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 thick/thin dielectric material would change electric field in reactive near field?
What would happen to an antenna, tested with magnetic probes in the reactive near field, when the distance between probes and antenna was filled in by:
1) Thin Air and Thick Dielectric (Probes - 1mm ...
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How does an antenna work?
I'm looking for a model of an antenna that would explain how it works an in particular where the values of impedance like 36.5 ohms come from. I've tried looking but everything i found was overly ...
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Dipole Antenna: Electromagnetic Wave
I have read about wave propagation and dipole antennas here. I do not understand how a single electromagnetic wave (i.e. the electric field in particular - I can come up with the magnetic field later) ...
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Wave Propagation: Dipole Antenna
I was watching the following video here. This video explains the following image below represents an electric field generated from a dipole antenna. How does a single wave of electromagnetic radiation ...
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Shortening a Dipole Antenna: What happens?
Say we have an AC voltage load that is connected to a transmitter dipole, radio antenna. The antenna has a length of $L =\frac{\lambda}{2}$ where $\lambda$ is the wavelength of the electromagnetic ...
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Which theory/model explains electrons movement inside a transmitting antenna? [closed]
I have an understanding of electrical circuits, however I am very interested to know more about electromagnetic waves radiation.
In particular I want to know how an oscillating voltage causes the ...
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Is the electric flux from the antenna able to exist without connecting electric charge?
https://en.wikipedia.org/wiki/Radio_wave#/media/File:Dipole_xmting_antenna_animation_4_408x318x150ms.gif
According to above figure, the electric flux is in the close loop state like a balloon and is ...
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How strength of RF coupling depend on the antenna material?
If we place different materials in the microwave owen, they will get hot at different speeds. For instance meals get hot really fast. What material property decides on the strength of the coupling? ...
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From the physics standpoint, how should I align a USB Internet stick relative to the nearest cell tower in order to have the best signal? [closed]
I use this USB Internet stick:
(Huawei E3372h-153)
To connect to the Internet, I simply insert a SIM card into this stick and then insert the stick into a USB port of my laptop.
Based on my ...
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Why do parabolic antennas need to be the same width as their wavelength?
I am reading the wikipedia page for parabolic antennas, and have a question about the below quote:
In order to achieve narrow beamwidths, the parabolic reflector must be much larger than the ...
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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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What's the relative phase between current, voltage and electric field in a receiving dipole antenna?
To help keep the question simple, please assume a half wavelength dipole at resonance such as in the image below:
I have been thinking about this problem using the analogy of a harmonic oscillator: ...
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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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Wireless Power Transfer Modelling
I am trying to develop an analytical model for RF wireless power transfer from an external antenna to an implant antenna, embedded inside layers of lossy tissue.
The external antenna will be ...
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Electric field of dipole antenna
I have seen that the electric field of a dipole antenna detaches and propagates.
For a section of the detached electric field, will the antenna experience recoil if the detached field moves a charged ...
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Do single-sided radiators exist?
Every single-sided antenna I have looked basically radiates in all directions but has some type of material to reflect the radiated wave to create nulls.
I'm wondering if it's possible to construct a ...
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What is the explanation that the same material could receives and reflects EM wave signal while another absorbs?
Here is B-2 Spirit, a stealth bomber by Northrop Grumman. Another one is a depiction of a parabolic dish antenna receiver. As we knew, the B-2 is a stealth aircraft, which is not reflects the received ...
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Mathematical Modelling of Wireless Power Transfer
I am trying to understand the interaction between a transmitting antenna with a certain transmitting power (denoted PTX in the diagram) and how the radiation pattern of the TX antenna is affected by a ...
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Closed electric field lines around an antenna
Why do the field lines radiated from an antenna form closed loop after detachment?
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What's the formula of SNR (Signal to Noise Ratio) to dipole antenna array (eg, LOFAR) look like?
It was wellknown that the SNR of single dish telescope reads
$$s/n=\frac{P_s}{P_n}=\frac{P_{s}}{T_n}\sqrt{\frac{t}{B}},$$
where $P_s$ is the collected power, $T_n$ the noise temperature, $t$ the ...
