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Antenna Array (electromagnetic)
An antenna array (or array antenna) is a set of multiple connected 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 receiver or transmitter by feedlines that feed the power to the elements in a specific phase relationship. The radio waves radiated by each individual antenna combine and superpose, adding together ( interfering constructively) to enhance the power radiated in desired directions, and cancelling ( 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 directions. More sophisticated array antennas may have multiple transmitter or receiver modules, each connected to a separate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eight Bay Bowtie TV Antenna
8 (eight) is the natural number following 7 and preceding 9. Etymology English ''eight'', from Old English '', æhta'', Proto-Germanic ''*ahto'' is a direct continuation of Proto-Indo-European numerals, Proto-Indo-European '':wikt:Appendix:Proto-Indo-European/oḱtṓw, *oḱtṓ(w)-'', and as such cognate with Greek and Latin , both of which stems are reflected by the English prefix :wikt:oct-, oct(o)-, as in the ordinal adjective ''octaval'' or ''octavary'', the distributive adjective is ''octonary''. The adjective ''octuple'' (Latin ) may also be used as a noun, meaning "a set of eight items"; the diminutive ''octuplet'' is mostly used to refer to eight siblings delivered in one birth. The Semitic numerals, Semitic numeral is based on a root ''*θmn-'', whence Akkadian ''smn-'', Arabic ''ṯmn-'', Hebrew ''šmn-'' etc. The Chinese numeral, written (Standard Mandarin, Mandarin: ''bā''; Cantonese language, Cantonese: ''baat''), is from Old Chinese ''*priāt-'', ultim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parabolic Antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish. The main advantage of a parabolic antenna is that it has high directivity. It functions similarly to a searchlight or flashlight reflector to direct radio waves in a narrow beam, or receive radio waves from one particular direction only. Parabolic antennas have some of the highest gains, meaning that they can produce the narrowest beamwidths, of any antenna type. In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the wavelength of the radio waves used, so parabolic antennas are used in the high frequency part of the radio spectrum, at UHF and microwave ( SHF) frequencies, at which the wavelengths are small enough that conveniently sized reflectors can be used. Parabolic antennas a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Specular Reflection
Specular reflection, or regular reflection, is the mirror-like reflection (physics), reflection of waves, such as light, from a surface. The law of reflection states that a reflected ray (optics), ray of light emerges from the reflecting surface at the same angle to the surface normal as the incident ray, but on the opposing side of the surface normal in the plane formed by the incident and reflected rays. The earliest known description of this behavior was recorded by Hero of Alexandria (Anno Domini, AD c. 10–70). Later, Ibn al-Haytham, Alhazen gave a complete statement of the law of reflection. He was first to state that the incident ray, the reflected ray, and the normal to the surface all lie in a same plane perpendicular to reflecting plane. Specular reflection may be contrasted with diffuse reflection, in which light is scattered away from the surface in a range of directions. Law of reflection When light encounters a boundary of a material, it is affected by the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High Gain Antenna
A directional antenna or beam antenna is an antenna that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio wave Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...s in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only. This can increase the power transmitted to receivers in that direction, or reduce Interference (communication), interference from unwanted sources. This contrasts with omnidirectional antennas such as dipole antennas which radiate radio waves over a wide angle, or receive from a wide angle. The extent to which an antenna's angular distribution of radiated power, its radiation pattern, is concentra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Directional Antenna
A directional antenna or beam antenna is an antenna that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain direction is desired, or in receiving antennas receive radio waves from one specific direction only. This can increase the power transmitted to receivers in that direction, or reduce interference from unwanted sources. This contrasts with omnidirectional antennas such as dipole antennas which radiate radio waves over a wide angle, or receive from a wide angle. The extent to which an antenna's angular distribution of radiated power, its radiation pattern, is concentrated in one direction is measured by a parameter called antenna gain. A high-gain antenna (HGA) is a directional antenna with a focused, narrow beam width, permitting more precise targeting of the radio signals. Most commonly referred to during space missions, these antennas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Omnidirectional Antenna
