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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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2 answers
84 views

Can we catch signals from a cellphone using an external device? [closed]

What if someone stole em waves from our mobile devices to listen to our conversations or get our OTP. Whatever encryptions they have they are just EM waves innit and they cannot be propagated only in ...
Newtron Malayalam's user avatar
1 vote
0 answers
42 views

Dipole antennas and the $B$ field

A dipole antenna responds to the electric component of a EM wave. Does the magnetic component of a EM wave have any effect on the performance of a receiving dipole antenna?
Rich D's user avatar
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15 votes
7 answers
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Why does the length of an antenna matter when electromagnetic waves propagate perpendicular to the antenna?

The optimum length for a dipole antenna is a multiple of half the wavelength that it is designed to receive or emit. Why is this? If an electromagnetic wave has E in the x-axis, B in the y-axis, and ...
user411769's user avatar
0 votes
1 answer
46 views

Polarization Derivation

Can how I can find the phi and theta unit vectors as described (Eq. 4a and 4b) in the following paper on antenna cross polarization? I thought the thetha and phi unit vectors were the same as those of ...
DTBolt's user avatar
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140 votes
2 answers
71k views

How many photons are received per bit transmitted from Voyager 1?

As of 2024, according to https://voyager.jpl.nasa.gov/ , Voyager 1 is around one light·day away from Earth and still in radio contact. When Voyager 1 sends messages to Earth, roughly how many photons ...
Craig Gidney's user avatar
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0 votes
2 answers
41 views

Magnetic object affected by electromagnetic wave

If a dipole antenna is strong enough, can it make a compass needle oscillate?
Simon Lin's user avatar
  • 156
1 vote
2 answers
98 views

Electromagnetic field of dipole antenna

Why do dipole antennas generate EM waves by alternating electric fields instead of alternating magnetic fields? Why don't alternating magnetic poles detach the magnetic field like how it can do so ...
Simon Lin's user avatar
  • 156
1 vote
2 answers
52 views

Minimum frequency for a dipole antenna to work

Does a dipole antenna need a minimum frequency of AC to make the electric field detach and propagate?
Simon Lin's user avatar
  • 156
1 vote
0 answers
35 views

Measure electrical fields in space with oscilloscope and wire [closed]

I have an oscilloscope with its standard probe. Combined they have 1MOhm resistance and 71pF capacitance. I attach a 50cm wire floating in space to the probe and connect the ground clip of the probe ...
Hansebenger's user avatar
0 votes
1 answer
39 views

Do small electrical field generators generate "different" electrical fields than long antennas - how to measure?

Modern electronic devices often generate electrical fields in the frequency range of 10-50kHz. I want to distingush 2 categories: Loaded onto mains (e.g. solar inverters) and then mains wiring emits ...
Hansebenger's user avatar
0 votes
1 answer
36 views

Is the current direction in transmitting and receiving dipole antenna opposite?

I googled for quite a while, but couldn't get a confirmation to this basic question. So I wonder if someone would help me out here. Suppose we have 2 dipole antennas, each of length 1 meter. One ...
syeh_106's user avatar
  • 101
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1 answer
29 views

Phasors and propagating modes in a waveguide

I'm currently studying antennas. The notes I'm following, while discussing the EM fields at the antenna feed port, make the following statement: It can be shown that a propagating mode in a ...
edoverg's user avatar
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2 votes
1 answer
45 views

How does the presence of a static electric field affect the normal operation of an antenna (if at all)?

For arguments sake lets say I have a receiving antenna that has been positioned between two large conductive plates. Are there any differences in how that antenna operates (gain, efficiency etc.) when ...
Christian's user avatar
  • 113
3 votes
0 answers
64 views

Can cell phones send message in the elevator?

