Questions tagged [far-field]

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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 = (2D^2)/λ Is the D in the above equation the length of the antenna under test (antenna under test is a ...
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What is >> (double chevron) in far field communication

I keep seeing this notation with no justification or explanation as to what it is – it appears to be being used as greater than but I don't know why > isn't sufficient. Didn't want to ask it as a ...
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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 ...
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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 ...
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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 ...
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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 ...
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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_\...
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1 answer
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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 ...
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3 answers
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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 ...
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1 answer
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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 ...
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3 answers
529 views

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 ...
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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 ...
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4 votes
2 answers
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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 ...
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1 answer
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near field power density formula for a dipole antenna

I am looking for a formula for near field power density from a dipole antenna antenna. Is cylindrical model is sufficient? Do I have to consider ground reflection too? Please share your ideas?
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2 votes
2 answers
863 views

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 ...
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43 votes
3 answers
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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 ...
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