Questions tagged [antennas]
The interfaces between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. Antennas are essential components of all radio equipment.
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How does an antenna emit photons at a specific frequency if the antenna is made up a specific metal (Al) for example?
My base assumptions...
An antenna emits energy over long distances in the form of photons.
A photon is emitted when an electron changes energy state from higher to lower levels.
A photon's "...
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Overview work on radio solitons?
I've heard about solitons in dense mediums (water), sparse mediums (acoustic) and optical fiber.
But I can't find a good overview work on solitons in radio spectrum. Something like generating EM ...
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When does Lorentz reciprocity not apply to an EM system?
I'm trying to understand the limits of when Lorentz reciprocity does and doesn't apply to a given system. I know that it only applies to linear systems, but based on a couple of examples I believe ...
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If the speed of light is a constant value and the wavelength is constant (antenna), how can one antenna transit/receive different frequencies?
The speed of light is about 300,000,000 m/s, and the wavelength is determined by the design of the antenna, how can one antenna transmit different frequencies other than just the one defined by
f = c /...
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What does an antenna actually measure? The magnitude of the electric field, or the real component of the complex phasor representation?
I'm in the process of writing a physics simulation code, involving some antenna modeling. In the process of doing so, I've realized that I'm not so confident in my understanding of what an antenna ...
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When designing antennas which speed of light should be used?
When calculating "antenna element length" should we use the speed of light in the "medium between transmitter and receiver (antenna)" or the speed of light in the "element ...
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Why does inserting a ferrite core into a loop antenna increase its radiation resistance?
I have been reading the Loop Antenna section of Antenna Theory by Constantine Balanis and trying to understand how exactly a ferrite core improves the performance of a small loop antenna. Balanis ...
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Why do the dielectric caps of parabolic antennas have a metal frame inside?
Why are the so-called radio-transparent dielectric caps covering parabolic antennas based on a metal frame, which, in theory, will work like a Faraday grid, and if it does not absorb the entire signal,...
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Impedance at Feed Point and End of Antenna
Watching this pretty great video from 1947 about antenna fundamentals. I have a question about one part of it though.
The video states that the impedance at the feed point of the antenna is 72 ohms, ...
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Antennas and Wavelength
I'm clearly missing something here, but I'm trying to grasp basics of how antennas work.
Relating it to standing waves on a string of length L, the lowest frequency possible is a wavelength of 2L, due ...
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How did a spark generate electromagnetic fields that radiate to places?
In the video and pictures below, this guy is trying to replicate Hertz's experiment to generate electromagnetic fields from a dipole antenna. How did a spark generate electromagnetic fields? I thought ...
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Two ray ground reflection model to predict antenna performance over conducting ground
I have an antenna that is placed at a certain height over conducting ground plane. If it's measured, I could imagine ripples in a farfield pattern owing to reflection from the ground. Is it correct to ...
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Single-Antenna-Single-Pass SAR interferometry
As I understand, for elevation mapping using InSAR, one typically requires an out-of-plane baseline to create the required phase difference between images to detect objects at height. This usually ...
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Do electromagnetic antennas transmit (unintentionally scatter) when they receive?
My electromagnetic waves professor said any time an electromagnetic signal is received by an antenna, a transmission also occurs.
I have not independently verified this, but I believe it is likely ...
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Antennas and relativity
Antennas work by accelerating electrons to emit EM radiation. In fact, my understanding is that any accelerating electron will emit EM radiation.
But in relativity, no frame of reference is preferred. ...
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