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Array Gain
In array antenna systems, array gain is the measure of the improvement in signal-to-noise ratio (SNR) achieved by the array. It is calculated as the SNR of the array output signal divided by the SNR of the array input signal. Intuitively, the array gain is realized by the fact that the signal is coherently added from ''N'' array elements, while the noise is incoherently added from those same elements. If the noise is presumed to be uncorrelated the array gain is ≤ ''N'', the number of array elements, and the array gain reduces to the inverse of the square of the 2-norm of the array weight vector, under the assumption that the weight vector is normalized such that its sum is unity, so that :A = For a uniformly weighted array (un-tapered such that all elements contribute equally), the array gain is equal to ''N''. Array gain is not the same thing as "gain," "power gain," "directive gain," or "directivity," but if the noise environment around the array is isotropic and the a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Array Antenna
An antenna array (or array antenna) is a set of multiple connected antenna (radio), antennas which work together as a single antenna, to transmit or receive radio waves. The individual antennas (called ''elements'') are usually connected to a single radio receiver, receiver or transmitter by feedlines that feed the power to the elements in a specific phase (waves), phase relationship. The radio waves radiated by each individual antenna combine and Superposition principle, superpose, adding together (constructive interference, interfering constructively) to enhance the power radiated in desired directions, and cancelling (destructive interference, interfering destructively) to reduce the power radiated in other directions. Similarly, when used for receiving, the separate radio frequency currents from the individual antennas combine in the receiver with the correct phase relationship to enhance signals received from the desired directions and cancel signals from undesired directi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal-to-noise Ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. SNR is an important parameter that affects the performance and quality of systems that process or transmit signals, such as communication systems, audio systems, radar systems, imaging systems, and data acquisition systems. A high SNR means that the signal is clear and easy to detect or interpret, while a low SNR means that the signal is corrupted or obscured by noise and may be difficult to distinguish or recover. SNR can be improved by various methods, such as increasing the signal strength, reducing the noise level, filtering out unwanted noise, or using error correction techniques. SNR also determines the maximum possible amount of data that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coherence (physics)
Coherence expresses the potential for two waves to Wave interference, interfere. Two Monochromatic radiation, monochromatic beams from a single source always interfere. Wave sources are not strictly monochromatic: they may be ''partly coherent''. When interfering, two waves add together to create a wave of greater amplitude than either one (constructive Wave interference, interference) or subtract from each other to create a wave of minima which may be zero (destructive interference), depending on their relative phase (waves), phase. Constructive or destructive interference are limit cases, and two waves always interfere, even if the result of the addition is complicated or not remarkable. Two waves with constant relative phase will be coherent. The amount of coherence can readily be measured by the interference visibility, which looks at the size of the interference fringes relative to the input waves (as the phase offset is varied); a precise mathematical definition of the de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2-norm
In mathematics, a norm is a function from a real or complex vector space to the non-negative real numbers that behaves in certain ways like the distance from the origin: it commutes with scaling, obeys a form of the triangle inequality, and zero is only at the origin. In particular, the Euclidean distance in a Euclidean space is defined by a norm on the associated Euclidean vector space, called the Euclidean norm, the 2-norm, or, sometimes, the magnitude or length of the vector. This norm can be defined as the square root of the inner product of a vector with itself. A seminorm satisfies the first two properties of a norm but may be zero for vectors other than the origin. A vector space with a specified norm is called a normed vector space. In a similar manner, a vector space with a seminorm is called a ''seminormed vector space''. The term pseudonorm has been used for several related meanings. It may be a synonym of "seminorm". It can also refer to a norm that can take i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio Astronomy
Radio astronomy is a subfield of astronomy that studies Astronomical object, celestial objects using radio waves. It started in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observations have identified a number of different sources of radio emission. These include stars and galaxy, galaxies, as well as entirely new classes of objects, such as Radio galaxy, radio galaxies, quasars, pulsars, and Astrophysical maser, masers. The discovery of the cosmic microwave background radiation, regarded as evidence for the Big Bang, Big Bang theory, was made through radio astronomy. Radio astronomy is conducted using large Antenna (radio), radio antennas referred to as ''radio telescopes'', that are either used alone, or with multiple linked telescopes utilizing the techniques of Astronomical interferometer, radio interferometry and aperture synthesis. The use of interferometry allows radio astronomy to achieve high angular resolu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Decibel
The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whose level (logarithmic quantity), levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 101/20 (approximately ). The strict original usage above only expresses a relative change. However, the word decibel has since also been used for expressing an Absolute scale, absolute value that is relative to some fixed reference value, in which case the dB symbol is often suffixed with letter codes that indicate the reference value. For example, for the reference value of 1 volt, a common suffix is "#Voltage, V" (e.g., "20 dBV"). As it originated from a need to express power ratios, two principal types of scaling of the decibel are used to provide consistency depending on whether the scaling refer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diversity Gain
Diversity gain is the increase in signal-to-interference ratio due to some diversity scheme, or how much the transmission power can be reduced when a diversity scheme is introduced, without a performance loss. Diversity gain is usually expressed in decibels The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a ..., and sometimes as a power ratio. An example is soft handoff gain. For selection combining N signals are received, and the strongest signal is selected. When the N signals are independent and Rayleigh distributed, the expected diversity gain has been shown to be \sum_^\frac, expressed as a power ratio.D.G. Brennan, "Linear diversity combining techniques," Proc. IRE, vol.47, no.1, pp.1075–1102, June 1959 See also * Array gain * Diversity combining References Radio resou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
