Questions tagged [antenna-theory]

Designing antennas, selecting antennas for specific applications, properties of a given antenna design.

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How to determine the best length for a short dipole antenna

If I were to design a dipole antenna that's significantly shorter than usual for the frequency, how can I determine the best length to use? In other words, given a frequency and a maximum length (...
mrog's user avatar
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What frequencies can a GNSS (Global Navigation Satellite System) antenna pick up?

Am sure that a GNSS antenna can pick up other frequencies than GNSS ones, so is there anyone who tested that theory?
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What is the antenna design and gain for the WA1 U/V band antenna on the ISS?

My son KJ7NLL is working to contact the ISS using an antenna we built together, and we were wondering the approximate minimum transmission power to reach the ISS. If I understand correctly (and ...
KJ7LNW's user avatar
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Operation of an off-center fed vertical for 10 meters

I am looking for a smallish omni-directional 10 meter antenna for installation in my attic. I notice that MFJ sells one called MFJ-1790. They call it an off-center fed vertical, and it has two ...
gschro's user avatar
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What is the apparent AC voltage source caused by a mismatched impedance on the antenna or transmission line?

From Understanding how antenna mismatch can damage a transmitter "The reflected wave appears to the transmitter's antenna port... as an AC voltage source... whose magnitude and phase depend on ...
SRobertJames's user avatar
2 votes
2 answers
248 views

Understanding how antenna mismatch can damage a transmitter

I know it's important to tune an antenna to the same impedance as the transmitter for maximum power transfer. But I've read that if you don't do so, you not only get less radiated power, but you can ...
SRobertJames's user avatar
1 vote
1 answer
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Combining antennas

Is it possible to combine 2 antennas, each being half the length of a normal antenna for a given band. To be connected to 1 mobile radio. Giving you 2 shorter antennas rather than 1 long antenna, ...
Jake Koenig's user avatar
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3 answers
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Does Velocity Factor pose a significant cable loss?

We know that a lower Velocity Factor translates to using shorter runs of cable in resonant circuits. That apparently means that there is resistance to the flow of electrons, slowing them down. So ...
Dax's user avatar
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How do these ceiling mount dome antennas work? Are these discone antennas or horn antennas?

The small cone is connected to the larger one. The coax center cable is terminated into the small cone and the coax shield into the larger outer cone. The screenshots are from this video https://www....
Mavin's user avatar
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Off-center fed long wire antenna

I want to feed a horizontal wire antenna (approximately 150' long at 50' or more above the ground) for multi-band HF operation with an off-center (25-33%) feedline. The element wire will have no ...
Allen's user avatar
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LTE (4G) - Which external/outdoor antenna type is the best?

I've seen several antenna types out there, but I can't know for sure which model is the best for external/outdoor LTE (4G) use. I have to say that I don't understand anything about LTE (4G) antennas......
Eduardo Lucio's user avatar
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Antenna Aperature for out-of-band frequencies

I am doing some calculations where I determine power at the input of Rx given some field strength at the antenna. I have a question about the antenna aperture: $A_e = D\frac{\lambda^2}{4\pi}$ $D$ is ...
oogieoogieful's user avatar
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LTE (4G) - Is two (or multiple) antennas better than one?

I have two antennas. A "multiband" (1710~2170 Mhz, 22 dBi)... ...and a "fullband" (700~2600 MHz, 15dBi)... Taking into account that my modem (router) is "fullband" and ...
Eduardo Lucio's user avatar
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2 answers
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Relation of Emitted Wave in Far Field Regions and Radiation Pattern with Antenna Design

As this post from electronics stack exchange suggested, EM wave emitted by the antenna tends to become spherical waves(plane wave with a local analysis) in the far field region regardless of the shape ...
Felix's user avatar
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How does the waveform of electromagnetic wave affect the design of an antenna?

This is a question I thought about when trying to understand a design of an antenna. For different kind of waveform of electromagnetic wave propagating through space, how does one modify an antenna ...
Felix's user avatar
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Would it be possible to light up a bulb wired one side to a transmitting antenna?

Would a light bulb light up if wired to the end on an antenna ? If you would connect a light bulb on one of its poles to a quarter wave antenna like in the schematics below, would the bulb light up ...
JeanMi's user avatar
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2 answers
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How can cross-polarization loss be determined given the angle between two antennas?

This question addresses the case where two antennas are exactly 90° cross-polarized, but not other angles. How can I determine the theoretical, and estimate the actual, attenuation from cross-...
kj7rrv's user avatar
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Calculating a real antenna gain from electric field strength?

