Questions tagged [antennas]

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135 views

Do wireless signals (Wifi router, radio, telephone) send their information in single "blinks" or in a continuous wave with frequency modulation or Amplitude modulation? If a radio for example needs ...
433 views

I recently tried to make a DIY foxhole radio. Althogh I made it according to the manual (140times coil rotated, ground(220V), blued razor blade, pencil core and antenna (just a steel stick about 1 ...
287 views

Waveguide horn antenna & inverse square law

With a lab waveguide / horn antenna setup similar to image (without bends), we made the following measurements. Now we thought this could be used to demonstrate the observation of the inverse square ...
101 views

Get power distribution from radiation pattern

I'm trying to get the power (or E-field, or antenna element) distribution of an antenna given the radiation pattern. I know that if you have a power distribution \$P(x)\$ along the antenna to start ...
1k views

How does a electric quadrupole oscillate?

I know that in static a electric quadrupole is made of two positive charges and two negative charges, distributed as in the following figure: What I don't understand is when it oscillates and ...
85 views

Do we get radiowaves if the antenna is a loop or a coil?

What happens if we use an antenna which is not a straight wire, i.e a loop or a coil? do we get EMR? Now, if we do, what is the difference between this loop and the primary winding of a transformer? ...
98 views

Is it not redundant for the magnetic field to induce voltage if its partner electric field hits at the receiving antenna?

If the electric field hits the receiving antenna (in form of pressure or voltage) to agitate the electrons in the receiving antenna, then what is the purpose of magnetic field then? What it serves ...
93 views

The need of modulation

Why is the transmitted signal modulated rather than sending the whole signal as a radio wave? Why is it necessary to modulate the wave? I do understand there are quite advantages of modulation but ...
4k views

How can an antenna pick up thousands of frequencies at the same time?

When we turn the tuning knob of a radio set, we pick up a different station on a different wavelength, yet the (length of the) antenna is the same: we can select any frequency at any time, we focus on ...
147 views

Is it true that the particles from the transmitting antenna (conductor) flying or travelling in the air?

Is it correct that the varying stream of electrons or photons or wavicles etc. in the transmitting antenna (i.e complex analog signal) are literally flying or traveling in air or vacuum and then get ...
21 views

How does one adapt an antennae to an electrically conductive medium?

Most antennae are deployed in earth's atmosphere which can be approximated as a vacuum. But what about an antennae for a submarine underneath the ocean? Or how about an antennae deployed in a copper ...
126 views

How do you tell whether charges oscillate in the antenna because of an electric or magnetic field?

The electrons in a receiving antenna oscillate, can we establish if they respond to an electric or a magnetic field? How can we know if there is an electric field apart from the one caused by the ...
426 views

Are sound frequencies (20-20,000Hz) included in radio waves? If not, how does sound get to our end (radio/receivers)? Is there some type of encoding going on inside those radio-frequency waves or ...
890 views

Is it a magnetic or an electric field that causes induction in the antenna?

wiki says that: The electric field (E, green arrows) of the incoming wave pushes the electrons in the rods back and forth, charging the ends alternately positive (+) and negative (ā). but ...
241 views

I have a laptop that I primarily use for music. I donāt want to have to bring my laptop to the basement every time I want to listen to music. I have bluetooth headphones and I was wondering if there ...
161 views

How to Calculate the total scattered radiation power and total radiation power.?

Let's suppose I have incident field $E^i_z$. The components of Scattered electric and magnetic field are $E^s_z$, $E^s_\phi$, $H^s_z$ and $H^s_\phi$. The electric and magnetic field components ...
180 views

Can a neutrino antenna be made one day?

I am wondering if it is theoretically possible that some kind of device/material could absorb neutrinos much better than everyday materials (preferably non-thermal absorption). This could enable a ...
352 views

How far do electrons go in an antenna?

Do you know what is the distance electrons cover in an antenna during the production of a radio wave? Does the extension of the oscillation vary with the frequency or the power of the radiation? Is ...
374 views

Is my understanding of how an antenna work correct?

So from what I know I think that the magnetic and electric fields around the antennas move away from the antennas because the vectors in the magnetic and electric field have direction and strength so ...
12k views

Why do we need an antenna of size comparable to the wavelength for surface wave transmission?

Why do we need an antenna of size comparable to the wavelength for surface wave transmission? I am unable to understand why such condition is imposed.
1k views

How do electromagnetic waves travel away from an antenna?

I have heard that in an antenna the electrons move back and forth and create an electric field which varies with time. This varying electric field in turn, creates a varying magnetic field. These two ...
52 views

Does Enamel need to be Removed From Magnet Wire for Yagi Antenna

I am using 16AWG Magnet Wire to create a 15 element Yagi Antenna for the 2.4ghz range which should theoretically give me a little over 15db gain. The magnet wire I am using has an enamel coating on it....
144 views

“Bending up” $LC$-circuit to a linear antenna mathematically

In introductory physics books one often finds a picture series leading from an $LC$-circuit to a simple linear antenna by "bending up" the $LC$-circuit, for example like this: The key difference ...
694 views

Directive gain and radiated power of an antenna

while attending a lecture on antennas, we were explained an example where it was stated that a lossless antenna with a directive gain of +6 db is going to radiate 4 mW of power if it is fed 1mW of ...
191 views

What type of polarization can we get from a dipole antenna? Circular? Linear? Elliptical? If there is a specific answer , what are the physical reasons?
148 views

Calculate EM-field or intensity field given radiation pattern

If I have a normalised radiation pattern (in dB) from an antenna, how would I go about getting the (far-field) intensity distribution? My guess would be to convert the pattern to linear gain, ...
452 views

Propagation of EM waves through antenna

I read in the book that when we apply high-frequency signal to a conductor, the signal propagates as a sinusoidal current in a conductor. But when the conductor is connected to the antenna, the signal ...
74 views

Can we see the shape of an antenna?

