* Another reason for using the Cassegrain design is to increase the focal length of the antenna, to improve the field of view Parabolic reflectors used in dish antennas have a large curvature and short focal length, to locate the focal point near the mouth of the dish, to reduce the length of the supports required to hold the feed structure or secondary reflector.

The convex secondary reflector of the Cassegrain increases the focal length, and thus the field of view, so these antennas usually use a Cassegrain design.

However, in the case of photons, power and information transfer by virtual particles is a relatively short-range phenomenon ( existing only within a few wavelengths of the field-disturbance, which carries information or transferred power ), as for example seen in the characteristically short range of inductive and capacitative effects in the near field zone of coils and antennas.

* Much of the so-called near-field of radio antennas, where the magnetic and electric effects of the changing current in the antenna wire and the charge effects of the wire's capacitive charge may be ( and usually are ) important contributors to the total EM field close to the source, but both of which effects are dipole effects that decay with increasing distance from the antenna much more quickly than do the influence of " conventional " electromagnetic waves that are " far " from the source.

Log periodic dipole arrays, Yagi-Uda antennas, and reverberation chambers have shown to achieve much higher field strengths for the power input than a simple biconical antenna in an anechoic chamber.

In practical mathematical terms, the dominance of far-field behavior with sufficient distance from the source appears because both currents and the oscillating charge-distributions in antennas ( and other radiators ) produce dipole type field behavior.

Thus, for objects such as transmitting antennas, electrical or electronic equipment, dielectric materials, or where radiation is scattering from an object, the non-radiative ' near field ' components of electromagnetic fields dominate the EM field close to the object, while electromagnetic radiation or ' far field ' behaviors dominate at greater distances.

Antenna field regions for antennas that are equal to, or shorter than, one-half wavelength of the radiation they emit, such as the whip antenna of a citizen's band radio, or the antenna in an AM radio broadcast tower.

Some radio hams record ELF ( or even lower ) signals from very large homemade antennas, and play them back at higher speeds to catch natural fluctuations in the Earth's electromagnetic field.

* As with proximity card technology, near-field communication uses magnetic induction between two loop antennas located within each other's near field, effectively forming an air-core transformer.

Side lobe detections can be eliminated using side lobe blanking which narrows the field of view, but the additional antennas and complex circuitry impose price constraints that limit this to applications for the military, air traffic control, and weather agencies.

This method can consist of a series of antennas, towers, collectors, repeaters, or other permanently installed infrastructure to collect transmissions of meter readings from AMR capable meters and get the data to a central computer without a person in the field to collect it.

The antennas were built atop large concrete platforms -- about the size of a football field, for the detection antennas.

* Directional array refers to multiple antennas arranged such that the superposition of the electromagnetic waves produce a predictable electromagnetic field.

They involve recommendations such as the minimization of cellphone usage, the limitation of use by at-risk population ( such as children ), the adoption of cellphones and microcells with as low as reasonably practicable levels of radiation, the wider use of hands-free and earphone technologies such as Bluetooth headsets, the adoption of maximal standards of exposure, RF field intensity and distance of base stations antennas from human habitations, and so forth.

As with other low frequency antennas, the crossed field antenna is installed above a ground plane which may be the Earth.

The company did extensive studies on the existing Crossed field antennas in Egypt.

They are near field systems involving alternating magnetic fields only, and may be analyzed as poorly coupled transformer windings ; their performance criteria are dissimilar to radio antennas as discussed here.

As with all small loop antennas, loopstick antennas are largely immune to locally generated ( within the near field ) electrical noise, as they are coupled directly to the magnetic field.

`` The established pattern of relative calm in the field of race relations has continued in all areas '', reported this group headed by Harold Colee of Jacksonville and including two South Floridians, William D. Singer and John B. Turner of Miami.

Some brilliant rookies nailed them down, so that this spring just two spots, left and right field, are really up for grabs.

auto, the Sport-King, in two grades -- field and special ( less than $45 and just over $45, respectively ).

New to the field is a duplex type butyrate laminate in which the two sheets of the laminate are of different color.

After another two weeks, the first young emerge, four to eight small daughters that begin to play the role of worker bees, collecting pollen and nectar in the field and caring for the new young generation while the queen retires to a life of egg laying.

On his side of the road there were two farm hands, well back in a field, leaning against a plow.

Prior to the featured race, the stewards announced that apprentice James P. Verrone is suspended ten days for crowding horses and crossing the field sharply in two races on Wednesday.

-- Billy Gardner's line double, which just eluded the diving Minnie Minoso in left field, drove in Jim Lemon with the winning run with two out in the last of the ninth to give the Minnesota Twins a 6-5 victory over the Chicago White Sox Monday.

Phil Rossoff and two other Riverside players did not go out on the field when the fighting started.

The sum, difference, product and quotient of two algebraic numbers is again algebraic ( this fact can be demonstrated using the resultant ), and the algebraic numbers therefore form a field, sometimes denoted by A ( which may also denote the adele ring ) or < span style =" text-decoration: overline ;"> Q </ span >.

This is an example of renormalization in quantum field theory — the field theory being necessary because the number of particles changes from one to two and back again.

