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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 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 ...
English: Graphs of the vertical radiation patterns of three monopole antennas of different lengths, mounted over a perfectly conducting ground. The antenna is assumed to be vertical. The graphs represent sections through the symmetrical omnidirectional pattern. The radial distance of the line from the origin at any elevation angle is ...
Vertical polarized VHF-UHF biconical antenna 170–1100 MHz with omnidirectional H-plane pattern. Omnidirectional radiation patterns are produced by the simplest practical antennas, monopole and dipole antennas, consisting of one or two straight rod conductors on a common axis.
Effective radiated power and effective isotropic radiated power both measure the power density a radio transmitter and antenna (or other source of electromagnetic waves) radiate in a specific direction: in the direction of maximum signal strength (the "main lobe") of its radiation pattern.
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 antenna rod and its image together act like a dipole antenna of twice the length, so a monopole over an infinite, perfectly conducting plane has a radiation pattern identical to the top half of the pattern of a vertical dipole of twice the length. [1] [70] [71] For the quarter wave monopole, the antenna acts like a half wave dipole.
A closely related antenna is the inverted-L antenna. This is similar to the T-antenna except that the vertical feeder wire, instead of being attached to the center of the horizontal topload wires, is attached at one end. The name comes from its resemblance to an inverted letter "L" (Γ).