# Questions tagged [antennas]

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### Calculating magnetic field from vector potential for half wave dipole antenna

Given the far-field vector potential... $$\vec A_{\text{ff}}(\vec r) = \left(\frac{\mu_0I}{2\pi kr}e^{-jkr}\frac{\cos\left(\frac{\pi}{2}\cos(\theta)\right)}{\sin^2(\theta)}\right)\hat z$$ I need to ...
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### How do you polar-plot the complex-valued array factor (AF) of a phased antenna array? [closed]

If a normalized array factor for an $N$-element linear antenna array (without per-element phase shifts) is calculated as $$AF = \frac{1}{N}\sum_{m=0}^{N-1} e^{jmkd\cos\theta}$$ where: $\theta$ is ...
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### Waveguide operation frequency range

Google told me the operation frequency is 125% - 190% of the cutoff frequency. But I did not find any other material for reasoning. My question: What happens if frequency was too high?
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### Strange approach to the line-fed slot antenna analysis

There is a beautiful demonstration, available in the text Robert S. Elliot, Antenna theory and Design, Wiley-IEEE Press, page 17 (Stratton-Chu solution), which shows how the electromagnetic field at ...
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### Why does an ideal antenna not absorb all incident power?

http://farside.ph.utexas.edu/teaching/em/lectures/node94.html states: So, in the optimum case half of the power absorbed by the antenna is immediately re-radiated. Clearly, an antenna which is ...
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### Help understanding the “Nyquist Criterion”

I am researching the split-step parabolic equation and its split step solution as in: Ozgun, Ozlem & Apaydin, Gokhan & Kuzuoglu, Mustafa & Sevgi, Levent. (2011). PETOOL: MATLAB-based one-...
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### I'm unable to wrap around the concept of antennas and more specifically microstrip antennas. How does a microstrip antenna which is bended work?

So, I had come to the agreement that to understand how antennas work, it is best to assume light/electromagnetic waves act like photons/particles in the presence of recieving antennas. And therefore a ...
32 views

### Loop antenna $E$ and $H$ modes without approximations as to the distance or wavelength

In Jackson's 9.14 we calculate the expressions for $E$ and $H$ of a loop antenna with current $I=I_0\cos(\omega t)$ in the $x-y$ plane in the radiation zone, where we approximate the distances to be ...
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### Magnetic field closed loop lines in an electromagnetic wave

let's consider the simplest example of electromagnetic waves: If we consider only this picture, it seems that the magnetic field lines are not closed loops, which is clearly not possible. I know it ...
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### Polarization of Patch antenna - Intuitive explanation

I was looking into the polarization of patch antennas (for GNSS use). I found this website (http://kempbros.github.io/antennas/Patch_Antenna_Generator/) which gives the geometry of the antenna ...
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### How to calculate the reflection efficiency for an antenna? [closed]

I want to calculate the reflection efficiency of a transmitting monopole antenna which is connected to a 50 ohm lossless transmission line. And I know that the input impedance of a monopole antenna is ...
24 views

### In an AC Current, if the voltage is high, does this “amplify” the radiowave emissions without changing the frequency?

Hello My question comes from my interest in antennas i suppose: I understand that antennas utilize alternating current to generate EMF Waves along a particular frequency depending on how quickly the ...
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### Converting $\frac{dB\mu A}{m}$ to $\frac{dB\mu V}{m}$? [closed]

I am trying to convert $\frac{dB\mu A}{m}$ to $\frac{dB\mu V}{m}$ So, I know that; $\frac{dB\mu V}{m}$ = $\frac{dB\mu A}{m} + 51.5$ However, I cannot find a source explains where 51.5 comes from. ...
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### Dipole oscillators question from Feynman lectures 1.28-29

I am confused by the Feynman lectures Vol1Ch28-29. In all the pictures, there is an electric dipole oscillating vertically. We're assuming the intensity is $E^2$ and that in the far r limit $E$ ...
33 views

### Derivation of the Gaussian Beam Pattern

I am currently reading this book by Mireille Levy. It says (on page 40) that the Gaussian beam pattern with half-power beamwidth $\beta$ is gien by: B(\theta)=A\text{exp}\left(-2\text{log}2\frac{\...
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### Why is the effective area of a dipole antenna receiver greater than it's actual size?

