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Half-wave Dipole
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. 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 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 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 ground. A common example of a dipole is the "rabbit ears" television antenna found on broadcast te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Half – Wave Dipole
One half ( : halves) is the irreducible fraction resulting from dividing one by two or the fraction resulting from dividing any number by its double. Multiplication by one half is equivalent to division by two, or "halving"; conversely, division by one half is equivalent to multiplication by two, or "doubling". One half often appears in mathematical equations, recipes, measurements, etc. Half can also be said to be one part of something divided into two equal parts. For instance, the area ''S'' of a triangle is computed. :''S'' = × perpendicular height. One half also figures in the formula for calculating figurate numbers, such as triangular numbers and pentagonal numbers: : \frac and in the formula for computing magic constants for magic squares : M_2(n) = \frac \left(n^ + 1\right) The Riemann hypothesis states that every nontrivial complex root of the Riemann zeta function has a real part equal to . One half has two different decimal expansions, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antenna Gain
In electromagnetics, an antenna's gain is a key performance parameter which combines the antenna's directivity and radiation efficiency. The term ''power gain'' has been deprecated by IEEE. In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power. When no direction is specified, gain is understood to refer to the peak value of the gain, the gain in the direction of the antenna's main lobe. A plot of the gain as a function of direction is called the antenna pattern or radiation pattern. It is not to be confused with directivity, which does ''not'' take an antenna's radiation efficiency into account. Gain or 'absolute gain' is defined as "The ratio of the radiation intensity in a given direction to the radiation intensity that would be produced if ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loading Coil
A loading coil or load coil is an inductor that is inserted into an electronic circuit to increase its inductance. The term originated in the 19th century for inductors used to prevent signal distortion in long-distance telegraph transmission cables. The term is also used for inductors in antenna (radio), radio antennas, or between the antenna and its feedline, to make an electrically short antenna resonance, resonant at its operating frequency. The concept of loading coils was discovered by Oliver Heaviside in studying the problem of slow signalling speed of the first transatlantic telegraph cable in the 1860s. He concluded additional inductance was required to prevent amplitude and time delay distortion of the transmitted signal. The mathematical condition for distortion-free transmission is known as the Heaviside condition. Previous telegraph lines were overland or shorter and hence had less delay, and the need for extra inductance was not as great. Submarine communications ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Capacitive Reactance
In electrical circuits, reactance is the opposition presented to alternating current by inductance or capacitance. Greater reactance gives smaller current for the same applied voltage. Reactance is similar to resistance in this respect, but does not lead to dissipation of electrical energy as heat; instead, energy is momentarily stored in the reactance, and a quarter-cycle later returned to the circuit. Reactance is used to compute amplitude and phase changes of sinusoidal alternating current going through a circuit element. Like resistance, reactance is measured in ohms, with positive values indicating ''inductive'' reactance and negative indicating ''capacitive'' reactance. It is denoted by the symbol X. An ideal resistor has zero reactance, whereas ideal inductors and capacitors have zero resistance. As frequency increases, inductive reactance increases and capacitive reactance decreases. Comparison to resistance Reactance is similar to resistance in that larger reactan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hertzian Dipole
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. 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 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 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 ground. A common example of a dipole is the "rabbit ears" television antenna found on broadcast te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Guglielmo Marconi
Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi (; 25 April 187420 July 1937) was an Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system. This led to Marconi being credited as the inventor of radio, and he shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun "in recognition of their contributions to the development of wireless telegraphy".Guglielmo Marconi: The Nobel Prize in Physics 1909 . nobelprize.org Marconi was also an entrepreneur, businessman, and founder of The Wireless Telegraph & Signal Company in the |
Radio Wave
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (shorter than a grain of rice); at 30 Hz the corresponding wavelength is (longer than the radius of the Earth). Like all electromagnetic waves, radio waves in a vacuum travel at the speed of light, and in the Earth's atmosphere at a close, but slightly lower speed. Radio waves are generated by charged particles undergoing acceleration, such as time-varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects, and are part of the blackbody radiation emitted by all warm objects. Radio waves are generated artificially by an electronic device called a transmitter, which is connected to an antenna which radiates the waves. They are received by another antenna connected to a radio receiver, w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heinrich Hertz
Heinrich Rudolf Hertz ( ; ; 22 February 1857 – 1 January 1894) was a German physicist who first conclusively proved the existence of the electromagnetic waves predicted by James Clerk Maxwell's equations of electromagnetism. The unit of frequency, cycle per second, was named the "hertz" in his honor.IEC History . Iec.ch. Biography Heinrich Rudolf Hertz was born in 1857 in , then a sovereign state of the German Confederation, into a prosperous and cultured Hanseatic family. His father wa ...[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corner Reflector Antenna
A corner reflector antenna is a type of directional antenna used at VHF and UHF frequencies. It was invented by John D. Kraus in 1938.Kraus, John D., US patent 2270314 Corner reflector antenna filed January 31, 1940; granted January 20, 1942. It consists of a dipole driven element mounted in front of two flat rectangular reflecting screens joined at an angle, usually 90°. Corner reflector antennas have moderate gain of 10–15 dB, high front-to-back ratio of 20–30 dB, and wide bandwidth. Corner reflector antennas are widely used for UHF television receiving antennas, point-to-point communication links and data links for wireless WANs, and amateur radio antennas on the 144, 420, and 1296 MHz bands. They radiate linearly polarized radio waves and can be mounted for either horizontal or vertical polarization. The corner reflector ''antenna'' should not be confused with a '' corner reflector'', a passive device used to reflect radio waves back toward th ... [...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 are used ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Horn Antenna
A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are used as feed antennas (called feed horns) for larger antenna structures such as parabolic antennas, as standard calibration antennas to measure the gain of other antennas, and as directive antennas for such devices as radar guns, automatic door openers, and microwave radiometers. Their advantages are moderate directivity, low standing wave ratio (SWR), broad bandwidth, and simple construction and adjustment. One of the first horn antennas was constructed in 1897 by Bengali-Indian radio researcher Jagadish Chandra Bose in his pioneering experiments with microwaves. reprinted in The modern horn antenna was invented independently in 1938 by Wilmer Barrow and G. C. Southworth The development of radar in World War 2 stimul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Directional Antenna
A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced interference from unwanted sources. Directional antennas provide increased performance over dipole antennas—or omnidirectional antennas in general—when greater concentration of radiation in a certain direction is desired. A high-gain antenna (HGA) is a directional antenna with a focused, narrow radiowave beam width, permitting more precise targeting of the radio signals. Most commonly referred to during space missions, these antennas are also in use all over Earth, most successfully in flat, open areas where there are no mountains to disrupt radiowaves. By contrast, a low-gain antenna (LGA) is an omnidirectional antenna with a broad radiowave beam width, that allows the signal to propagate reasonably well even in mountainous regions and is thus more reliable regardless of terrain. Low-gain antennas are often used ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