Alfred's military reorganisation of Wessex consisted of three elements: the building of thirty fortified and garrisoned towns ( burhs ) along the rivers and Roman roads of Wessex ; the creation of a mobile ( horsed ) field force, consisting of his nobles and their warrior retainers, which was divided into two contingents, one of which was always in the field ; and the enhancement of Wessex's seapower through the addition of larger ships to the existing royal fleet.

The initial two categories here were devised by early neurologists working in the field, namely Paul Broca and Carl Wernicke.

Afghans with two captured artillery field guns in Jaji, 1984.

Modern field artillery can also be split into two other categories: towed and self-propelled.

An alternating magnetic field is applied at the atomizer ( graphite furnace ) to split the absorption line into three components, the π component, which remains at the same position as the original absorption line, and two σ components, which are moved to higher and lower wavelengths, respectively ( see Zeeman Effect ).

This instrument had the advantage of a larger field of view and he was able to obtain precise positions of a large number of stars that transited close to the zenith over the course of about two years.

From 1969-1993, home field advantage alternated between the two divisions, and from 1995-1997 home field advantage was predetermined before the season.

A field goal scores two points for the shooting team if a player is touching or closer to the basket than the three-point line, and three points ( known commonly as a 3 pointer or three ) if the player is behind the three-point line.

To the south the Dutch Guards, under the command of Colonel Wertmüller, came forward with their two field guns to seize the hamlet of Franquenée.

This system was used successfully in two military projects: field test systems used to check the electronics of the Air Force General Dynamics F-111 Aardvark fighter plane and systems used to control the countdown and launch of the Army's Pershing missile.

While ideas about altruism from one field can have an impact on the other fields, the different methods and focuses of these fields always lead to different perspectives on altruism.

Because anthropology developed from so many different enterprises ( see History of Anthropology ), including but not limited to fossil-hunting, exploring, documentary film-making, paleontology, primatology, antiquity dealings and curatorship, philology, etymology, genetics, regional analysis, ethnology, history, philosophy, and religious studies, it is difficult to characterize the entire field in a brief article, although attempts to write histories of the entire field have been made.

Biological anthropologists are interested in both human variation and in the possibility of human universals ( behaviors, ideas or concepts shared by virtually all human cultures ) They use many different methods of study, but modern population genetics, participant observation and other techniques often take anthropologists " into the field ," which means traveling to a community in its own setting, to do something called " fieldwork.

In Greek culture each of the nine Muses oversaw a different field of human creation:

The ANFC ran the Championship of Australia, the first national club competition, which commenced in 1888 and saw clubs from different states compete on an even playing field.

First, the star's strong magnetic field separating different elements in the star's hydrogen ' fuel '.

Possible solutions to the cross pollination problem are to plant a wider refuge field or plant varieties of corn that bloom at different times than the Bt fields do.

This is different from other field theories like electromagnetism, which do not have any friction or resistivity at the microscopic level, because they are time-reversible.

Crystallization is a complex and extensively-studied field, because depending on the conditions, a single fluid can solidify into many different possible forms.

If not " true " crannogs, small occupied islets ( often at least partially artificial in nature ) may be referred to as island duns, although rather confusingly, 22 islet-based sites are classified as ' proper ' crannogs due to the different interpretations of the inspectors or excavators who drew up field reports Canmore search for crannog in the Western Isles Hebridean island dwellings or crannogs were commonly built on both natural and artificial islets, usually reached by means of a stone causeway.

The concept that all the different areas of research are studying one real, existing universe is an apparent explanation of why scientific knowledge determined in one field of inquiry has often helped in understanding other fields.

The active regions involve all the phenomena directly linked to the magnetic field, which occur at different heights on the Sun's surface: sunspots and faculae, happening in the photosphere, spicules, Hα filaments and plages in the chromosphere, prominences in the chromosphere and transition region, and flares and coronal mass ejections happening in the corona and chromosphere, but if flares are very violent can perturb also the photosphere and generate a Moreton wave, as described by Uchida.

The interconnections of active regions are arcs connecting zones of opposite magnetic field, in different active regions.

If the next time the orbit loops around phase space in a different way, then it is impossible to rectify the vector field in the whole series of patches.

Both of these processes for producing electric and magnetic EMR fields have a different dependence on distance than do near-field dipole electric and magnetic fields, and that is why the EMR type of EM field becomes dominant in power “ far ” from sources.

The term “ far from sources ” refers to how far from the source ( moving at the speed of light ) any portion of the outward-moving EM field is located, by the time that source currents are changed by the varying source potential, and the source has therefore begun to generate an outwardly moving EM field of a different phase.

Stored energy is created whenever a particle has been moved through a field it interacts with ( requiring a force to do so ), but the energy to accomplish this is stored as a new position of the particles in the field — a configuration that must be " held " or fixed by a different type of force ( otherwise, the new configuration would resolve itself by the field pushing or pulling the particle back toward its previous position ).

It also gives rise to quantum optics, which is different from quantum electrodynamics in that the matter itself is modelled using quantum mechanics rather than quantum field theory.