Questions tagged [em]

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416 views

Insight into cavity resonators

Modes of a waveguide As shown in the link above, they show how these modes work for various values of m, n, and p. However, where is the antenna/ source of radiation placed within the cavity? From ...
5
votes
3answers
295 views

Visual understanding of EM fields within a rectangular metal container

I have the following scenario setup inside a rectangular metal container. The container size is 12.03m by 2.39m by 1.84m (lxbxh). Additionally, inside the container I have placed 4 antennas equally ...
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3answers
109 views

Why is a horizontal rod a full wavelength oriented radially to a broadcast antenna not the best receiving antenna

I have always struggled to get a good physical understanding of Electromagnetic waves. I've done the whole Maxwell's equation approach, wrote boundary element solver tool but cannot rationalize that ...
1
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1answer
80 views

Electromagnetic wave equation for GPS waves

Recently, I came across a source which stated the model of a GPS L1 wave was: My question is, how was this equation derived?
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1answer
18 views

How do I EM-Extract a subcircuit and define a different em/drawing-layer than the original circuit in AWR?

I have a 4-layer project in AWR/MWOffice and have built a parameterized microstrip inductor schematic (named "spiral") with a "Line Type" of layer1 that I wish to reuse on another ...
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3answers
2k views

Distance requirements in antenna arrays?

Antenna array is a broad term and it encompasses at least the following concepts: MIMO or massive MIMO: for spatial multiplexing beamforming: increasing the SNR (at transmitter or receiver) by ...
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0answers
36 views

Using a far field UHF RFID in the near field range

I have a 902 MHz to 928 MHz UHF 8dBi far-field RFID antenna connected to a reader. I want to read RFID tags. What will be the consequences if I used this UHF antenna in the near field range when it is ...
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1answer
51 views

EM propagation analysis

I have an antenna which runs at 917MHz located inside a metal structure that measures in at 6m long, 2m wide and 1.9m high. The exact location of this antenna will be in the center against the length ...
0
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4answers
101 views

Simulation of 2D vs 3D electromagnetic waves

If you using a simulation tool that allows you to simulate behaviour electromagnetic waves in an environment. What differences are there in terms of doing the simulation in 2D vs 3D? Does doing the ...
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1answer
52 views

Question on spark gap transmitter circuit

I am trying to understand how basic electromagnetic communication works. From what I understand, spark-gap transmitters were the first wireless devices made by man. A couple of circuits I found online ...
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2answers
128 views

How, exactly, does the 'input signal' wave(s) modify the carrier-wave of a radio signal? [closed]

I cannot find a simple (or really, not-so-simple) explanation of how mixing the high-frequency carrier wave with the lower-frequency input signal works... Is it entirely due to constructive and ...
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1answer
64 views

Power calculation from E and H field

I am using gprMax to simulate my design. The design is shown in the picture. It consists of an RFID system inside a steel structure. The transmitting antenna is placed in the middle of the container ...
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1answer
56 views

E fields and M fields in Near Field

I am reading a textbook that mentions that small loops with high dI/dt on a PCB tend to produce predominantly magnetic waves and stubs with high dV/dt tend to produce predominantly electric waves in ...
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2answers
69 views

Why do LF RFID tags use near field and why is reading distance longer with UHF RFID?

Why do LF/HF RFID tags use the near field (magnetic coupling) and not the far field? Well, I guess it's easier. The two antennas can just be modeled as a "transformer" and power transfer is straight ...
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1answer
43 views

Inconsistent performance of circularly polarized antenna

I have a circularly polarized patch antenna for an RFID reader, with a gain of 8dBi and bandwidth from 914MHz to 919MHz and an axial of 0.34dB. I have read that using a CP RFID patch antenna means ...
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1answer
40 views

Power received by RFID tag

Power calculation from E and H field Following from the previous post above. The user provided me with some assistance however I am still a bit unclear on how to apply the equations provided. Could ...
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1answer
57 views

Conceptual question about Frii's equation

That's a pretty basic one but for some reason I am stuck now: Suppose I have a transmitter that transmits Ptx=4W_EIRP with an ideal, omni-directional antenna. The power applied to the antenna ...
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2answers
243 views

FDTD simulation for beginners using matlab

My previous posts are as follows: 1.Mitigation of dead zones when applying circular polarized antenna 2.Standing waves modes inside a cavity resonator 3.Visual understanding of EM fields within a ...
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1answer
40 views

Not full-wave signal transmission?

Is it possible to transmit half-wave signals repetitively, like repetitive "north" magnetic fields like going from 0-1 Gauss "north" and repeat however many times per second without going 0-north-0-...
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1answer
32 views

Finding constant in electrostatic equation given only charge

So in a region of free space with zero charge, all I'm given is that the electrostatic potential V is given by: $$V(x,y,z) = kz(x^2) y + 2y - 6y(z^3)$$ [Volts] To find the constant k, would I have to ...
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0answers
46 views

Need RF advice (NFC antenna VS GND pour)

I'm currently working on a design who involve a NFC chip (ST24DV) who need to be on the board as it's used to communicate with a smartphone. Here is the picture of the antenna: There is a LED on the ...
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0answers
38 views

A circularly polarized EM wave is perfectly absorbed by any interface?

According to the Fresnel equations, the effective reflectivity of an arbitrarily polarized electromagnetic wave is given as: $$ \Gamma = \frac{\Gamma_p + \Gamma_s}{2} , $$ where \$\Gamma_p\$ and \$\...
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0answers
67 views

Detection range of unintentional emissions by battery powered video recording devices?

I have read about unintentional radiators, but wonder about what their unwanted emissions detection range can be in low background noise, referring to battery powered motion-sensor activated video ...
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0answers
64 views

Effects of wood on UHF transmission

I have set up the following scenario in gprmax. From the results obtained using the software, I realized that when I increased the wood thickness the power received at the receiver increases instead ...
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0answers
51 views

Interpretation of data

I hope this question meets the standards of this platform, if not please inform me of how I can improve it. I was trying to design an antenna and I have done so. I am planning on using this antenna ...
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1answer
87 views

Multimode cavity resonator

From my previous posts Insight into cavity resonators, Visual understanding of EM fields within a rectangular metal container I have slowly gained a better insight into cavity resonators and thereof. ...