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Grating Lobes
For discrete aperture antennas (such as phased arrays) in which the element spacing is greater than a half wavelength, a spatial aliasing effect allows plane waves incident to the array from visible angles other than the desired direction to be coherently added, causing grating lobes. Grating lobes are undesirable and identical to the main lobe. The perceived difference seen in the grating lobes is because of the radiation pattern of non-isotropic antenna elements, which affects main and grating lobes differently. For isotropic antenna elements, the main and grating lobes are identical. Definition In antenna or transducer arrays, a grating lobe is defined as "a lobe other than the main lobe, produced by an array antenna when the inter-element spacing is sufficiently large to permit the in-phase addition of radiated fields in more than one direction." Derivation To illustrate the concept of grating lobes, we will use a simple uniform linear array. The beam pattern (or ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Typical Antenna Pattern With Grating Lobes
Typical may refer to: * ''Typical'' (album), Peter Hammill * "Typical" (song), song by MuteMath *"Typical", song by Frazier Chorus from ''Sue'', 1987 *''Typical'', story collection by Padgett Powell Padgett Powell (born April 25, 1952 in Gainesville, Florida) is an American novelist in the Southern literary tradition. His debut novel, ''Edisto'' (1984), was nominated for thNational Book Awardand was excerpted in ''The New Yorker''. Powell ..., 1991 * Typical, song by Raven-Symoné from '' This Is My Time'', 2004 See also *'' Typical Rick'', an American Comedy Central television series {{dab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phased Array
In antenna (radio), antenna theory, a phased array usually means an electronically scanned array, a computer-controlled Antenna array, array of antennas which creates a radio beam, beam of radio waves that can be electronically steered to point in different directions without moving the antennas. In a phased array, the power from the transmitter is fed to the radiating elements through devices called ''phase shifters'', controlled by a computer system, which can alter the phase or signal delay electronically, thus steering the beam of radio waves to a different direction. Since the size of an antenna array must extend many wavelengths to achieve the high gain needed for narrow beamwidth, phased arrays are mainly practical at the high frequency end of the radio spectrum, in the ultrahigh frequency, UHF and microwave bands, in which the operating wavelengths are conveniently small. Phased arrays were originally invented for use in military radar systems, to detect fast moving pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aliasing
In signal processing and related disciplines, aliasing is a phenomenon that a reconstructed signal from samples of the original signal contains low frequency components that are not present in the original one. This is caused when, in the original signal, there are components at frequency exceeding a certain frequency called Nyquist frequency, f_s / 2, where f_s is the sampling frequency ( undersampling). This is because typical reconstruction methods use low frequency components while there are a number of frequency components, called aliases, which sampling result in the identical sample. It also often refers to the distortion or artifact that results when a signal reconstructed from samples is different from the original continuous signal. Aliasing can occur in signals sampled in time, for instance in digital audio or the stroboscopic effect, and is referred to as temporal aliasing. Aliasing in spatially sampled signals (e.g., moiré patterns in digital images) is referre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phased Array Radiation Pattern
A phaser is an electronic sound processor used to filter a signal by creating a series of peaks and troughs in the frequency spectrum. The position of the peaks and troughs of the waveform being affected is typically modulated by an internal low-frequency oscillator so that they vary over time, creating a sweeping effect. Phasers are often used to give a "synthesized" or electronic effect to natural sounds, such as human speech. Process The electronic phasing effect is created by splitting an audio signal into two paths. One path treats the signal with an all-pass filter, which preserves the amplitude of the original signal and alters the phase. The amount of change in phase depends on the frequency. When signals from the two paths are mixed, the frequencies that are out of phase will cancel each other out, creating the phaser's characteristic notches. Changing the mix ratio changes the depth of the notches; the deepest notches occur when the mix ratio is 50%. The def ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uniform Linear Array
A uniform is a variety of costume worn by members of an organization while usually participating in that organization's activity. Modern uniforms are most often worn by armed forces and paramilitary organizations such as police, emergency services, security guards, in some workplaces and schools, and by inmates in prisons. In some countries, some other officials also wear uniforms in their duties; such is the case of the Commissioned Corps of the United States Public Health Service or the French prefects. For some organizations, such as police, it may be illegal for non-members to wear the uniform. Etymology From the Latin ''unus'' (meaning one), and ''forma'' (meaning form). Variants Corporate and work uniforms Workers sometimes wear uniforms or corporate clothing of one nature or another. Workers required to wear a uniform may include retail workers, bank and post-office workers, public-security and health-care workers, blue-collar employees, personal trainers in h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beam Pattern
