![]() ![]() [Side note: Sometimes you will see an antenna in a datasheet labelled as isotropic what they mean is it is isotropic in one major plane for instance aĭipole antenna has a perfectly symmetric radiation pattern in the x-y plane, or azimuth plane, and is sometimes referred to as isotropic. No perfectly isotropic antennas actually exist. The isotropic antenna is used as a common reference, even though ![]() Antenna 1 would receive 1.273 times the power ofĪn isotropic antenna. In words,Īntenna 2 receives 2.707 times more power in its peak direction than an The directivity is calculated for Antenna 2 to be 2.707 (4.32 dB).Īgain, increased directivity implies a more 'focused' or 'directional' antenna. The directivity is calculated for Antenna 1 to be 1.273 (1.05 dB). The results of the directivity calculation, using Equation : Has a higher directivity without using any mathematics. Understanding, you should think about Figure 1 and what directivity is, and determine which Using Equation, we can figure out which antenna has the higher directivity. Plots of Radiation Patterns for Antennas. Is less directional then that for antenna 2 hence we expect the directivity to be lower.įigure 1. Note that the patterns are only aįunction of the polar angle, and not a function of ![]() These radiation patterns are plotted in Figure 1. Just a measure of the peak value of radiated power divided by the average, which givesĪs an example consider two antennas, one with radiation patterns given by: Just represents the "average power radiated over all directions". This equation for directivity might look complicated,īut the numerator is the maximum value of F, and the denominator Mathematically, the formula for directivity ( D) is written as: That the peak (maximum value) of the magnitude of the radiation pattern ( F in equation ) Hence, directivity throughout this page will mean peak directivity,īecause it is rarely used in another context.]Īn antenna's normalized radiation pattern can be written as a function inĪ normalized radiation pattern is the same as a radiation pattern it is just scaled in magnitude such [Silly side note: When a directivity is specified for an antenna, what is meant is 'peak directivity'.ĭirectivity is technically a function of angle, but the angular variation is describedīy its radiation pattern. Would have effectively zero directionality, and the directivity of this type of An antenna that radiates equally in all directions 'directional' an antenna's radiation pattern is. Directivity - Directivity Previous: Field Regionsĭirectivity is a fundamental antenna parameter. ![]()
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