Questions tagged [antenna-theory]

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

Filter by
Sorted by
Tagged with
0
votes
1answer
59 views

Solid angle for different E/H plane beamwidths

The solid angle formula calculates the surface area on a unit sphere, from projecting a rectangular patch onto the surface of a sphere. Image source This is calculated using the azimuth angle $\phi$ ...
6
votes
1answer
126 views

For a resonant 1/2 wave dipole, does the reflections being in phase with the applied signal cause the zero reactance seen in the feedpoint impedance?

For a resonant 1/2 wave dipole when used for transmitting, does the fact that the reflected waves on the antenna are in phase with the applied signal result in zero reactance at the feed point, or ...
0
votes
1answer
59 views

Is shortening a half wave dipole to make it resonant by removing the inductive reactance a good idea?

A dipole which is exactly one half wave length allows reflections within the antenna to be in phase with the applied signal. To me it seems that this situation gives an antenna which will produce the ...
0
votes
2answers
103 views

For an antenna when used for transmittiing, what is the optimum radiation resistance?

For a 100 % efficient antenna, the real part of the impedance is equal to the radiation resistance. If the antenna were a dead short with zero impedance then the radiation resistance would be zero. ...
5
votes
2answers
105 views

Modelling a folded dipole

I am looking at using NEC to model a $0.5\lambda$ rectangular folded dipole, for closely spaced larger sides (choosing a separation of $0.01\lambda$). In Antenna Theory, Analysis and Design by ...
0
votes
2answers
109 views

What exactly makes an antenna resonant?

When an antenna is resonant, the impedance seen at the feed point is purely resistive and has no reactance. What are the physical properties of an antenna that actually make it resonant and how do ...
-1
votes
1answer
83 views

How can a half wave dipole which has an impedance of 73 + j43 ohms ever be resonant?

Is it true that for a half wave dipole, cancelling out reactance using for example a gamma match does not make the antenna resonant at all, but rather just cancels out the reactance of what is ...
2
votes
1answer
42 views

Can I use a directional coupler to block reflected AC current from a mismatched antenna?

Is there any kind of directional coupler device such as you find in a SWR meter that only allows traveling AC waves of one direction to pass which i could use to block the reflected wave from my badly ...
1
vote
1answer
26 views

Can received and transmitted signals on the same antenna combine to produce standing waves?

Standing waves are seen on a transmission line when for example there is a change in impedance and a transmitted wave is reflected back from one end and then the incident wave and reflected wave ...
0
votes
1answer
82 views

If i transmit on the same frequency using two separate transmitters joined together will they both add up in a reciever to produce a stronger signal? [duplicate]

If i were to use a passive transmit coupler to connect two transmitters of equal power output to the same antenna, and connect one microphone to both transmitters, and then transmit on both at the ...
14
votes
1answer
2k views

Why do amateur radio operators call an RF choke a balun?

When using a balanced antenna such as a half wave dipole, with an unbalanced feed line such as coax, an RF choke can be used to block RF current emitted by the transmitter from splitting up at the ...
1
vote
1answer
64 views

Does an antenna work the same for pure sine waves as compared to other waveforms?

Antenna theory it seems is always described assuming that the transmitted or received signal being talked about is a pure sine wave usually at the resonant frequency. Standing waves for example are ...
1
vote
1answer
69 views

Can any one explain E,H plane definitions?

I read in some text books that E-plane is formed by taking constant azimuth angle and scanning elevation angle from -90:90. H-plane is formed by taking a plane perpendicular to E-plane. What is ...
2
votes
1answer
79 views

Is the voltage at the centre of a dipole zero only at it's resonant frequency?

For transmit, the voltage at the center of a dipole not cut in the center and fed with coax and a gamma match is zero in the center at the resonant frequency. This is why apparently a 'plumbers ...
0
votes
1answer
36 views

What is the effect of coil Q on a shortened dipole?

I made a small yagi, with the driven element being a coil loaded dipole. What is the effect of coil Q in this situation? The coils I built are 18 turns of 1.2mm enameled wire wound tightly with a ...
2
votes
2answers
134 views

Is an antenna resonant at the frequency of lowest impedance?

I understand that an antenna is resonant at the frequency where the capacitive and inductive reactance cancel out to 0. Only the resistive impedance remains at resonance. Does this mean that the ...
2
votes
0answers
54 views

Ferrite Rod Antenna Array?

