Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [far-field]

17 questions
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3 answers

What's radiating on my PCB?

I recently did a proper EMC test on a PCB of mine. It failed the test, and seems to be radiating in the 300MHz - 1GHz region, with peaks every 50MHz, and little peaks on the 25MHz. Looking at the near field, you can clearly see lots of 25MHz…
Rocketmagnet
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Transformer basics: Why don't they shift phase by about 90°?

I learned that current is induced in a conductor by a changing magnetic field. According to this, it would follow that the secondary voltage (sinusoidal input) of a transformer should peak when the primary current is changing fastest — that is at…
Nicholas Bodley
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How is the minimum reasonable distance for the far field of a dipole antenna calculated?

First let me try to explain what I think the near field is about: At very close ranges, due to the differences between instantanous voltage and current on each small segment of an antenna at any given time, the EM field is not uniform (spherically)…
Xynon
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Horn antenna Radiation pattern

Ok This might sound dumb but I am trying to get an equation for the radiation intensity of a pyramidal horn antenna in spherical coordinates. I got a whole bunch of books and they all have the same equation: $$ \mathbf{E}_\theta = \frac{j\, e^{-j k…
RBF06
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How to calculate far field distance from an antenna

I understand the formula for calculating the far field distance from an antenna is: Distance = (2D2)/λ Is the D in the above equation the length of the antenna under test (antenna under test is a small PCB antenna)? In which direction (1 or 2 in the…
MRB
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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 meant to be used in the far-field range? This is…
JoeyB
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Relationship between electric field at aperture and field at distance

I'm new to this forum and turned here because I have no other help to turn to. In studying antenna theory and I came across the relationship between E0(Electric field at aperture) and Er(Electric field at distance r). It was stated as follows: $$…
user3889963
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Antenna polarization and loss factor

I am trying to solve the following problem: I know that in the +z direction: linear polarization requires the field vector to have: one component OR two orthogonal linear components that are in phase or 180 degrees (or multiples of 180) out of…
yellow_watermelon
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Rayleigh distance of array antenna

Far field zone of a single antenna can be determined by using the equation below. $$R>\dfrac{2D^2}{\lambda}$$ Where D is the biggest dimension of the antenna. This equaiton is suitable for single antenna. But what if there are more antennas than…
Aldrich Taylor
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Side lobe level of an aperture antenna

There is a electric field in the far zone of the rectangular aperture antenna as shown below. Antenna lies along the xy plane. $$E_{\theta}=\dfrac{jke^{-jkr}}{4\pi r}\dfrac{sin(0.5\lambda k sin\theta sin\phi)}{ksin\theta…
Aldrich Taylor
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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 forward. But would it be possible to use the far…
divB
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finding polarization of radiated far-zone electric field

I am given a question in which I have to find the polarization of the radiated far-zone electric fields when phi is 0 and 90. Why are the following formulas used respectively? For phi = 0 $$ E_\theta = jn\frac{kI_0le^{-jkr}}{4\pi r} cos\theta …
Muhammad Ahmad
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The electric and magnetic components of far field EMR and shielding thereof

This is a newbie question. I'm pretty sure of the answer, but I would like confirmation. I found this thread in this forum that came close to what I was looking for, but I think my question is different. I want to shield against ingress of far…
dcorsello
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Phased array minimum size

I want to know two things,how big does the phased array needs to be to form proper beam and what is the smallest area the beam can be focused.I learned little bit about lasers and with focal lense,the smallest spot that it can be focused is 1…
wav scientist
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What are the extra lines on this farfield plot?

This is a plot from CST microwave studios of the farfield beam pattern of an antenna. I'm having trouble understanding why the plot isn't single-valued (2nd red circle) and also why there are blue lines. Any help would be much appreciated
boson
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