Questions tagged [antenna-theory]
Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
99 questions
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What is the relationship between SWR and receive performance?
If an antenna analyzer shows 1:1, does that mean it's an ideal receiver as well? And what about the converse, will a well performing receive antenna show a 1:1 SWR?
I've wondered this for a while, ...
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What is a Gamma match in the context of the driven element of a Yagi antenna?
How (and why) does a Gamma match work, when used on the driven element of a Yagi antenna? As shown here:
(source: http://www.iw5edi.com/ham-radio/?2-element-yagi-for-10-meters-band,49)
The article ...
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What does the addition of a shield to a small loop accomplish?
A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the ...
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How does moving a feedpoint off-center in a dipole affect the resonant frequency and resistive load?
Specifically, I understand that OCF dipoles change the SWR, but does it do this via reactance or resistance, or both?
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What is the peak voltage at the tips of a dipole antenna?
What is the peak voltage present at the very end tips of half-wave dipole antenna in free space, and how might this peak voltage relate to transmitter type, transmitter power, RF frequency vs. antenna ...
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When and why does the size of a ground plane or radials matter?
Consider these three cases:
My understanding is that when building or installing an antenna designed to operate over a ground plane (e.g. a quarter-wave vertical), the size of the ground plane does ...
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4
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Measuring actual feedpoint impedance for a given frequency
Background
I'm attempting to tune an antenna with my NanoVNAv2.
I calibrated it using the included open/short/(50-ohm)load standards by screwing them directly onto the NanoVNA one by one and running ...
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4
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Does a resonant antenna work better than a non-resonant antenna?
Some books on antenna fundamentals i've read recently say that, for a half wave resonant dipole when transmitting for example, the traveling wave of movement of charges reflected back from the ends of ...
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What is the impedance of an end-fed half-wave antenna?
It is my understanding that the feed-point impedance ($Z_a$) of an end-fed half-wave antenna is dependent on at least the following factors:
$L_a$: The length of the radiating element of the antenna.
$...
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What is the advantage of making an antenna resonant?
I am constructing a small loop antenna; apprx 4' diameter, will be used with an antenna tuner (mounted at the feedpoint) and 100W transmitter, and hope to use it on 20m, 40m, and maybe other bands if ...
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What is the aperture efficiency of an antenna?
For reflector antennas, I see a number called aperture efficiency. What does it mean?
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What happens to a vertical Yagi when you mount it on a vertical metal pole?
How much difference does a metal pole make when it's sitting in the middle of all the lower elements of my beautiful new highly optimized to the max YO.EXE 10 m yagi ?
I get it that the closeness of ...
- 3,837
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How do Handheld antennas work without ground?
Dipoles have the 2 wires going to each leg of the antenna completing the circuit.
Big AM towers use the second wire as a ground plane
But how do handheld rigs transmit and receive with just one wire ...
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Calculating Antenna Length on the FCC Exam vs. in Reality
I have seen the following formulas for calculating half and quarter wavelength antennas:
Formula for $\frac{1}{2}$-wavelength antenna (in free space):
\begin{equation}
\mathrm{Length~(feet)} = \frac{...
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How does a folded dipole work?
A folded dipole is like an ordinary dipole, but with the ends extended and folded back, until they meet. Although it looks like a loop, I'm told it behaves similarly to a dipole.
How does this thing ...