Search results
Results From The WOW.Com Content Network
The top shows the directive pattern of a horn antenna, the bottom shows the omnidirectional pattern of a simple vertical dipole antenna. In the field of antenna design the term radiation pattern (or antenna pattern or far-field pattern) refers to the directional (angular) dependence of the strength of the radio waves from the antenna or other ...
The antenna's feed point is at the center of the disc. It is usually fed with 50-ohm coaxial cable, with the center conductor connected to the disc, and the outer conductor to the cone. The cone: The length of the cone should be a quarter wavelength of the antenna's lowest operating frequency. [2] The cone angle is generally from 25 to 40 degrees.
The radiation pattern of a simple omnidirectional antenna, a vertical half-wave dipole antenna. In this graph the antenna is at the center of the "donut," or torus . Radial distance from the center represents the power radiated in that direction.
For radials 9 electrical degrees or less ( 1 / 40 wavelength, each, or shorter) the effect on feedpoint impedance and the current in the mast is the same as extending the height of the antenna by a length of wire equal to 99% of the total length of all the radials, up to about a dozen radials.
The gain and input impedance of the antenna is dependent on the length of the whip element, compared to a wavelength, but also on the size and shape of the ground plane used (if any). A quarter wave vertical antenna working against a perfectly conducting, infinite ground will have a gain of 5.19 dBi and a radiation resistance of about 36.8 ohms.
Antenna directivity is the ratio of maximum radiation intensity (power per unit surface) radiated by the antenna in the maximum direction divided by the intensity radiated by a hypothetical isotropic antenna radiating the same total power as that antenna. For example, a hypothetical antenna which had a radiated pattern of a hemisphere (1/2 ...
The vertical mast acts as the radiating antenna radiating the radio waves, and it's base is supported on a ceramic insulator (brown) to isolate it from the ground. The diagonal wires act as a capacitive topload, increasing the current in the mast, to increase the power radiated by the antenna. The wires also act as guy lines to support the antenna.
The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a shorted quarter-wave parallel transmission line stub. [5] [1] [6] For a transmitting antenna to operate efficiently, absorbing all the power provided by its feedline, the antenna must be impedance matched to the line; it must have a resistance equal to the feedline's characteristic impedance.