the ease of transmitting through transatlantic cables and the Internet. Their use is limited because of atmospheric interference in the ionosphere during the transitions between day and night and between seasons (Band 6 in the ITU's Table of Frequencies and Uses).
- Short Waves (SW) – range of frequencies: 1.7 – 30 MHz
(Bands 6-7 in the ITU's Table of Frequencies and Uses).
Short waves are used in many countries, usually by radio stations, for transmission of content broadcasts over long distances. Frequencies around 27 MHz are used for personal radio transmission. The SW range is also the source of RF signals in Magnetic Resonance Imaging (MRI) systems for non-invasive scanning in medical diagnosis and research. Another use of this range of frequencies (as in other frequency ranges described below) is for tracking and identification at exits from stores using Radio Frequency Identification (RFID) systems e.g. to prevent thefts or for automated identification of employees entering and leaving. Additional uses include: plastic welding systems, heating by induction, etc. This range of radiofrequencies is also used for communication by amateur radio adepts located in different countries.
- Very High Frequency (VHF) for radio broadcasting - range: 30-88 MHz
(Band 8 in the ITU's Table of Frequencies and Uses).
The VHF range is used for tactical communication by army radio in the Israel Defense Forces and many other armed forces throughout the world. VHF is a source of radio signals in MRI systems, and is used in Radio Frequency Identification (RFID) systems for tracking and identification (See also above, under short wave range).
- Very High Frequency (VHF) for analog radio (non-digital) broadcasting - range: 88-108 MHz
(Band 8 in the ITU's Table of Frequencies and Uses).
Also termed FM (Frequency Modulation) radio, this frequency range is used for FM transmission. It is also a source of RF signals in MRI systems and in climate radar.
- Very High Frequency (VHF) and Ultra High Frequency (UHF) for Television Broadcasting
(Bands 8-9 in the ITU's Table of Frequencies and Uses).
Very High Frequency (VHF) ranges – Analog Television: 70-88 MHz, 108-200 MHz.
Used mainly for analog TV transmission (still in use in certain countries).
Ultra High Frequency (UHF) range – Digital Television: 200-700 MHz.
Used for digital TV broadcasting, of a higher quality than analog transmission.
- Ultra High Frequency (UHF) range: 300MHz – 3GHz; Super High Frequency (SHF) range: 3 GHz-30 GHz
- Cellular communication networks, analog and digital mobile phones, and marine and aerospace radar.
(Bands 9 in the ITU's Table of Frequencies and Uses)
These frequency ranges are used by cellular base stations and for the local, urban, rural, national and international deployment of cellular networks' infrastructure–. Mobile phones generations II, III, III+ and IV (including advanced Long-Term Evolution, LTE) - operate in the 800-900 MHz, 2100 MHz, 1800-1900 MHz frequency ranges, and at high frequency around 2.6 GHz or more, respectively. Satellite radio, operates at 121.5 – 2304 MHz; tracking and identification radar systems operate in the range of 1 GHz -2.79 GHz; marine radar operates in the range of 1.55-1.65 GHz; airport radar operates in the 2-6 GHz range; military radar operates in the 1 GHz-2 GHz range (in accordance with the different bands in the ITU classification table). The more advanced radar systems may also operate at higher frequencies.
- WiFi and Bluetooth data communication– frequency ranges: 2.4 GHz, 5 GHz and others.
(Bands 9-10 in the ITU's Table of Frequencies and Uses)
WiFi frequencies are used for the transmission of data packets, mainly on the Internet. Data communication is performed according to international standard communication protocols (such as 802.11b, 802.11g and 802.11n). For example, see 802.11ac, which is the protocol for WiFi data communication in the 5 GHz range. Bluetooth also operates at high frequencies, usually at 2.4 GHz
- Wireless household telephones and microwave ovens – frequency ranges: 5.8 GHz, 2.4 GHz, 800-900 MHz.
(Bands 9-10 in the ITU's Table of Frequencies and Uses).
Technological advances introduced the use of wireless household telephones operating at these frequencies to replace landline telephones. Household microwave ovens operate at 2.4 GHz. Another rapidly developing use of these frequencies is in smart meters.
- Communication satellites and radar (super high frequency and extremely high frequency): 10 GHZ and higher
(Band 10 or higher in the ITU's Table of Frequencies and Uses)
At frequencies above 10 GHz, the penetrability of radio waves is very similar to that of light rays, i.e., any obstacle (e.g. mountains, buildings) that interferes with the passage of light waves will also largely obstruct radiofrequency radiation in this frequency range. Hence, communication at super high and extremely high frequencies above 10 GHz requires visual line of sight and necessitates more meticulous planning in the deployment density of radiation sources, to overcome the geographical obstacles and/or buildings in urban areas, and ensure better wireless communication in this frequency range. Communication in this frequency range is highly dependent on the physical and atmospheric penetrability between the transmitter and receiver.
References
- International Journal of RF Technologies: Research and Applications, (Editor-in-chief Antonio Rizzi, Prof. Ph.D. RFID Lab University of Parma Italy), ISSN print 1754-5730
- Poole I. Basic radio: principles and technology. 1998; Newnes
- Barclay LW. Propagation of radiowaves. 2nd Edition IET Electromagnetic Waves Series 502. 2003.