The ferrite Rod is a reasonably effective Receiving Antenna for LW MW and Lower HF spectrum .It is well known that a ferrite rod is much more effective than an air cored coil of the same dimensions ....
3
votes
2answers
129 views

What kind of loop antenna is this, and what is the relationship between its diameter and wavelength?

At the bottom of webpages in the advertisement swamps I keep seeing this image of an antenna, accompanied by an offer that I won't be clicking on. But the antenna itself looks quite intriguing. It's ...
4
votes
2answers
132 views

Actual Impedance of a folded dipole at resonance

I am using a Folded Dipole which I bought when I first got my General License. It was advertised as an all band antenna. My results with it were less than the claims made by the makers to say the ...
5
votes
1answer
287 views

How does a Viper Antenna work?

Are any of you guys familiar with a "Viper" antenna? It came up in a recent discussion with club members for higher frequency bands (6m, 4m, 2m). I hadn't heard of it before and internet searches ...
2
votes
3answers
134 views

High Altitude Balloon Antenna Design

I'm designing a weather balloon with a club at college. We want to build the antenna from scratch to learn more about antennas but are at a loss as to which antenna design would actually work for high ...
2
votes
1answer
59 views

Gain of Yagi turnstile?

I am currently working on a system to communicate with amateur CubeSats. I have decided to use the turnstile crossed-dipole style yagi because it is relatively easy to construct and uses circular ...
0
votes
1answer
49 views

Can you measure how much radials you are lacking for HF vertical?

I have tried mount ham sticks on SUV and a convertible use trunk lid mount, especially on 40m on the convertible I notice the SWR changes from opening the door and close the door. Now I am quite ...
0
votes
1answer
70 views

Inverted L Feedpoint Height

I have this antenna EFHW 40-10 from Maple Leaf Studios. My current configuration: Inverted L with feed point 3m above ground, with "L" at 9m. I have 45 20-foot in-ground radials just below the feed ...
2
votes
2answers
79 views

Using two VHF antennas vs one because of a large obstruction

We have a VHF Omni directional antenna, 2.5 W and 119 MHZ (approximate) mounted on top of a commercial hanger. Access to the antenna is out of the question because of the lack of fall protection. ...
0
votes
1answer
72 views

Can i use an anaolgue IC switch to change a 10 m yagi's directivity by somehow combining received signals with different variable phase?

Can i use an analogue IC switch being triggered at the same frequency I am receiving on to change a 10 m yagi's directivity by somehow combining received signals with different variable phase either ...
1
vote
4answers
103 views

Which 10 m antenna will give the most rejection in one direction for received signals which are vertically polarized?

I want to null out a particular direction so that i can't receive some vertically polarized interference on 10 m coming from that direction. Which 10 m antenna will give the most rejection in one ...
-1
votes
1answer
75 views

How would I calculate aperture efficiency for an antenna?

How to calculate aperture efficiency for an antenna with the following parameters: Big reflector diameter= 24 mm Gain= 9.265 dbi Frequency= 11.60 GHz
4
votes
3answers
1k views

Vertical Yagi spun at 1000 RPM: gain properties?

If I were to mount my 10 m vertical Yagi on a pole with a motor attached at the bottom with the appropriate fastening and coax mounted via electrical brushes, if the Yagi is spun at say 1000 RPM would ...
2
votes
3answers
100 views

Why is self-resonance important in a loop antenna?

I visited a "small loop antenna" calculator web site today and fed in my horizontal loop gepmetry, curious to see what it would say. 2" dia wire, 72' circumference, 3.935MHz. Interesting results, ...
2
votes
2answers
60 views

Will ferrite rings around a metal pole hide it in an RF sense from my vertical 10 m Yagi?

If i mount my vertical 10 m 4 element yagi directly on a metal pole so that the pole is between the elements and so messes up the radiation pattern and input impedance, if i put lots of type 43 ...
2
votes
1answer
201 views

When I am told that a dipole must have a determined length, does that include the space between both elements?

I am trying to build an antenna for receiving NOAA satellites and I need to build two 137,5MHz dipoles. When I enter the frequency and width of the wires in a calculator, I obtain that $λ/2=1.09\,\...
4
votes
2answers
80 views

Basic antenna matching theory?