In the field of antenna design the term radiation pattern (or antenna pattern or far-field pattern) refers to the ''directional'' (angular) dependence of the strength of the radio waves from the antenna or other source.Constantine A. Balanis: "Antenna Theory, Analysis and Design", John Wiley & Sons, Inc., 2nd ed. 1982 David K Cheng: "Field and Wave Electromagnetics", Addison-Wesley Publishing Company Inc., Edition 2, 1998. Edward C. Jordan & Keith G. Balmain; "Electromagnetic Waves and Radiating Systems" (2nd ed. 1968) Prentice-Hall. Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern may also be used as a synonym for the near-field pattern or Fresnel pattern.Institute of Electrical and Electronics Engineers, "The IEEE standard dictionary of electrical and electronics terms"; 6th ed. New York, N.Y., Institute of Electrical and Electronics Engineers, c1997. IEEE Std 100-1996. d. Standards Coordinating Committee 10, Terms and Def ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Array Factor
An array is simply a group of objects, and the array factor is a measure of how much a specific characteristic changes because of the grouping. This phenomenon is observed when antennas are grouped together. The radiation (or reception) pattern of the antenna group is considerably different from that of a single antenna. This is due to the constructive and destructive interference properties of radio waves. A well designed antenna array, allows the broadcast power to be directed to where it is needed most. These antenna arrays are typically one dimensional, as seen on collinear dipole arrays, or two dimensional as on military phased arrays. In order to simplify the mathematics, a number of assumptions are typically made: 1. all radiators are equal in every respect 2. all radiators are uniformly spaced 3. the signal phase shift between radiators is constant. The array factor AF is the complex-valued far-field radiation pattern obtained for an array of N isotropic radiat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dot Product
In mathematics, the dot product or scalar productThe term ''scalar product'' means literally "product with a Scalar (mathematics), scalar as a result". It is also used for other symmetric bilinear forms, for example in a pseudo-Euclidean space. Not to be confused with scalar multiplication. is an algebraic operation that takes two equal-length sequences of numbers (usually coordinate vectors), and returns a single number. In Euclidean geometry, the dot product of the Cartesian coordinates of two Euclidean vector, vectors is widely used. It is often called the inner product (or rarely the projection product) of Euclidean space, even though it is not the only inner product that can be defined on Euclidean space (see ''Inner product space'' for more). It should not be confused with the cross product. Algebraically, the dot product is the sum of the Product (mathematics), products of the corresponding entries of the two sequences of numbers. Geometrically, it is the product of the Euc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steering Vector
Steering is the control of the direction of motion or the components that enable its control. Steering is achieved through various arrangements, among them ailerons for airplanes, rudders for boats, cylic tilting of rotors for helicopters, and many more. Aircraft Aircraft flight control systems are normally steered when airborne by the use of ailerons, spoileron, or both to bank the aircraft into a turn; although the rudder can also be used to turn the aircraft, it is usually used to minimize adverse yaw, rather than as a means to directly cause the turn. On the ground, aircraft are generally steered at low speeds by turning the nosewheel or tailwheel (using a tiller or the rudder pedals) or through differential braking, and by the rudder at high speeds. Missiles, airships and large hovercraft are usually steered by a rudder, thrust vectoring, or both. Small sport hovercraft have similar rudders, but steer mostly by the pilot shifting their weight from side to side and unba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Manifold Vector
In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a neighborhood that is homeomorphic to an open subset of n-dimensional Euclidean space. One-dimensional manifolds include lines and circles, but not self-crossing curves such as a figure 8. Two-dimensional manifolds are also called surfaces. Examples include the plane, the sphere, and the torus, and also the Klein bottle and real projective plane. The concept of a manifold is central to many parts of geometry and modern mathematical physics because it allows complicated structures to be described in terms of well-understood topological properties of simpler spaces. Manifolds naturally arise as solution sets of systems of equations and as graphs of functions. The concept has applications in computer-graphics given the need to associate pi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
L'Hôpital's Rule
L'Hôpital's rule (, ), also known as Bernoulli's rule, is a mathematical theorem that allows evaluating limits of indeterminate forms using derivatives. Application (or repeated application) of the rule often converts an indeterminate form to an expression that can be easily evaluated by substitution. The rule is named after the 17th-century French mathematician Guillaume de l'Hôpital. Although the rule is often attributed to de l'Hôpital, the theorem was first introduced to him in 1694 by the Swiss mathematician Johann Bernoulli. L'Hôpital's rule states that for functions and which are defined on an open interval and differentiable on I\setminus \ for a (possibly infinite) accumulation point of , if \lim \limits_f(x)=\lim \limits_g(x)=0 \text\pm\infty, and g'(x)\ne 0 for all in I\setminus \, and \lim \limits_\frac exists, then :\lim_\frac = \lim_\frac. The differentiation of the numerator and denominator often simplifies the quotient or converts it to a limit t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visible Region
The visible spectrum is the band of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' (or simply light). The optical spectrum is sometimes considered to be the same as the visible spectrum, but some authors define the term more broadly, to include the ultraviolet and infrared parts of the electromagnetic spectrum as well, known collectively as '' optical radiation''. A typical human eye will respond to wavelengths from about 380 to about 750 nanometers. In terms of frequency, this corresponds to a band in the vicinity of 400–790 terahertz. These boundaries are not sharply defined and may vary per individual. Under optimal conditions, these limits of human perception can extend to 310 nm (ultraviolet) and 1100 nm (near infrared). The spectrum does not contain all the colors that the human visual system can distinguish. '' Unsaturated colors'' such as pink, or purple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