From Gauss's theorem, a closed, hollow conductor shields its interior from fields due to charges outside, but does not shield its exterior from the fields due to charges placed inside it. So my ...
Yuan Fang's user avatar
  • 267
1 vote
1 answer
55 views

Understanding radiation mechanism of inset fed microstrip antenna

I have designed a simple inset-fed microstrip antenna, resonating at 2.45 GHz. The transmission line model of the antenna reduces it to two radiating slots separated by a microstrip line, and it's ...
fraghotmailcom's user avatar
0 votes
0 answers
60 views

Effective aperture as a function of Azimuth and Elevation Angle

Wikipedia says The effective aperture of an antenna is given by $$A_{\mathrm{e}}(\theta, \phi)=\eta A \cos \theta \cos \phi ,$$ where, $(\theta, \phi)$ are the azimuth and elevation angles relative to ...
wanderer's user avatar
  • 101
0 votes
1 answer
56 views

Prime operator for sinusoidal testing function in self-term approximation for Thin Wire using Method of Moments (MoM) $s_m^{'}(x_p)$?

I am implementing thin wire method of moments using W.Gibson's "Method of Moments in Electromagnetics". The approximation for self-term using piecewise sinusoidal basis function is given as ...
Ashish Magar's user avatar
1 vote
2 answers
62 views

EM wave emission from earphone wires due to varying current signal

if we listen to some audio signal on a wired earphone, then does the wire of the earphone act as a transmitter antenna to emit the audio signal as radio waves even though its strength might be ...
sab's user avatar
  • 23
0 votes
2 answers
75 views

Book Recommendation about radio frequency antennas and satellites

I have recently obtained a job in the field of radio frequency antennas and satellites, and I am interested in delving deeper into the subject. Could you recommend any books that cover these topics ...
1 vote
0 answers
54 views

How to practically generate longitudinal waves in a plasma

It can be read almost everywhere that plasma is the best convertor of transverse waves to longitudinal waves. I'm not much interested in the theory here. Rather, I would like to know how to do it in a ...
MikeTeX's user avatar
  • 487
1 vote
0 answers
19 views

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 ...
antfellow's user avatar
-1 votes
1 answer
93 views

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 ...
Jan Szwyngel's user avatar
2 votes
4 answers
167 views

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) ...
William Garske's user avatar
0 votes
1 answer
151 views

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 ...
William Garske's user avatar
0 votes
1 answer
53 views

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 ...
William Garske's user avatar
1 vote
2 answers
88 views

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 ...
MohammadAli Zeraatkar's user avatar
0 votes
0 answers
32 views

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 ...
superkappy's user avatar
0 votes
2 answers
40 views

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? ...
Mariusz's user avatar
-1 votes
2 answers
72 views

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 ...
Mitsuko's user avatar
  • 1,599
0 votes
2 answers
70 views

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 ...
Andrew Baker's user avatar
2 votes
4 answers
298 views

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 "...
Nubi78's user avatar
  • 21
0 votes
0 answers
30 views

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 ...
monday's user avatar
  • 111
1 vote
0 answers
48 views

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 ...
Christian's user avatar
  • 113
1 vote
1 answer
63 views

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 /...
epicMan123's user avatar
1 vote
0 answers
77 views

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 ...
MomentumEigenstate's user avatar
6 votes
3 answers
744 views

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 ...
Duke William's user avatar
1 vote
1 answer
321 views

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 ...
healynr's user avatar
  • 111
2 votes
1 answer
41 views

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,...
Vladimir Orlov's user avatar
6 votes
3 answers
664 views

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, ...
vigilante_fresh's user avatar
2 votes
1 answer
122 views

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 ...
vigilante_fresh's user avatar
4 votes
3 answers
2k views

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 ...
SnoopyKid's user avatar
  • 364
0 votes
1 answer
56 views

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 ...
Muhammad's user avatar
  • 169
0 votes
1 answer
45 views

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 ...
Jan Lynn's user avatar
  • 357
1 vote
2 answers
141 views

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 ...
JosephDoggie's user avatar
10 votes
1 answer
2k views

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. ...
Marc DiNino's user avatar
1 vote
0 answers
29 views

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 ...
PikaPika's user avatar
2 votes
1 answer
252 views

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 ...
Simon Lin's user avatar
  • 156
0 votes
1 answer
81 views

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 ...
FourierFlux's user avatar
1 vote
3 answers
112 views

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 ...
AirCraft Lover's user avatar
0 votes
0 answers
45 views

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 ...
PikaPika's user avatar

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