I'm fairly new to antenna matching, other than having built a base loaded vertical. I'm also new to EZNEC and I tried to simulate an horizontal loop. I arbitrarily chose a 10x10M loop, so I added 4 ...
2
votes
2answers
76 views

How to estimate a dipole feedpoint impedance?

An ideal dipole, at resonance, will have an impedance around 73 ohms. A folded dipole, around 280 ohms. How can I calculate the impedances when not at resonance? Let's assume I have a span of 15M in ...
0
votes
4answers
98 views

Can I make signal transmitter without decoder?

I'm sorry if my title seems weird but I just started to learn about signal transmitting and I don't know where to start I'm searching about simple ways to make diy radio but I can't really ...
5
votes
1answer
91 views

Counterpoise wire voltages?

One practice which seems common when operating temporary or portable QRP, SOTA, etc., is to throw a counterpoise wire out on the park lawn or shrubbery, mountaintop or hillside or parking lot ground, ...
4
votes
1answer
54 views

Voltages in a beam antenna's passive elements?

This question has good answers for the voltages reached in portions of a dipole antenna during transmit. In a beam (Yagi or Yagi-Uda) antenna, do points along passive or parasitic elements (...
2
votes
1answer
67 views

What sort of antenna would use a bicone or lozenge-like arrangement of vertical wires?

In another QA here, there's a picture of an antenna I identified as a "discone": What are these antennas used for? One commenter noticed that antenna was actually a "Discone, but no disc, just the ...
2
votes
2answers
121 views

Will using a 1:1 balun at the feedpoint of a center feed dipole result in no common mode current on the outside of the coax?

Will using a 1:1 balun at the feedpoint of a center-fed dipole when using coax result in no common mode current on the outside of the coax ?
0
votes
1answer
76 views

Passive antenna system as a Wi-Fi repeater [duplicate]

I want to extend WiFi signal using a passive repeater between two isolated boxes (have to make both box wireless). Transmitter antenna from box A is placed in the gap between box A and B. In the same ...
5
votes
3answers
189 views

ARRL handbook as a reference for all your radio learning needs?

Looking to take up learning understanding everything from basic electronics to how today's wideband radios work, so that I can build my own radio systems (not just ham radios), and talk radio concepts ...
2
votes
2answers
75 views

resonance vs resonator in antenna

Resonance in electronic means: reactance of zero. (maybe wrongly/correctly someone's calling the minimum VSWR, the resonance of antenna! and this cause confusion) I've heard in Antenna Design for ...
4
votes
4answers
205 views

Why does an RF Amplifier fail when the SWR is high?

Exactly why does an RF output transistor fail if the SWR is bad ? Is it A because the impedance mismatch between the transmission line and the antenna results in maximum power not being transferred ...
3
votes
0answers
43 views

How to simulate two antennas in 4nec2

I need to simulate 2 helix antennae placed side by side, and see the resultant radiation pattern. But after adding the second antenna with a separate and when I try to simulate 4nec2, only simulated ...
3
votes
4answers
161 views

How does the thickness of the radiator affect an antenna

Another question (Metal for antenna construction?) covered some aspected of this question, but the answers didn't exactly answer it, so I'll make it specific. Given 2 dipole antennas, resonant at the ...
1
vote
3answers
287 views

How to calculate impedance in antenna design's practice?

I would like to make a match half wave length (λ) dipole antenna (or probably a short dipole antenna). So I would like to make it by measure using LCR meter. What I am still confuse is about what is ...
2
votes
4answers
199 views

What is the maximum and minimum of antenna gap of dipole antenna?

Consider the picture below is design of half wave length (λ) dipole antenna. I read some explanations saying that it is the best design to get the optimum transmit power. Half wave length (λ) is from ...
4
votes
0answers
74 views

Dipole loading coil winding directions?

A single inductive loading coil in a vertical or a pair of loading coils in a dipole are commonly used to match a given total antenna length parameter to a given frequency wavelength (where the ratio ...
3
votes
1answer
126 views

How do I design a dual band LPDA antenna?

Im not sure if this is the best place to ask a question like this but its the best place i could find. My goal is to build a dual band antenna similar to this one. That covers ...
3
votes
1answer
91 views

What type of antenna is this?

I have very little knowledge about antennas (I just read about simple dipoles and monopoles recently) and I need to buy a directional antenna for my wireless device. I have found a cheap antenna (I ...