In radio communication, an omnidirectional antenna is a class of antenna (electronics), antenna which radiates equal radio power in all directions perpendicular to an Cartesian coordinate system, axis (azimuthal directions), with power varying with angle to the axis (elevation angle), declining to zero on the axis. When graphed in three dimensions ''(see graph)'' this radiation pattern is often described as ''doughnut-shaped''. This is different from an isotropic radiator, isotropic antenna, which radiates equal power in ''all'' directions, having a ''spherical'' radiation pattern. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely used for radio broadcasting antennas, and in mobile ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Half-wave Dipole
In radio and telecommunications a dipole antenna or doublet is one of the two simplest and most widely used antenna types, types of antenna; the other is the monopole antenna, monopole. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole with a radiating structure supporting a line current so energized that the current has only one node at each far end. A dipole antenna commonly consists of two identical conductive elements such as metal wires or rods. The driving current from the transmitter is applied, or for receiving antennas the output signal to the radio receiver, receiver is taken, between the two halves of the antenna. Each side of the feedline to the transmitter or receiver is connected to one of the conductors. This contrasts with a monopole antenna, which consists of a single rod or conductor with one side of the feedline connected to it, and the other side connected to some type of g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quarter-wave Antenna
A monopole antenna is a class of antenna (radio), radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of electrical conductor, conductive surface, called a ground plane. The current from the transmitter is applied, or for receiving antennas the output signal voltage to the radio receiver, receiver is taken, between the monopole and the ground plane. One side of the feedline to the transmitter or receiver is connected to the lower end of the monopole element, and the other side is connected to the ground plane, which may be the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the current from the transmitter applied between the two halves of the antenna. The monopole antenna is related mathematically to the dipole. The vertical monopole is an omnidirectional antenna with a low antenna gain, gain of 2 - 5 decibel, dBi, and radiates most of its power in horizontal directio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angular Resolution
Angular resolution describes the ability of any image-forming device such as an Optical telescope, optical or radio telescope, a microscope, a camera, or an Human eye, eye, to distinguish small details of an object, thereby making it a major determinant of image resolution. It is used in optics applied to light waves, in antenna (radio), antenna theory applied to radio waves, and in acoustics applied to sound waves. The colloquial use of the term "resolution" sometimes causes confusion; when an optical system is said to have a high resolution or high angular resolution, it means that the perceived distance, or actual angular distance, between resolved neighboring objects is small. The value that quantifies this property, ''θ,'' which is given by the Rayleigh criterion, is low for a system with a high resolution. The closely related term spatial resolution refers to the precision of a measurement with respect to space, which is directly connected to angular resolution in imaging ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Shifter
A phase shift module is a microwave network module which provides a controllable phase shift of the RF signal. Phase shifters are used in phased arrays. Classification Active versus passive Active phase shifters provide gain, while passive phase shifters are lossy. * Active: ** Applications: active electronically scanned array (AESA), passive electronically scanned array (PESA) ** Gain: The phase shifter amplifies while phase shifting ** Noise figure (NF) ** Reciprocity: not reciprocal * Passive: ** Applications: active electronically scanned array (AESA), passive electronically scanned array (PESA) ** Loss: the phase shifter attenuates while phase shifting ** NF: NF = loss ** Reciprocity: reciprocal Analog versus digital * Analog phase shifters provide a continuously variable phase shift or time delay. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yagi–Uda Antenna
A Yagi–Uda antenna, or simply Yagi antenna, is a directional antenna consisting of two or more parallel Antenna (radio)#Resonant antennas, resonant antenna elements in an Antenna array#Types, end-fire array; these elements are most often metal rods (or discs) acting as half-wave dipoles. Yagi–Uda antennas consist of a single driven element connected to a radio transmitter or radio receiver, receiver (or both) through a transmission line, and additional ''passive radiators'' with no electrical connection, usually including one so-called ''reflector'' and any number of ''directors''. It was invented in 1926 by Shintaro Uda of Tohoku University, Tohoku Imperial University, Japan, with a lesser role played by his boss Hidetsugu Yagi. (This was the preface and notice in advance for a series of eleven papers, of the same title, by Uda, between 1926 and 1929, on the antenna. However, it seems that Uda's pre-announcement caused his invention to lose its Novelty (patent), novelty and b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
