The World Health Organization (WHO) has researched electromagnetic fields (EMFs) and their alleged effects on health, concluding that such exposures within recommended limits do not produce any known adverse health effect.
In response to public concern, the WHO established the International EMF Project in 1996 to assess the scientific evidence of possible health effects of EMF in the frequency range from 0 to 300 GHz. They have stated that although extensive research has been conducted into possible health effects of exposure to many parts of the frequency spectrum, all reviews conducted so far have indicated that, as long as exposures are below the limits recommended in the ICNIRP (1998) EMF guidelines, which cover the full frequency range from 0–300 GHz, such exposures do not produce any known adverse health effect. Stronger or more frequent exposures to EMF can be unhealthy, and in fact serve as the basis for electromagnetic weaponry.
International guidelines on exposure levels to microwave frequency EMFs such as ICNIRP limit the power levels of wireless devices and it is uncommon for wireless devices to exceed the guidelines. These guidelines only take into account thermal effects, as nonthermal effects have not been conclusively demonstrated. The official stance of the British Health Protection Agency (HPA) is that “[T]here is no consistent evidence to date that WiFi and WLANs adversely affect the health of the general population”, but also that “...it is a sensible precautionary approach...to keep the situation under ongoing review...”.
In 2011, International Agency for Research on Cancer (IARC), an agency of the World Health Organization, classified wireless radiation as Group 2B – possibly carcinogenic. That means that there "could be some risk" of carcinogenicity, so additional research into the long-term, heavy use of wireless devices needs to be conducted.
Users of wireless devices are typically exposed for much longer periods than for mobile phones and the strength of wireless devices is not significantly less. Whereas a Universal Mobile Telecommunications System (UMTS) mobile phone can range from 21 dBm (125 mW) for Power Class 4 to 33 dBm (2W) for Power class 1, a wireless router can range from a typical 15 dBm (30 mW) strength to 27 dBm (500 mW) on the high end.
However, wireless routers are typically located significantly farther away from users' heads than a mobile phone the user is handling, resulting in far less exposure overall. The Health Protection Agency (HPA) says that if a person spends one year in a location with a Wi-Fi hotspot, they will receive the same dose of radio waves as if they had made a 20-minute call on a mobile phone.
The HPA also says that due to the mobile phone's adaptive power ability, a DECT cordless phone's radiation could actually exceed the radiation of a mobile phone. The HPA explains that while the DECT cordless phone's radiation has an average output power of 10 mW, it is actually in the form of 100 bursts per second of 250 mW, a strength comparable to some mobile phones.
Most wireless LAN equipment is designed to work within predefined standards. Wireless access points are also often close to people, but the drop off in power over distance is fast, following the inverse-square law. However, wireless laptops are typically used close to people. WiFi had been anecdotally linked to electromagnetic hypersensitivity but research into electromagnetic hypersensitivity has found no systematic evidence supporting claims made by sufferers.
The HPA's position is that “...radio frequency (RF) exposures from WiFi are likely to be lower than those from mobile phones.” It also saw “...no reason why schools and others should not use WiFi equipment.” In October 2007, the HPA launched a new “systematic” study into the effects of WiFi networks on behalf of the UK government, in order to calm fears that had appeared in the media in a recent period up to that time". Dr Michael Clark, of the HPA, says published research on mobile phones and masts does not add up to an indictment of WiFi.
In telecommunications and radar engineering, antenna boresight is the axis of maximum gain (maximum radiated power) of a directional antenna. For most antennas the boresight is the axis of symmetry of the antenna. For example, for axial-fed dish antennas, the antenna boresight is the axis of symmetry of the parabolic dish, and the antenna radiation pattern (the main lobe) is symmetrical about the boresight axis. Most antennas boresight axis is fixed by their shape and cannot be changed. However phased array antennas can electronically steer the beam, changing the angle of the boresight by shifting the relative phase of the radio waves emitted by different antenna elements, and even radiate beams in multiple directions (multiple boresights).The term boresight came from high-gain antennas such as parabolic dishes, which produce narrow, pencil-shaped beams which are difficult to aim accurately at a distant receiving antenna. These often are equipped with optical boresights to assist in aiming.Antenna efficiency
In antenna theory, antenna efficiency is most often used to mean radiation efficiency. In the context of antennas, one often just speaks of "efficiency." It is a measure of the electrical efficiency with which a radio antenna converts the radio-frequency power accepted at its terminals into radiated power. Likewise, in a receiving antenna it describes the proportion of the radio wave's power intercepted by the antenna which is actually delivered as an electrical signal. It is not to be confused with aperture efficiency which applies to aperture antennas such as the parabolic reflector.Antenna equivalent radius
The equivalent radius of an antenna conductor is defined as:
where denotes the conductor's circumference, is the length of the circumference, and are vectors locating points along the circumference, and and are differentials segments along it. The equivalent radius allows the use of analytical formulas or computational or experimental data derived for antennas constructed from small conductors with uniform, circular cross-sections to be applied in the analysis of antennas constructed from small conductors with uniform, non-circular cross-sections. Here "small" means the largest dimension of the cross-section is much less than the wavelength .Antenna factor
In electromagnetics, the antenna factor is defined as the ratio of the electric field strength to the voltage V (units: V or µV) induced across the terminals of an antenna. The voltage measured at the output terminals of an antenna is not the actual field intensity due to actual antenna gain, aperture characteristics, and loading effects.