Could someone please tell me if it is possible to measure the antenna gain simply by placing a field strength meter at a selected distance to my antenna, knowing the power applied to the antenna. ...
Icaros's user avatar
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2 votes
2 answers
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Balance of gamma / delta match

A center fed dipole, with equal arm lengths, is a balanced device. If it is fed using a gamma match - does it change (the system) to be unbalanced?
Jan Hus's user avatar
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5 answers
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Minimal SWR at resonance

Why does a minimal SWR NOT indicate antenna resonance? Would SWR 1:1 be required to indicate antenna resonance?
Jan Hus's user avatar
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What frequency ranges are most common for Amateur radio astronomy and why are most parabolic antennas tuned to such high frequencies?

What frequency ranges are most common for amateur radio astronomy? I am mostly interested in radios for the purpose of astronomy. In general I was expecting that the lower frequencies would be more ...
Hack-R's user avatar
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2 answers
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Antenna reciprocity how does an antenna increase receiving range?

According to Wikipedia antennas are reciprocal unless they're constructed of nonreciprocal materials. There are a multitude of mathematical formulas which unfortunately I'm unable to understand due to ...
icyli2's user avatar
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5 votes
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does the shape of an antenna ground plane matter?

I would like to test a tranceiver setup I created before I mount it in my car. In my backyard, there's a length strip of metal; 10m in length, 10cm wide. Now I wonder if I can use that as a ground ...
Folkert van Heusden's user avatar
6 votes
2 answers
253 views

Why do biconical antennas have a wide bandwidth?

Why does a horizontal biconical antenna have a wider bandwidth than a dipole of similar length? What's the physics behind the biconical geometry having a bandwidth uncoupled from its length in ...
hotpaw2's user avatar
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1/2 wave dipole instead of 1/4 wave + ground plane

I have a transceiver operating at 150MHz using a 1/4 wave vertical whip and horizontal ground plane at 90 degrees. My end user doesn't like the antenna sticking up in the air (trip hazard) so I'm ...
P_J's user avatar
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For an HF antenna I am using a mesh dipole (10sq meters) with surprising good results on 7MHz how does it work?

I try to use attic antennas I experimented an antenna made of 10sqM of chicken grid with excellent results how to calculate the aperture of such an antenna the first resonance is 3.6 MHz and the use ...
Paul's user avatar
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2 votes
2 answers
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Why does my 7 MHz antenna trap have an SWR of 8?

I made a 7 MHz antenna trap. On testing it the cut-off point was 6.687 MHz which is about right but the problem I've got is the SWR was an 8 and wouldn't go down to a resonant SWR. What have I done ...
chris cutting's user avatar
5 votes
1 answer
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What lengths of counterpoise is suitable to support a 58 foot "random wire" antenna?

I am a technician interested in building my first antenna. I want to explore HF bands, 160m - 6m. Quick impedance calculations indicate that a 58 ft "random wire" antenna could work for this....
mcandre's user avatar
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2 answers
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Understanding Coax Impedance when Connected to Reactive Load

The 50 ohm characteristic impedance of my coax is only "characteristic" if it's terminated with $ 50 + 0j$ load. So when the coax is connected to an antenna that is fairly reactive like $ 23-...
wbg's user avatar
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DIY Short Vertical Wire Loaded Antenna: Using 20 Ohm Resister to Widen Q

I've been working with Xnec2c to model a 40 meter vertical antenna I want to build for field QRP. This antenna is short at 25 feet and uses a 1:1 unun at the base with 4 radials. The model has the ...
wbg's user avatar
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Link budget validation for a UHF satellite ground station

I built a UHF satellite ground station. It has a yagi with G=16.1dBi and an LNA with G=20.1dB. It’s a 430 - 450 LNA with NF=0.68. The RF cable, rg174/u has I think close to a 1dB/m, which would mean ...
Moses Browne Mwakyanjala's user avatar
1 vote
2 answers
174 views

How is it possible for a halfwave dipole antenna to be resonant?

I've been learning about antennas recently and I have some questions about the halfwave dipole antenna. My first question is about its resonance; as I understand it everything that oscillates has a ...
Filip Timko's user avatar
2 votes
4 answers
1k views

Is an off-center fed dipole (and/or doublet) inherently unbalanced?

Does a balun/choke have to "work harder" in an off-center fed dipole than when the feedpoint is at the center? Or do the standing waves that develop keep the antenna balanced electrically ...
natevw - AF7TB's user avatar
2 votes
3 answers
721 views

Why does an HF "monopole" need dozens and dozens of radials while a VHF/UHF "ground plane" antenna only needs four?

