Relationship To Average Radiated Power
The electric field strength at a specific point can be determined from the power delivered to the transmitting antenna, its geometry and radiation resistance. Consider the case of a center-fed half-wave dipole antenna in free space . If constructed from thin conductors, the current distribution is essentially sinusoidal and the radiating electric field is given by
where is the angle between the antenna axis and the vector to the observation point, is the peak current at the feed-point, is the permittivity of free-space, is the speed of light in a vacuum, and is the distance to the antenna in meters. When the antenna is viewed broadside the electric field is maximum and given by
Solving this formula for the peak current yields
The average power to the antenna is
where is the center-fed half-wave antenna’s radiation resistance. Substituting the formula for into the one for and solving for the maximum electric field yields
Therefore, if the average power to a half-wave dipole antenna is 1 mW, then the maximum electric field at 313 m (1027 ft) is 1 mV/m (60 dBµ).
For a short dipole the current distribution is nearly triangular. In this case, the electric field and radiation resistance are
Using a procedure similar to that above, the maximum electric field for a center-fed short dipole is
Read more about this topic: Signal Strength
Famous quotes containing the words relationship to, relationship, average and/or power:
“Artists have a double relationship towards nature: they are her master and her slave at the same time. They are her slave in so far as they must work with means of this world so as to be understood; her master in so far as they subject these means to their higher goals and make them subservient to them.”
—Johann Wolfgang Von Goethe (17491832)
“Strange and predatory and truly dangerous, car thieves and muggersthey seem to jeopardize all our cherished concepts, even our self-esteem, our property rights, our powers of love, our laws and pleasures. The only relationship we seem to have with them is scorn or bewilderment, but they belong somewhere on the dark prairies of a country that is in the throes of self-discovery.”
—John Cheever (19121982)
“Since the Civil War its six states have produced fewer political ideas, as political ideas run in the Republic, than any average county in Kansas or Nebraska.”
—H.L. (Henry Lewis)
“Let us rise in the moral power of womanhood; and give utterance to the voice of outraged mercy, and insulted justice, and eternal truth, and mighty love and holy freedom.”
—Maria Weston Chapman (18061885)