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LPDA
A log-periodic antenna (LP), also known as a log-periodic array or log-periodic aerial, is a multi-element, directional antenna designed to operate over a wide band of frequencies. It was invented by John Dunlavy in 1952. The most common form of log-periodic antenna is the log-periodic dipole array or LPDA, The LPDA consists of a number of half-wave dipole driven elements of gradually increasing length, each consisting of a pair of metal rods. The dipoles are mounted close together in a line, connected in parallel to the feedline with alternating phase. Electrically, it simulates a series of two- or three-element Yagi–Uda antennas connected together, each set tuned to a different frequency. LPDA antennas look somewhat similar to Yagi antennas, in that they both consist of dipole rod elements mounted in a line along a support boom, but they work in very different ways. Adding elements to a Yagi increases its directionality, or gain, while adding elements to an LPDA increases ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-complementary Antenna
The self-complementary antenna (SCA) is a basic antenna for extremely broadband practical antennas.D. E. Isbell, "Log-periodic dipole arrays" ''IRE Trans. Antennas Propag.'', vol. AP-8, pp.260-267, May 1960.Y. Mushiake, Log-periodic structure provides no broad-band property for antennas. ''J. IECE Japan'', 82, No 5, pp. 510-511, May 1999. (in Japanese) This antennaS. Uda, and Y. Mushiake, "The input impedances of slit antennas," ''Tech. Rep. of Tohoku Univ.'', 14, 1, September 1949. pp. 46-59. is an arbitrarily shaped antenna which is constituted with a half of an infinitely extended planar-sheet conductor such that the shape of its complementary structure is exactly identical, or "self-complementary" with that of the original structure with two terminals for the simplest case. The self-complementary antenna has constant input impedanceY. Mushiake, "The input impedances of slit antennas," ''J. IEE Japan'', 69, 3, March 1949. pp. 87-88. (in Japanese) independent of the source frequ ... [...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] |
Parasitic Element
In an antenna array made of multiple conductive elements (typically metal rods), a driven element or active element (also called driven radiator or active radiator) is electrically connected to the receiver or transmitter while a parasitic element (or passive radiator) is not. Driven elements In a multielement antenna array (such as a Yagi–Uda antenna), the driven element or active element is the element in the antenna (typically a metal rod) which is electrically connected to the receiver or transmitter. In a transmitting antenna it is ''driven'' or ''excited'' by the radio frequency current from the transmitter, and is the source of the radio waves. In a receiving antenna it collects the incoming radio waves for reception, and converts them to tiny oscillating electric currents, which are applied to the receiver. Multielement antennas like the Yagi typically consist of a driven element, connected to the receiver or transmitter through a feed line, and a number of o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Television Antenna
A television antenna, also called a television aerial (in British English), is an antenna specifically designed for use with a television receiver (TV) to receive terrestrial over-the-air (OTA) broadcast television signals from a television station. Terrestrial television is broadcast on frequencies from about 47 to 250 MHz in the very high frequency (VHF) band, and 470 to 960 MHz in the ultra high frequency (UHF) band in different countries. Television antennas are manufactured in two different types: ''indoor'' and ''outdoor'' antennas. Indoor antennas are designed to be located on top of or next to the television set, but are ideally placed near a window in a room and as high up as possible for the best reception. The most common types of indoor antennas are the dipole ("rabbit ears"), which work best for VHF channels, and loop antennas, which work best for UHF. Outdoor antennas on the other hand are designed to be mounted on a mast on top of the owner's house ... [...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] |
Driven Element
In an antenna array made of multiple Electrical conductivity, conductive elements (typically metal rods), a driven element or active element (also called driven radiator or active radiator) is electrically connected to the radio receiver, receiver or transmitter while a parasitic element (or passive radiator) is not. Driven elements In a multielement antenna array (such as a Yagi–Uda antenna), the driven element or active element is the element in the antenna (typically a metal rod) which is electrically connected to the radio receiver, receiver or transmitter. In a transmitting antenna it is ''driven'' or ''excited'' by the radio frequency current from the transmitter, and is the source of the radio waves. In a receiving antenna it collects the incoming radio waves for reception, and converts them to tiny oscillating electric currents, which are applied to the radio receiver, receiver. Multielement antennas like the Yagi typically consist of a driven element, connected ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency Independent Antennas