The receiving ability of a dipole antenna is much greater than what is attained when doing calculations involving a plane wave interacting with its actual size. Why is this? How can an antenna pull ...
100 views

### How do antennas work?

I know the basics about em radiation. However, I’m not in college, and I’m not a genius. I’m really looking for someone that’s willing to help explain this to me in a relatively simple way, without ...
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### Simplified model of antenna polarization loss

I need to write a very simple model to estimate the $dB$ value of the polarization loss between two antennas (in realtime). Such antennas are common (yet identical) omnidirectional dipole antennas, ...
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### Electromagnetic radiation and angular power distribution in time vs. frequency domain

So I am taking an electrodynamics course right now where we are currently learning about radiation from antennas. In our lecture, my professor had derived a formula for angular power distribution ...
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### Source of cylindrical electromagnetic waves

I have a question about waves with cylindrical wavefront. Precisely, I have read that they may be generated by a linear source, while for instance plane and spherical waves are respectively generated ...
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### Why are the electric and magnetic waves produced by an antenna in phase?

From my understanding, an antenna produces an electric field when charges are separated, and produces a magnetic field when they are flowing. However, when the magnetic field is at a maximum, the ...
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### Inverted antennas

Im trying to draw the E and H plane for radiation pattern for two-parallel-dipoles-in-out-of-phase-by-180, in other words I have two inverted anntena dipoles with same distance from each other in ...
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### Derivation of the total received field in ground reflection model

I am reading this book by J.D. Parsons. The problem concerned, is how to find the propagation model for propagation over a curved reflecting surfac, i.e.: I would like to know where is the ...
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### When does an EM wave become a photon?

Consider a small LC circuit which is oscillating at some rate. The wavelength is VERY long compared to the diameter of the inductor. (100's of meters) Beyond the radiansphere, where the EM waves are ...
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### How does a mobile patch antenna receive the correct signal in any orientation and rotation?

For instance if we take a dipole and then rotate the receiving dipole 90 degrees such that it forms a cross against the transmitting dipole, would the signal be retrieved at all? If it were rotated ...
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### Is there any factors depends for electromagnetic waves?

I am staying in hostel. One person said me that he is getting better connection with the wifi when the door is opened. I am wondering that what an electromagnetic wave can do with the door? Is there ...
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### Near-field energy transfer

If you absorb energy in the near field of the antenna, it will produce a loading effect on the source. Whereas in the far field it will not. Is there an intuitive explanation why this is true for one ...
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### How is cosmic microwave background radiation experimentally detected?

Can it be detected from the earth with a single dipole antenna or a series of such antenna forming an interferometer (with an electric circuit to filter out the noise due to radio stations and ...
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### Where does the energy go to for a charged sphere with pulsing radius?

In the question A charged sphere with pulsing radius the answer says that the charged sphere does not radiate. However, compressing a sphere of charge to a smaller radius requires work, so where does ...
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### Does the microwave generating component in a microwave operate under the same physics as an antenna radio transmitter?

Essentially does the component of a microwave which generates those microwave photons operate using an AC power supply connected to a broken circuit which causes an oscillating dipole to radiate ...
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### Basic question on Poynting flux and antennae

I am looking at a question (though my queries here are more regarding th underlying conepcts, which I don't quite understand) about a radio antenna that is polarising a conducting sphere. For ...
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Since extremely-low-frequency radio waves are used by submarines for some simple, low-transmission-rate communications, why can't those same wavelengths be used for submarine radar? It may not be ...
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### What is the current in a short linear antenna in an alternating $E$-field?

Consider a short linear wire with some low but non-zero resistance, such as a copper wire. If this wire is then placed in an alternating electric field that is oriented parallel to the wire, the field ...
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### What part of the energy applied to accelerate electrons radiate and why?

I understand that accelerated electrons will emit radiations, for example in a cyclotron or antenna. However I dont understand why some energy will sort of stay in the electrons and accelerate them, ...