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Friis Transmission Equation and Wavelength dependence
The "modern" form of the Friis Transmission Equation states that :
$$\frac{P_r}{P_t} = G_t G_r \left( \frac{\lambda}{4 \pi d} \right)^2$$ where $G_t$, $G_r$ are unitless antenna gains, $\...
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Can a thermal radiating surface be replaced by an equivalent antenna with proper current distribution?
Thermal radiation is EM waves generated by electrons movements due to a non-zero absolute temperature. Given a certain material with such an emission at temperature T, is it possible to see it as an ...
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Can Stern-Gerlach spin alignment be seen as a result of EM radiation of precessing magnetic dipole?
Stern-Gerlach experiment is often seen as idealization of measurement. Using strong magnetic field, it makes magnetic dipoles (of e.g. atoms) align in parallel or anti-parallel way. Additionally, ...
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Interferometry maximum wavelength for a set of baseline lengths
I am trying to understand phase ambiguity resolution for interferometry. Unfortunately, all I have are old power points and not really any notes or textbooks on the subject.
I have found in a power ...
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Photon, EM wave
I have been told that an EM wave generate from an acceleration of a charged particle
As the wave propagates away from the charge the field strength of the charge gets weaker, so does the field ...
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Deforming LC circuit into dipole antenna
I once learned in school, and as far as I know this is also a common thing in many introductory physics books, that a parallel LC circuit can be "bent open" into a dipole antenna, like this:
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How is the power per unit angle of an antenna infinite?
In my homework the power per solid angle (or however you call it) $\dfrac{\mathrm{dP}}{\mathrm{d\Omega}}$ of an $\texttt{antenna}$
$\texttt{antenna:}$ $\textsf{just a wire of length L in z-direction ...
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How determine the angle theta if short dipole is polarized along different vectors?
i am trying to understand the solution: (i have attached q & solution key)
see part d,e,f how do we visualize rotation for gain function given different vector direction of polarization (i.e. in d,...
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Does a radio receiver "collapse" a radio wave function?
Does a radio receiver "collapse" a wave function when listening to a radio broadcast generated via a transmitting antenna?
Background:
There has been much discussion on this forum (here) ...
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Why is a receiving antenna optimal at $\frac{\lambda}{2}$, mathematically?
I can understand the qualitative argument of a recieving antenna becoming resonant: An external $E$-field causes the charges to move in a conductor and bunch up, creating a voltage. If the driving $E$-...
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Exotic types of polarization
I am aware that in the classical approximation of electromagnetic waves, waves can be linearly polarized (so that the B-field oscillates in one dimension as $B=B_0\cos(\omega t)$), circularly ...
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What is the $\frac{1}{r^2} $ term in the electric field of a Hertzian dipole equations?
Taking common equation for the electric field of a Hertzian dipole from Wikipedia:
$${\displaystyle {\begin{aligned}E_{\theta }=i{\frac {\zeta _{0}I\delta \ell }{4\pi }}\left({\frac {k}{r}}-{\frac {i}{...
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Implementation Question about Thin Wire Method of Moments
I am currently trying to implement a simple 1d thin-wire method of moments code in Python in order to practice E&M and numerical methods. I am following Gibson's "The Method of Moments in ...
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How do photons induce current in an antenna?
I have done a lot of research on this topic, but I have yet to find a good explanation in plain english (I’m dumb) that answered this for me.
I know that photons have oscillating electric and magnetic ...
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Coaxial Confusion, what really are unbalanced transmission lines? [closed]
Thanks for clicking on my question.
I do not understand how an unbalanced transmission line works.
Take for instance coaxial cable which is the subject of my confusion.
This confusion arises from the ...
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Impossible VSWR reading for inductively loaded telescopic antenna
I am trying to understand how this SWR reading with an antenna analyzer is possible: https://www.youtube.com/watch?v=PeVZFD07-xY&t=231s.
For context in that video a youtuber describes how to ...
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What are the sources of electric and magnetic fields that produce lights?
Electromagnetic waves are formed as a consequence of the interference of electric and magnetic fields. I wonder where are these fields coming from that form the light? Does the fields have to be ...