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light. The interval of time between events is called the period. It is the reciprocal of the frequency. For example, if a heart beats at a frequency of 120 times per minute (2 hertz), its period is one half of a second. Special definitions of frequency are used in certain contexts, such as the angular frequency in rotational or cyclical properties, when the rate of angular progress is measured. Spatial frequency is defined for properties that vary or cccur repeatedly in geometry or space. The unit of measurement of frequency in the International System of Units (SI) is the hertz, having the symbol Hz. Definitions and units For cyclical phenomena such as oscillations, waves, or for examples o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spiral Antenna
A spiral antenna is a type of radio frequency antenna shaped as a spiral, first described in 1956. ''Archimedean spiral antennas'' are the most popular, while ''logarithmic spiral antennas'' are independent of frequency: the driving point impedance, radiation pattern and polarization of such antennas remain unchanged over a large bandwidth. Spiral antennas are inherently circularly polarized with low gain; antenna arrays can be used to increase the gain. Spiral antennas are reduced in size with its windings making it an extremely small structure. Lossy cavities are usually placed at the back to eliminate back lobes, because a unidirectional pattern is usually preferred in such antennas. Spiral antennas are classified into different configurations: Archimedean spiral, logarithmic spiral, square spiral, etc. Principle In general, antennas may operate in three different modes: traveling wave, fast wave, and leaky wave. Spiral antennas use all three. The traveling wave, formed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves), phase'' on the wave, such as two adjacent crests, troughs, or zero crossings. Wavelength is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. The multiplicative inverse, inverse of the wavelength is called the ''spatial frequency''. Wavelength is commonly designated by the Greek letter lambda (''λ''). For a modulated wave, ''wavelength'' may refer to the carrier wavelength of the signal. The term ''wavelength'' may also apply to the repeating envelope (mathematics), envelope of modulated waves or waves formed by Interference (wave propagation), interference of several sinusoids. Assuming a sinusoidal wave moving at a fixed phase velocity, wave speed, wavelength is inversely proportion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Self-similarity
In mathematics, a self-similar object is exactly or approximately similar to a part of itself (i.e., the whole has the same shape as one or more of the parts). Many objects in the real world, such as coastlines, are statistically self-similar: parts of them show the same statistical properties at many scales. Self-similarity is a typical property of fractals. Scale invariance is an exact form of self-similarity where at any magnification there is a smaller piece of the object that is similar to the whole. For instance, a side of the Koch snowflake is both symmetrical and scale-invariant; it can be continually magnified 3x without changing shape. The non-trivial similarity evident in fractals is distinguished by their fine structure, or detail on arbitrarily small scales. As a counterexample, whereas any portion of a straight line may resemble the whole, further detail is not revealed. Peitgen ''et al.'' explain the concept as such: Since mathematically, a fractal may sho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Impedance Of Free Space
In electromagnetism, the impedance of free space, , is a physical constant relating the magnitudes of the electric and magnetic fields of electromagnetic radiation travelling through free space. That is, Z_0 = \frac, where is the electric field strength, and is the magnetic field strength. Its presently accepted value is : , where Ω is the ohm, the SI unit of electrical resistance. The impedance of free space (that is, the wave impedance of a plane wave in free space) is equal to the product of the vacuum permeability and the speed of light in vacuum . Before 2019, the values of both these constants were taken to be exact (they were given in the definitions of the ampere and the metre respectively), and the value of the impedance of free space was therefore likewise taken to be exact. However, with the revision of the SI that came into force on 20 May 2019, the impedance of free space as expressed with an SI unit is subject to experimental measurement because only t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UHF Television Broadcasting
UHF television broadcasting is the use of ultra high frequency (UHF) radio for Terrestrial television, over-the-air transmission of television signals. UHF frequencies are used for both analog television, analog and digital television broadcasts. UHF channels are typically given higher channel numbers, like the US arrangement with Very high frequency, VHF channels (initially) 1 to 13, and UHF channels (initially) numbered 14 to 83. Compared with an equivalent VHF television transmitter, to cover the same geographic area with a UHF transmitter requires a higher effective radiated power, implying a more powerful transmitter or a more complex antenna. However, the additional channels allow more broadcasters in a given region without causing objectionable mutual interference. UHF broadcasting became possible due to the introduction of new high-frequency vacuum tubes developed by Philips immediately prior to the opening of World War II. These were used in experimental television re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