For an electric field antenna, the field strength is in units of V/m or µV/m and the resulting antenna factor AF is in units of 1/m:
If all quantities are expressed logarithmically in decibels instead of SI units, the above equation becomes
For a magnetic field antenna, the field strength is in units of A/m and the resulting antenna factor is in units of A/(Vm). For the relationship between the electric and magnetic fields, see the impedance of free space.
For a 50 Ω load, knowing that PD Ae = Pr = V2/R and E2= PD ~ 377PD (E and V noted here are the RMS values averaged over time), the antenna factor is developed as:
For antennas which are not defined by a physical area, such as monopoles and dipoles consisting of thin rod conductors, the effective length is used to measure the ratio between E and V.Antenna height considerations
The Aspects for Antenna heights considerations are depending upon the wave range and economical reasons.Antenna rotator
An antenna rotator is a device used to change the orientation, within the horizontal plane, of a directional antenna. Most antenna rotators have two parts, the rotator unit and the controller. The controller is normally placed near the equipment which the antenna is connected to, while the rotator is mounted on the antenna mast directly below the antenna.
Rotators are commonly used in amateur radio and military communications installations. They are also used with TV and FM antennas, where stations are available from multiple directions, as the cost of a rotator is often significantly less than that of installing a second antenna to receive stations from multiple directions.
Rotators are manufactured for different sizes of antennas and installations. For example, a consumer TV antenna rotator has enough torque to turn a TV/FM or small ham antenna. These units typically cost around US$70.
Heavy-duty ham rotators are designed to turn extremely large, heavy, high frequency (shortwave) beam antennas, and cost hundreds or possibly thousands of dollars.
In the center of the reference picture, the accompanying image includes an AzEl installation rotator, so named for its controlling of both the azimuth and the elevation components of the direction of an antenna system or array. Such antenna configurations are used in, for example, amateur-radio satellite]] or moon-bounce communications.
An open hardware AzEl rotator system is provided by the SatNOGS Groundstation project.Array gain
In MIMO communication systems, array gain means a power gain of transmitted signals that is achieved by using multiple-antennas at transmitter and/or receiver, with respect to single-input single-output case. It can be simply called power gain. In a broadside array, the array gain is almost exactly proportional to the length of the array. This is the case provided that the elements of the antenna are not spaced to a point at which large radiation side lobes form in other directions and that the array length exceeds one or two wavelengths. The power gain of a broadside array is nearly independent of the number of broadside elements as long as both of these conditions are met.The two main types of array gain when combining signals are average power of combined signals relative to the individual average power and the diversity gain related to the probability level of outage. The diversity gain is dependent on spatial correlation coefficients between antenna signals.Beam steering
Beam steering (also spelled beamsteering or beam-steering) is about changing the direction of the main lobe of a radiation pattern.
In radio and radar systems, beam steering may be accomplished by switching the antenna elements or by changing the relative phases of the RF signals driving the elements.
In acoustics, beam steering is used to direct the audio from loudspeakers to a specific location in the listening area. This is done by changing the magnitude and phase of two or more loudspeakers installed in a column where the combined sound is added and cancelled at the required position. Commercially, this type of loudspeaker arrangement is known as a line array. This technique has been around for many years but since the emergence of modern DSP (Digital Signal Processing) technology there are now many commercially available products on the market. Beam Steering and Directivity Control using DSP was pioneered in the early 1990s by Duran Audio who launched a technology called DDC (Digital Directivity Control).
