|
Low-gain 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 in s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cellular Repeater
A cellular repeater (also known as cell phone signal booster or cell phone signal amplifier) is a type of bi-directional amplifier used to improve cell phone reception. A cellular repeater system commonly consists of a donor antenna that receives and transmits signal from nearby cell towers, coaxial cables, a signal amplifier, and an indoor rebroadcast antenna. Common components Donor antenna A "donor antenna" is typically installed by a window or on the roof a building and used to communicate back to a nearby cell tower. A donor antenna can be any of several types, but is usually directional or omnidirectional. An omnidirectional antenna (which broadcast in all directions) is typically used for a repeater system that amplify coverage for all cellular carriers. A directional antenna is used when a particular tower or carrier needs to be isolated for improvement. The use of a highly directional antenna can help improve the donor's signal-to-noise ratio, thus improving the q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arecibo Observatory
The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science Foundation (NSF). The observatory's main instrument was the Arecibo Telescope, a spherical reflector dish built into a natural sinkhole, with a cable-mount steerable receiver and several radar transmitters for emitting signals mounted above the dish. Completed in 1963, it was the world's largest single-aperture telescope for 53 years, surpassed in July 2016 by the Five-hundred-meter Aperture Spherical Telescope (FAST) in China. Following two breaks in cables supporting the receiver platform in mid-2020, the NSF decommissioned the telescope. A partial collapse of the telescope occurred on December 1, 2020, before controlled demolition could be conducted. In 2022, the NSF announced the telescope will not be rebuilt, with an educational fa ... [...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 stimulated horn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phased Array
In antenna theory, a phased array usually means an electronically scanned array, a computer-controlled array of antennas which creates a beam of radio waves that can be electronically steered to point in different directions without moving the antennas. In a simple array antenna, the radio frequency current from the transmitter is fed to multiple individual antenna elements with the proper phase relationship so that the radio waves from the separate elements combine ( superpose) to form beams, to increase power radiated in desired directions and suppress radiation in undesired directions. 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 bea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Yagi Antenna
Yagi may refer to: Places *Yagi, Kyoto, in Japan *Yagi (Kashihara), in Nara Prefecture, Japan *Yagi-nishiguchi Station, in Kashihara, Nara, Japan *Kami-Yagi Station, a JR-West Kabe Line station located in 3-chōme, Yagi, Asaminami-ku, Hiroshima, Hiroshima Prefecture, Japan * Rikutyū-Yagi Station, a railway station on the East Japan Railway Company Hachinohe Line located in Hirono, Iwate Prefecture, Japan *Yamato-Yagi Station, a Kintetsu Corporation railway train station situated in the Nara Prefecture Other uses *Yagi (surname) *Typhoon Yagi (other) * Yagi (''Usagi Yojimbo''), a comic book character *Yagi–Uda antenna A Yagi–Uda antenna or simply Yagi antenna, is a directional antenna consisting of two or more parallel resonant antenna elements in an end-fire array; these elements are most often metal rods acting as half-wave dipoles. Yagi–Ud ..., a directional radio antenna * Yagibushi, a popular Japanese folk song and dance {{disambiguation, ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helical Antenna
A helical antenna is an antenna consisting of one or more conducting wires wound in the form of a helix. A helical antenna made of one helical wire, the most common type, is called ''monofilar'', while antennas with two or four wires in a helix are called ''bifilar'', or ''quadrifilar'', respectively. In most cases, directional helical antennas are mounted over a ground plane, while omnidirectional designs may not be. The feed line is connected between the bottom of the helix and the ground plane. Helical antennas can operate in one of two principal modes: normal or axial. In the ''normal mode'' or ''broadside'' helical antenna, the diameter and the pitch of the aerial are small compared with the wavelength. The antenna acts similarly to an electrically short dipole or monopole, equivalent to a wave vertical and the radiation pattern, similar to these antennas is omnidirectional, with maximum radiation at right angles to the helix axis. For monofilar designs the rad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotropic Radiator
An isotropic radiator is a theoretical point source of electromagnetic or sound waves which radiates the same intensity of radiation in all directions. It has no preferred direction of radiation. It radiates uniformly in all directions over a sphere centred on the source. Isotropic radiators are used as reference radiators with which other sources are compared, for example in determining the gain of antennas. A coherent isotropic radiator of electromagnetic waves is theoretically impossible, but incoherent radiators can be built. An isotropic sound radiator is possible because sound is a longitudinal wave. The unrelated term ''isotropic radiation'' refers to radiation which has the same intensity in all directions, thus an isotropic radiator does ''not'' radiate isotropic radiation. Physics In physics, an isotropic radiator is a point radiation or sound source. At a distance, the sun is an isotropic radiator of electromagnetic radiation. Antenna theory In antenna the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reciprocity (electromagnetism)
In classical electromagnetism, reciprocity refers to a variety of related theorems involving the interchange of time-harmonic electric current densities (sources) and the resulting electromagnetic fields in Maxwell's equations for time-invariant linear media under certain constraints. Reciprocity is closely related to the concept of symmetric operators from linear algebra, applied to electromagnetism. Perhaps the most common and general such theorem is Lorentz reciprocity (and its various special cases such as Rayleigh-Carson reciprocity), named after work by Hendrik Lorentz in 1896 following analogous results regarding sound by Lord Rayleigh and light by Helmholtz (Potton, 2004). Loosely, it states that the relationship between an oscillating current and the resulting electric field is unchanged if one interchanges the points where the current is placed and where the field is measured. For the specific case of an electrical network, it is sometimes phrased as the statement that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tower Array
A tower array is an arrangement of multiple radio towers which are mast radiators in a phased array. They were originally developed as ground-based tracking radars. Tower arrays can consist of free-standing or guyed towers or a mix of them. Tower arrays are used to constitute a directional antenna of a mediumwave or longwave radio station. The number of towers in a tower array can vary. In many arrays all towers have the same height, but there are also arrays of towers of different height. The arrangement can vary. For directional antennas with fixed radiation pattern, linear arrangements are preferred, while for switchable directional patterns (usually for daytime groundwave versus nighttime skywave), square arrangements are chosen. Examples Tower arrays with guyed masts * Longwave transmitter Europe 1 * Transmitter Weisskirchen * Beidweiler Longwave Transmitter * Transmitter Wachenbrunn * Transmitter Ismaning (VoA-Station) Tower arrays with free standing towers * Junglinster L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequencies
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is equal to one event per second. The period is the interval of time between events, so the period is the reciprocal of the frequency. For example, if a heart beats at a frequency of 120 times a minute (2 hertz), the period, —the interval at which the beats repeat—is half a second (60 seconds divided by 120 beats). 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. Definitions and units For cyclical phenomena such as oscillations, waves, or for examples of simple harmonic motion, the term ''frequency'' is defined as the number of cycles or vibrations per unit of time. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wavelength
In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, troughs, or zero crossings, and is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. The inverse of the wavelength is called the spatial frequency. Wavelength is commonly designated by the Greek letter ''lambda'' (λ). The term ''wavelength'' is also sometimes applied to modulated waves, and to the sinusoidal envelopes of modulated waves or waves formed by interference of several sinusoids. Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency of the wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. Wavelength depends on the medium (for example, vacuum, air, or water) that a wav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