What I mean is the following: Is it possible from knowing the radiation pattern/frequency distribution of an antenna to calculate the geometric form of that antenna uniquely? My guess would be, that ...
173 views

Radiation of Electric Dipole - Antenna

In the theory regarding Radiation of an electric dipole, an example using an antenna is shown in which the antenna is considered as a certain length of wire with a sinusoidal current inside it. For ...
300 views

HD TV Signal reception at night

Why is on air HD TV signal reception better at night? During the daytime the reception of HD TV broadcasts is markedly lower than at night with the same antenna position. Does the sun have components ...
347 views

Why the shape of dish antenna is in parabolic shape? [closed]

All dish antenna are in the shape of parabola. Is the curve of parabola anyhow related to physical quantity of the wave of transmission? Are there different curved antennas for different waves?
52 views

Can the electrical signal in the Electromagnetic wave be rectified?

The radio waves are received through the antenna and in that case, we obtain the electric signal. Could that electric signal be rectified?
397 views

How does the energy transfer in the near field of an antenna work?

Answering the question What is the relation between electromagnetic wave and photon? I wrote The EM radiation of an antenna is measurable and it was found out that the nearfield of an antenna has ...
1k views

Average force between two parallel finite wires with AC

Imagine 2 parallel antennas (wires) of equal length (a) with a distance r between them. Both have AC currents with identical sine wave forms (equal frequencies and amplitudes) . They are also in-...
404 views

Is antenna noise temperature relevant if the physical system temperature is higher?

Assume a lossless antenna connected to a lossy cable at physical temperature 300K. If this antenna is pointed into space, the antenna noise temperature will depend on the brightness temperature of ...
4k views

How can current flow through an open wire (like a dipole antenna)?

I am trying to understand how current can flow through a dipole antenna (with length $\frac{\lambda}{2}$ or anything else) which actually is nothing more than an open wire. Could someone clarify this ...
4k views

How does a receiving antenna work?

I thought something like this would be easy to find on the web, but apparently I was wrong. Or maybe I'm using the wrong search terms. I'm imagining some kind of resonance which amplifies only a ...
1k views

What happens in near field coupling

I understand far field propagation conceptually: you have a sphere propagating outwards, and you capture only part of the surface with your antenna aperture, which you convert into an electrical ...
1k views

WIFI frequency and amplitude

My understanding of wifi and other wireless communication such as cellphones and radio is that there are essentially two components, the frequency and the amplitude. Different frequencies allow for ...
769 views

Similarities between light and other frequencies of EM waves

This may be a ridiculous question, but I'll learn something from it! Let's say there's a TV transmitter transmitting at 100kW. I can receive the station just fine 20 miles away. The antenna is 300m ...
1k views

A “figure-8” EM field created by a dipole antenna

This question pertains to the EM field of a Pulse W5017 dipole antenna. The data sheet of this antenna can be found here (which contains information regarding the radiation patterns). There are TWO ...
50 views

Can antennas work with high frequency EM waves?

Antennas usually work with FM waves, and AM waves, which mostly used in telecommunications. Information is transferred on FM, and AM waves by a transmitter transmitting information on these EM waves. ...
20 views

How can I determine if A 34 meter antenna can be used as PTA?

What are the general requirements for any antenna, e.g., one with 34 m of dish, to be used as PTA (Pulsar Timing Array) monitoring? What are the main formulae to be used? How can the TOA (time of ...
98 views

Transmission Lines and Antennas

In Transmission Lines, does the electric field exist between the two conducting wires or does it exist inside a wire, pushing the flow of electrons? And do all antennas radiate energy by spark?
233 views

Impact of antenna spacing larger than a half of wavelngth

I am building a uniform linear antenna array (ULA) of Wi-Fi to extract channel state information, or channel matrix $H$. With some literature search, as not familiar with antennas and electromagnetic ...
420 views

Antennas and the electromagnetic field

I'm an electrical engineering undergrad and have some questions about radio antennas. We've just covered the electronics and maths of radio theory once the signal has reached the receiver, I'm ...
5k views

A Formula for the Phase Difference Between the Electric and Magnetic Wave Oscillations?

A) Is there a formula for the phase difference between the electric and magnetic field oscillations, in vacuum, in an electromagnetic wave emitted from an antenna, as a function of the frequency the ...
120 views

I am trying to learn a bit about antenna theory in order to understand how Nikola Tesla may have misunderstood them. (Thank you CuriousOne for your response to my earlier question! It was helpful in ...