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Due to their omnidirectional radiation pattern, vertical monopole antennas are commonly used in terrestrial radio communication systems in which the direction to the transmitter or receiver is unknown or constantly changing, [7] such as broadcasting, mobile two-way radios, and wireless devices like cellphones and Wi-fi networks, [8] [4] because they radiate equal radio power in all horizontal ...
The near field refers to places nearby the antenna conductors, or inside any polarizable media surrounding it, where the generation and emission of electromagnetic waves can be interfered with while the field lines remain electrically attached to the antenna, hence absorption of radiation in the near field by adjacent conducting objects detectably affects the loading on the signal generator ...
Isotropic gain is the ratio of the power density (signal strength in watts per square meter) received at a point far from the antenna (in the far field) in the direction of its maximum radiation (main lobe), to the power , received at the same point from a hypothetical lossless isotropic antenna, which radiates equal power in all directions ...
It is shaped like the Greek letter Π or an upside-down capital letter U, and is the loop antenna analog of a ground-mounted monopole antenna. Similar to how a vertical monopole uses its ground system to produce a "phantom" image of the rest of a dipole, the missing lower half of the half-loop is replaced by its image in the ground-plane. If ...
The far-field pattern of an antenna may be determined experimentally at an antenna range, or alternatively, the near-field pattern may be found using a near-field scanner, and the radiation pattern deduced from it by computation. [1] The far-field radiation pattern can also be calculated from the antenna shape by computer programs such as NEC.
The coaxial collinear (COCO) antenna uses transposed coaxial sections to produce in-phase half-wavelength radiators. [5] A Franklin array uses short U-shaped half-wavelength sections whose radiation cancels in the far-field to bring each half-wavelength dipole section into equal phase. Another type is the omnidirectional microstrip antenna (OMA ...
Radiation resistance is instead calculated by computing the far-field radiation pattern of the antenna, the power flux (Poynting vector) at each angle, for a given antenna current. [23] This is integrated over a sphere enclosing the antenna to give the total power P r a d {\displaystyle \ P_{\mathsf {rad}}\ } radiated by the antenna.
The vertical antenna is a monopole antenna, not balanced with respect to ground. The ground (or any large conductive surface) plays the role of the second conductor of a monopole. Since monopole antennas rely on a conductive surface, they may be mounted with a ground plane to approximate the effect of being mounted on the Earth's surface.