It's a bit counter-intuitive that for an HF vertical antenna (such as a quarter wave monopole) the best advice is to put as many radials and as close to the proper length as possible. The typical VHF/...
natevw - AF7TB's user avatar
0 votes
3 answers
655 views

ELF antenna receiver build instructions?

I built a vlf receiver in the nineties but good grief, that's a long time ago and have looked very little at receivers since. I'm interested in frequencies from 12 - 18 Hz. Looking at the following ...
SeanJ's user avatar
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9 votes
2 answers
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Why are longer antennas not suitable to pick higher frequencies?

I know that the length of an antenna depends on the wavelength of the frequency it's trying to receive. A higher frequency needs a shorter antenna and vice versa. I can see that with a high frequency ...
Dan's user avatar
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1 vote
2 answers
276 views

Small shortwave (20MHz) directional antenna design

I'm trying to do some basic radio astronomy experiments, and I'm currently working on picking up radio bursts from Jupiter. These are emitted at around 20MHz; for all intents and purposes, Jupiter is ...
T.S's user avatar
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3 votes
4 answers
217 views

Is it worse to use an antenna tuner on an already-loaded short monopole?

If I had a good transmatch and wanted to use a spare CB antenna on the amateur HF bands, would I be better off bypassing its tuning coil completely? One ham pastime is using an antenna tuner to match ...
natevw - AF7TB's user avatar
1 vote
2 answers
507 views

Can fanned/parallel endfed antennas be used to get higher gain in some directions?

I have two pieces of antenna wire which are roughly 10 m long, with banana plugs at the ends, which I bring to hang in the trees when operating portable. I also bring a 49:1 unun and hopes that my ...
EdvinW's user avatar
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5 votes
2 answers
1k views

Is the original satellite dish "ruined" when a slot antenna is cut into it?

A fun vertical antenna can be made by cutting a horizontal slot in a satellite dish, as documented in e.g. http://www.w6nbc.com/articles/2016-3QSTdishslot.pdf and discussed in How does a slot antenna ...
natevw - AF7TB's user avatar
4 votes
2 answers
817 views

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 ...
Bitbang3r's user avatar
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2 votes
1 answer
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How do phased array antennas work when they produce spot beams?

Background In a lot of literature regarding satellite communications with phased arrays, you'd see this kind of image: Conceptually, I get the basic concept of how this works - a bunch of small ...
0xbad1d3a5's user avatar
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0 answers
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Keysight ADS User-Defined Models to AWR/Virtuoso

everyone! In ADS Keysight it is possible to create an item model - the so-called User-Defined Model. This is C++ code that describes the Y-matrix of the component. Is there the same possibility in AWR ...
Евгений Федоров's user avatar
2 votes
4 answers
133 views

What's the methodology of MDF magnetic field antenna?

I get a MDF 9400 magnetic field antenna from school. I am not able to disassemble this flat antenna to take a picture. I am not sure if this antenna detect only magnetic field. I am not sure if ...
kittygirl's user avatar
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0 votes
3 answers
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Follow Up on a previous question- Transmit antenna on HF band

I had asked a question in a previous segment and the link is provided below Antenna Size limits at 2-30 MHz (10 m to 150 m wavelength) I think i have some more clarity on the question I wanted to ask. ...
AmateurRadioFan's user avatar
5 votes
6 answers
2k views

Does an antenna pick up signals of all frequencies or only its resonant frequency?

I heard that an antenna picks up signals of all frequencies, and then these signals are filtered by a circuit using an inductor and capacitor, and that this is how a radio is tuned. However, I also ...
Urthona26's user avatar
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What is the differece between a large loop antenna and a small loop antenna in terms of their response to an electromagnetic wave?

There is something that I don't get. I read that a small loop antenna (also called magnetic loop) responds more to the magnetic field than a large loop antenna does. I was wondering why this is the ...
kinu's user avatar
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7 votes
1 answer
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How does a Large Loop Antenna work physically?

I am learning about loop antennas at the moment. I read that the response of a small loop Antenna is proportional to the rate of change of magnetic flux through the loop which causes a uniform current ...
kinu's user avatar
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3 votes
0 answers
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Turnstile antennas with a "single-point feed": what's the antenna theory behind this, and how do I build/model it?

The conventional turnstile antenna uses a 1/4wl phasing line between the crossed elements, to get the required phase shift. 4nec2 includes an example file, though, of a circularly-polarized Yagi using ...
1200bps's user avatar
  • 31
6 votes
2 answers
301 views

Power rating of a selfmade air coil

A colleague was winding an air coil himself. It's a 110µH coil with 200 windings for an 80m antenna, intended to be used on a 600 W transceiver. He used a copper lacquer wire with 0.6mm diameter. ...
Thomas DK3TU's user avatar

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