Questions tagged [antenna-theory]

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

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85 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 ...
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2answers
712 views

If one were to add reflector elements above and below a dipole would it change the direction to horizontal?

Since adding a reflector and a director horizontally to a dipole (as in a three element Yagi) causes the beam to reflect horizontally, what should happen if reflectors above and below the dipole were ...
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2answers
108 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. ...
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1answer
132 views

Can I make ferrite paint? Will it shield my antenna from my roof?

I have a 3 element vertical Yagi mounted on a rotator, and in one direction the roof of the house gets pretty close and messes up the SWR a bit. If i mash up a few type 43 material ferrite cores and ...
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2answers
233 views

What is the theoretical and actual cross polarization attenuation from horizontal to vertical polarization?

Can anyone tell me what the theoretical and actual cross polarization attenuation from horizontal to vertical polarization is ? The reason i ask is that i have the idea that for receive a vertical ...
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2answers
114 views

Does a vertically or horizontally polarized electromagnetic wavefront have a thickness?

Does a vertically or horizontally polarized electromagnetic wavefront have a thickness ? Or is it really thin and just the height or width of it's wavelength ?
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1answer
93 views

Directional antenna overlapping main lobes

In a 2-Rx by 2-Tx directional antenna system, say both transmitters are transmitting concurrently as in Fig. The main lobes from the two transmitters overlap. How does this affect the resultant signal ...
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1answer
79 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 ...
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1answer
55 views

Can radio waves be made to travel as or along a particle beam? [closed]

Can a laser be used as an antenna? Can a beam of any type extend transmission distance of an electromagnetic field? https://medium.com/starts-with-a-bang/this-is-why-the-2018-nobel-prize-in-...
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1answer
490 views

How does a gamma match on a dipole work as a balun?

I have a resonant half wave dipole which is one continuous length and not separated in the middle, fed using a gamma match, and with the braid of the coax joined to the exact electrical center of the ...
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2answers
656 views

Do the radials of a quarter or 5/8 wavelength antennas connect to the braid of the coaxial cable?

I'm studying for my foundation license (in the UK) and I have these diagrams: Do the radials in a quarter or 5/8 wavelength antennas connect to the braid/shield of the coaxial cable? If so, how does ...
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1answer
68 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 ...
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1answer
74 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 ...
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4answers
120 views

Cell tower identifier antenna isolator cannon

There are several cell towers on the hills around me. Usually I just walk around their base in a circle with one of the many CellID apps to get their ID. Then I can impress my friends, "That's tower ...
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1answer
450 views

What EXACTLY does front to back ratio mean?

For a yagi antenna for example, what does front to back ratio mean exactly ? Does it mean the reverse gain at 90 deg behind the antenna compared to the forward gain at 90 deg in front of the antenna ?...
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2answers
246 views

Does antenna array structure effect overall radiation resistance?

If we consider a basic half wave dipole array does the radiation resistance of array depend on distance between two elements and phase we feed?
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1answer
665 views

Which matters most in a fan dipole: Overall linear length or actual wire length?

I'm in the midst of constructing a fan dipole for 80, 40, 30, 20 and 10 meters. I have everything laid out and am about to start cutting wire. I have an ugly balun (RF choke) wound at the feed point ...
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1answer
69 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 $\phi$ ...
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1answer
39 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 ...
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1answer
51 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 ...
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1answer
89 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 ...
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2answers
197 views

Does a horizontally polarised yagi antenna have the same front to back ratio for horizontal and vertical received signals?

Can anyone answer this question : I have a 4 element yagi antenna which is horizontally polarized. Let's say it has a front to back ratio of 20 dB. Does that front to back ratio apply to received ...
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2answers
204 views

antenna theory for beginners [closed]

I am new to amateur radio and am having trouble getting my head around antenna theory. Can anyone suggest a good 'introduction to antennas' that doesn't get too technical? Thanks.
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1answer
427 views

Gain in long wire antennas

DARA (you know, Hamvention) TNG is looking for projects. Thursday, I will be proposing building and characterizing a vertically-polarized 1 wavelength on a side reentrant rhombic. Since in doing the ...
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1answer
56 views

Transmission Line Model of Co-ax Lines

I have got 2 questions on transmission line. In coax line, the centre wire is Copper, and the outer line is Aluminium, as far as I can see in the coax that I have. I have got couple of questions on ...
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1answer
82 views

What parameters are currently possible in a directional antenna less than 5mm long?

I'm curious what kind of directional antennas could fit inside a cell phone, which would require it to be 5mm or less in its longest dimension. I know that the length of a directional antenna is often ...
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2answers
128 views

How can a vertical Yagi for 10 m be mounted on on a vertical metal mast and be made to work properly?

From a reply to a previous post I've been told that a horizontal tube half a wavelength long mounted right at the junction between the boom on a vertically mounted yagi and a vertical metal pole will ...
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1answer
90 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 ...
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1answer
50 views

Skin effect for a modified antenna with a high frequency pulsed DC

A direct current will be interrupted by a high frequency switch. It seems , that in a wire, connected to the source (the antenna rod), instead of pushed back- and forwards electrons, the electrons get ...
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1answer
83 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
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3answers
120 views

Reflection behaviour of the radiation as a function of the used voltage

According all the answers to a question about What is the advantage of making an antenna resonant different lengths of the antenna rod could be tuned to resonance with the antenna generator. You ...
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1answer
193 views

How do I understand this figure about antenna pattern? [closed]

Why the back lobes have such a large area??? I think it may be like https://www.cisco.com/c/dam/en/us/products/collateral/wireless/aironet-antennas-accessories/prod_white_paper0900aecd806a1a3e.doc/...

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