It's not necessarily like an electromagnet, but an antenna can either send or receive electromagnetic radiation (photons).Does a antenna just send out photons or is it like a electromagnet and send/recieve them?
At the level of an RF (below 10's of GHz) antenna the distinction is meaningless. There are huge (zillions ) numbers of photon-electron interactions so accounting for photon exchanges makes no scientific sense because we have a macroscopic scale where classical EM RF theory works perfectly well.I'm trying to understand the exchange of photons in a general accounting sence. Does a antenna just send out photons or is it like a electromagnet and send/recieve them?
Thanks for your expertise!
That, of course, is referring to the near-field radiation from the antenna, not the far-field radiated electromagnetic wave.It is important to note that the antenna Electric field radiates, or travels, much farther than the simultaneous Magnetic field.
... Apparently then, the 1/R attenuation of the Electric field would be related to the so-called ground wave Electric field, emanating from the antenna.That, of course, is referring to the near-field radiation from the antenna, not the far-field radiated electromagnetic wave.
Ground (hugging) RF waves can be detected using the magnetic field component of the propagating EM wave.Radio coverage predictions are almost invariably made in terms of electric field strengths. This also applies for LF and MF broadcasting even though most domestic receivers incorporate magnetic field antennas in the form of ferrite rods
The Earth has a magnetic field I can measure. I know of experiments that measured flux line that went out in space 1000s of miles and came back to earth. (traveled from pole to pole) Those fields were measured near the poles.The Magnetic field is strictly local,
... Say you have a dipole antenna, in a horizontal orientation, then there will be some part of the E field that will radiate at a vertical angle, such that it can reflect off the ionosphere and achieve a greater communication distance. The fraction of the antenna E field which is directed downward towards the ground will possess a greatly attenuated communication distance. ... And the magnetic field generated by the antenna will not be able to achieve any long distance communication, in a practical sense.RE: drc ""intensity of the Electric field attenuates as the distance R from the antenna, decreases as 1/R, while the Magnetic field decreases as 1/R^2."" Yes, however measuring around the large transmitter towers mostly dominates the magnetic component what is most prone to exceed the health standards, but it fast decrease in about kilometer distance, whilst electric component diminishes in about 100 kilometers to practical zero. The same thing around the 50 Hz 110 kV power lines - in the near 50 to 100 meter zone dominates the H-field what most probable will exceed the residential health normative while E-field is exceeded just straight beyound the wires, but something of it may be read even after 300 meters where H-field is sure zero.
That's the case of near-field reactive fields having usually very limited range because they are usually expressed as separate components of EM energy.... Say you have a dipole antenna, in a horizontal orientation, then there will be some part of the E field that will radiate at a vertical angle, such that it can reflect off the ionosphere and achieve a greater communication distance. The fraction of the antenna E field which is directed downward towards the ground will possess a greatly attenuated communication distance. ... And the magnetic field generated by the antenna will not be able to achieve any long distance communication, in a practical sense.
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In the far field, the electric field E and the magnetic field H are orthogonal and the free space impedance is equal to 377 Ω. ... In the far field, the measurement of only one quantity, E or H or S, is enough. The other quantities can be calculated by means of equation (2.23).
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