In optical systems, beam steering may be accomplished by changing the refractive index of the medium through which the beam is transmitted or by the use of mirrors, prisms, lenses, or rotating diffraction gratings. Examples of optical beam steering approaches include mechanical mirror-based gimbals or beam-director units, galvanometer mechanisms that rotate mirrors, Risley prisms, phased-array optics, and microelectromechanical systems (MEMS) using micro-mirrors.
Source: from Federal Standard 1037CBell Laboratories Layered Space-Time
Bell Laboratories Layer Space-Time (BLAST) is a transceiver architecture for offering spatial multiplexing over multiple-antenna wireless communication systems. Such systems have multiple antennas at both the transmitter and the receiver in an effort to exploit the many different paths between the two in a highly-scattering wireless environment. BLAST was developed by Gerard Foschini at Lucent Technologies' Bell Laboratories (now Alcatel-Lucent Bell Labs). By careful allocation of the data to be transmitted to the transmitting antennas, multiple data streams can be transmitted simultaneously within a single frequency band — the data capacity of the system then grows directly in line with the number of antennas (subject to certain assumptions). This represents a significant advance on current, single-antenna systems.Block upconverter
A block upconverter (BUC) is used in the transmission (uplink) of satellite signals. It converts a band of frequencies from a lower frequency to a higher frequency. Modern BUCs convert from the L band to Ku band, C band and Ka band. Older BUCs convert from a 70 MHz intermediate frequency (IF) to Ku band or C band.
Most BUCs use phase-locked loop local oscillators and require an external 10 MHz frequency reference to maintain the correct transmit frequency.
BUCs used in remote locations are often 2 or 4 W in the Ku band and 5 W in the C band. The 10 MHz reference frequency is usually sent on the same feedline as the main carrier. Many smaller BUCs also get their direct current (DC) over the feedline, using an internal DC block.
BUCs are generally used in conjunction with low-noise block converters (LNB). The BUC, being an up-converting device, makes up the "transmit" side of the system, while the LNB is the down-converting device and makes up the "receive" side. An example of a system utilizing both a BUC and an LNB is a VSAT system, used for bidirectional Internet access via satellite.
The block upconverter is a block shaped device assembled with the LNB in association with an OMT, orthogonal mode transducer to the feed-horn that faces the reflector parabolic dish. This is opposed to other types of frequency upconverter which may be rack mounted indoors or not co-located with the dish.Focal cloud
A focal cloud is the collection of focal points of an imperfect lens or parabolic reflector whether optical, electrostatic or electromagnetic. This includes parabolic antennas and lens-type reflective antennas of all kinds. The effect is analogous to the circle of confusion in photography.
In a perfect lens or parabolic reflector, rays parallel to the device's axis striking the lens or reflector all pass through a single point, the focal point. In an imperfectly constructed lens or reflector, rays passing through different parts of the element do not converge to a single point but have different focal points. The set of these focal points forms a region called the focal cloud. The diameter of the focal cloud determines the maximum resolution of the optical system. Lens-reflector artifacts, geometry and other imperfections determine the actual diameter of the focal cloud.Main lobe
In a radio antenna's radiation pattern, the main lobe, or main beam, is the lobe containing the higher power. This is the lobe that exhibits the greater field strength.
The radiation pattern of most antennas shows a pattern of "lobes" at various angles, directions where the radiated signal strength reaches a maximum, separated by "nulls", angles at which the radiation falls to zero. In a directional antenna in which the objective is to emit the radio waves in one direction, the lobe in that direction is designed to have higher field strength than the others, so on a graph of the radiation pattern it appears biggest; this is the main lobe. The other lobes are called "sidelobes", and usually represent unwanted radiation in undesired directions. The sidelobe in the opposite direction from the main lobe is called the "backlobe".
The radiation pattern referred to above is usually the horizontal radiation pattern, which is plotted as a function of azimuth about the antenna, although the vertical radiation pattern may also have a main lobe. The beamwidth of the antenna is the width of the main lobe, usually specified by the half power beam width (HPBW), the angle encompassed between the points on the side of the lobe where the power has fallen to half (-3 dB) of its maximum value.
The concepts of main lobe and sidelobes also apply to acoustics and optics, and are used to describe the radiation pattern of optical systems like telescopes, and acoustic transducers like microphones and loudspeakers.Mobile phone radiation and health
The effect of mobile phone radiation on human health is a subject of interest and study worldwide, as a result of the enormous increase in mobile phone usage throughout the world. As of 2015, there were 7.4 billion subscriptions worldwide, though the actual number of users is lower as many users own more than one mobile phone. Mobile phones use electromagnetic radiation in the microwave range (450–3800 MHz and 24-80GHz in 5G mobile). Other digital wireless systems, Such as data communication networks, produce similar radiation.
