5
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Insight into cavity resonators
if I am correct these modes will be the same for each antenna
Not exactly. Modes themselves only depend on frequency and geometry of the cavity indeed.
However, which modes will be excited within ...
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5
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Accepted
Insight into cavity resonators
Each antenna is able to excite almost any mode, and will. The only modes that won't be excited by an antenna are those for which the antenna is at a node of the mode, a point where the standing wave ...
- 174k
4
votes
Visual understanding of EM fields within a rectangular metal container
I cannot give you a complete answer and you would need some kind of 3D electromagnetic simulator. I have used HFSS (a FEM simulator) and CST (a FDTD simulator), but both of these are extremely ...
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4
votes
Visual understanding of EM fields within a rectangular metal container
915MHz has a wavelength of about 300mm, or one foot. The container has internal dimensions of many many times this. This means the standing wave pattern, resulting from the inevitable interference, is ...
- 174k
4
votes
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Electromagnetic wave equation for GPS waves
That equation isn't derived, it describes the contents of a GPS signal that is created by the electronics in the transmitter in the GPS satellites.
The electronics create quadrature signals (I and Q) ...
- 81.4k
3
votes
How, exactly, does the 'input signal' wave(s) modify the carrier-wave of a radio signal?
The process of getting an input signal to modify the carrier-wave of a radio signal is known as modulation. The input signal is called the baseband signal or modulating signal. The combined signal is ...
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3
votes
Question on spark gap transmitter circuit
That circuit works just like old door buzzers worked -- it's just a simple relaxation oscillator.
Any oscillating electric circuit creates electromagnetic waves. The buzzer creates EM waves on a large ...
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Power calculation from E and H field
The Poynting vector \$\bf S\$ is given by
$${\bf S} = {\bf E}\times{\bf H}$$
The magnitude of the Poynting vector gives the intensity of the electromagnetic wave. That is the, the power per unit area. ...
- 134k
3
votes
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E fields and M fields in Near Field
This is mainly a problem with imprecise wording, so we'll have to pick your statements apart very carefully:
small loops with high dI/dt on a PCB tend to produce predominantly magnetic waves ...
- 100k
2
votes
Distance requirements in antenna arrays?
The minimum array size is a function of the antenna radiation pattern, the signal wavelength and the performance goals for the array. For very close spacing, the antennas may even interact with each ...
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2
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Distance requirements in antenna arrays?
can antenna arrays be decreased in size if the antenna elements themselves can be decreased in size?
No, they cannot. The antenna arrays work by constructive and destructive interference where, in ...
- 753
2
votes
Accepted
Why is a horizontal rod a full wavelength oriented radially to a broadcast antenna not the best receiving antenna
It is true that the variations in field strength propagate radially from the transmitter.
However, as your diagram shows, the fields themselves are vector fields, and the orientation of the vectors (...
- 178k
2
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Why is a horizontal rod a full wavelength oriented radially to a broadcast antenna not the best receiving antenna
The waves are not only varying as they propagate radially, but, for a vertical transmit antenna, the EM field will vary vertically as well.
That's because a vertical antenna has finite height, thus ...
- 4,851
1
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EM simulation of antenna in battery proximity using QUCS studio
You probably don't need a tutorial. You just need to be able to simulate metal. The anodes of many lithium ion cylindrical cells is connected to the anode, so you'd just have to capacitavely couple ...
- 88.8k
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What is the actual physics and reasoning for the “Ground plane” underneath a GPS patch antenna
A patch antenna looks more like a capacitor divider, with the top plate coming in from free space (incident electric field), the middle plate being the patch itself, and the ground plane being, well, ...
- 45.6k
1
vote
Accepted
Does a receiving antenna radiate the power received?
If the incoming E-M wave can induce a voltage won't it accelerate or decelerate the electrons in the wire and doesn't this acceleration cause further radiation (lets call it secondary radiation) of E-...
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1
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How do I EM-Extract a subcircuit and define a different em/drawing-layer than the original circuit in AWR?
Reposting from here since they answered the question
at the Cadence Community:
What you are asking isn’t possible although the issue isn’t due to the
extraction itself. The built-in microstrip ...
- 2,200
1
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Simulation of 2D vs 3D electromagnetic waves
I'm pretty clueless when it comes to EM simulations and viz. However, I did spend some time in biophysics and geophysics- and in general I noticed that the other scientists (the smart ones lol) would ...
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Simulation of 2D vs 3D electromagnetic waves
as @analogsystemsrf implies:
You use a 2D simulation, where you know that 2D is sufficient for the modeling of the physical system. If it is sufficient, then the results will be right.
If the ...
- 100k
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Simulation of 2D vs 3D electromagnetic waves
2D is mostly correct if you have all signals on a single layer, which you might be able to pull off with some high speed designs,
3D is when you have multiple layers, or larger components that ...
- 4,657
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Simulation of 2D vs 3D electromagnetic waves
Suppose you want to shield a PCB (assume 2_D) from an external switching Regulator waveform.
You have choice of shielding: standard 35 micron copper foil, 1/16 inch aluminum, 1/16 inch steel (mu of 1,...
- 35k
1
vote
Accepted
Inconsistent performance of circularly polarized antenna
The antenna as an axial ratio of 0.34dB which means this antenna is not truly circularly polarized. A true circularly polarized antenna will have an axial that is unity (0dB). Therefore the antenna in ...
- 2,657
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Why is a horizontal rod a full wavelength oriented radially to a broadcast antenna not the best receiving antenna
First, because the broadcast tower sends out vertically polarized waves and your receiver antenna is horizontally polarized.
Second, because the directivity of a lambda dipole is an —8— with the ...
- 14.4k
1
vote
Power received by RFID tag
The definition of the aperture of the antenna is
The aperture is defined as the area, oriented perpendicular to the direction of an incoming electromagnetic wave, which would intercept the same ...
- 134k
1
vote
Conceptual question about Frii's equation
You misspelt his name Friis, read his requirements and assumptions again.
The error is in geometry and the assumption this is far field not 1m near field.
Also with antenna gain, one measures the ...
- 148k
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FDTD simulation for beginners using matlab
in this book you can find Matlab implementations for FDTD. It specifically used for microstrip circuits but it might help you.
I hope this helps.
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Why do LF RFID tags use near field and why is reading distance longer with UHF RFID?
At 125 kHz, the far field begins at a distance of several km. There’s no chance a passive tag will work at this distance. At UHF, the far field begins at around a metre (300 MHz).
The Friis equation ...
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Why do LF RFID tags use near field and why is reading distance longer with UHF RFID?
It's about catching the radiating energy - transverse electromagnetic wave, which is very small at long distance. Therefore a long range RFID has to have its own power supply, battery like. The ...
- 24.5k
1
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Multimode cavity resonator
As has been mentioned in the comments, the resonance modes in your box will not be predictable and will be different for an empty container than for the container filled with pallets and will vary ...
- 753
1
vote
Accepted
Distance requirements in antenna arrays?
The antenna array spacing and thus size is usually based on the wavelength of the signals of interest, not the radiating element length.
It's a geometry problem in the far field, with the ratio ...
- 4,851
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