The World Health Organization states that "A large number of studies have been performed over the last two decades to assess whether mobile phones pose a potential health risk. To date, no adverse health effects have been established as being caused by mobile phone use." In a 2018 statement, the FDA said that "the current safety limits are set to include a 50-fold safety margin from observed effects of Radio-frequency energy exposure".Passive radiator
In a radio antenna, a passive radiator or parasitic element is a conductive element, typically a metal rod, which is not electrically connected to anything else. Multielement antennas such as the Yagi-Uda antenna typically consist of a "driven element" which is connected to the radio receiver or transmitter through a feed line, and parasitic elements, which are not. The purpose of the parasitic elements is to modify the radiation pattern of the radio waves emitted by the driven element, directing them in a beam in one direction, increasing the antenna's directivity (gain). A parasitic element does this by acting as a passive resonator, something like a guitar's sound box, absorbing the radio waves from the nearby driven element and re-radiating them again with a different phase. The waves from the different antenna elements interfere, strengthening the antenna's radiation in the desired direction, and cancelling out the waves in undesired directions.Radiation resistance
Radiation resistance is that part of an antenna's feedpoint resistance that is caused by the radiation of electromagnetic waves from the antenna, as opposed to loss resistance (also called ohmic resistance) which is caused by ordinary electrical resistance or other losses in the antenna, which dissipates energy as heat.
The energy depleted by loss resistance is converted to heat radiation; the energy lost by radiation resistance is converted to radio waves. When the feedpoint is at a voltage minimum, the total of radiation resistance and loss resistance is the electrical resistance of the antenna. The ratio of the radiation resistance to the total resistance is the antenna efficiency.
The radiation resistance is determined by the geometry of the antenna, whereas the loss resistance is primarily determined by the materials of which it is made and its distance from and alignment with other conductors nearby, and what they are made of. Both radiation and loss resistance depend on the distribution of current in the antenna.Reconfigurable antenna
A reconfigurable antenna is an antenna capable of modifying its frequency and radiation properties dynamically, in a controlled and reversible manner. In order to provide a dynamic response, reconfigurable antennas integrate an inner mechanism (such as RF switches, varactors, mechanical actuators or tunable materials) that enable the intentional redistribution of the RF currents over the antenna surface and produce reversible modifications of its properties. Reconfigurable antennas differ from smart antennas because the reconfiguration mechanism lies inside the antenna, rather than in an external beamforming network. The reconfiguration capability of reconfigurable antennas is used to maximize the antenna performance in a changing scenario or to satisfy changing operating requirements.Spurious emission
A spurious emission is any radio frequency not deliberately created or transmitted, especially in a device which normally does create other frequencies. A harmonic or other signal outside a transmitter's assigned channel would be considered a spurious emission.
From ITU, 1.145 Spurious emission: Emission on a frequency or frequencies which are outside the
necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products but exclude out-of-band emissions.WSDMA
WSDMA (Wideband Space Division Multiple Access) is a high bandwidth channel access method, developed for multi-transceiver systems such as active array antennas. WSDMA is a beamforming technique suitable for overlay on the latest air-interface protocols including WCDMA and OFDM. WSDMA enabled systems can determine the angle of arrival (AoA) of received signals to spatially divide a cell sector into many sub-sectors. This spatial awareness provides information necessary to maximise Carrier to Noise+Interference Ratio (CNIR) link budget, through a range of digital processing routines. WSDMA facilitates a flexible approach to how uplink and downlink beamforming is performed and is capable of spatial filtering known interference generating locations.World Radiocommunication Conference
World Radiocommunication Conference (WRC) is organized by ITU to review and as necessary, revise the Radio Regulations, the international treaty governing the use of the radio-frequency spectrum and the geostationary-satellite and non-geostationary-satellite orbits. It is held every three to four years. Prior to 1993, it was called the World Administrative Radio Conference (WARC); in 1992, at an Additional Plenipotentiary Conference in Geneva, the ITU was restructured, and later conferences became the WRC.At the 2015 conference (WRC-15), the ITU deferred their decision on whether to abolish the leap second to 2023.The next World Radiocommunication Conference (WRC-19) will take place from 28 October to 22 November 2019 in Sharm el-Sheikh, Egypt.
Radiation (physics and health)