Can this image be confirmed valid, please ?

Thread Starter

Externet

Joined Nov 29, 2005
1,846
Hello all. Loop antennas directionality :

1649197230230.png


----> And, is that image for vertical polarization transmitting antennas ? <----
 

Ramussons

Joined May 3, 2013
1,262
Perpendicular or Horizontal makes no difference.
That figure and explanation is incorrect.
For a loop antenna, Maximum pickup is on Broadside, Minimum along the Plane of the loop.
 

Ya’akov

Joined Jan 27, 2019
5,657
Perpendicular or Horizontal makes no difference.
That figure and explanation is incorrect.
For a loop antenna, Maximum pickup is on Broadside, Minimum along the Plane of the loop.
@ericgibbs pointed out the radiation pattern of a loop but in addition the polarization is important as well. There are vertically and horizontally polarized loops though the radiation patters just stays relative to the polarization as you’d expect.

There are even circularly polarized loops.
 

Thread Starter

Externet

Joined Nov 29, 2005
1,846
Hi. Revisiting this subject, In post #1; did we agree that the wave polarization on the graphic was vertical ?


Is it safe to assume the circumference elements are loops for this television antenna below ?
1650820978418.png

Then, if television signals are horizontally polarized; why the above antenna is designed/mounted for vertical polarized signals ?

Television receiving antenna as for horizontal polarization as I always knew...
1650821962535.png


I have 3 TV antennas at home, 2 of them I built like the below one. Shouldn't a loop for television reception be mounted like :
1650822241994.png

LIGHT, please ?
 

Ya’akov

Joined Jan 27, 2019
5,657
As far as I can tell, despite the appearance this is not a loop antenna. You can see the horizontal dipole behind the "loops". The description says it is "multi-element", so something different is going on inside those radomes.

It is a very highly rated antenna, mostly considered the best dual band apparently.

I wonder if it is a variation of a bowtie antenna.
 

Ya’akov

Joined Jan 27, 2019
5,657
It seems that vertical and elliptical polarization is a thing for UHF DTV so by using the vertical polarization, the antenna is much more directional which could be the goal.

There are broadcast antennas that allow both vertical and horizontal transmission at the same time.
 

Tesla23

Joined May 10, 2009
510
Small loops (diameter << wavelength) are linearly polarized and have the radiation pattern shown by ericgibbs, with the direction of maximum radiation in the plane of the loop.

Larger loops (particularly resonant loops) are also linearly polarized and have a radiation pattern with a maximum perpendicular to the plane of the loop. This is likely the caase of the TV antenna shown, but without more details on the size, frequency, feeding mechanism, it's hard to say.
 

nsaspook

Joined Aug 27, 2009
9,722
As far as I can tell, despite the appearance this is not a loop antenna. You can see the horizontal dipole behind the "loops". The description says it is "multi-element", so something different is going on inside those radomes.

It is a very highly rated antenna, mostly considered the best dual band apparently.

I wonder if it is a variation of a bowtie antenna.
I agree with you, It's a UHF bowtie (type) antenna with a classic bow-tie reflector AND a VHF dipole.

 

Tesla23

Joined May 10, 2009
510
I agree with you, It's a UHF bowtie (type) antenna with a classic bow-tie reflector AND a VHF dipole.
If it was a bow tie it would be vertically polarized. I suspect it is approximately an array of resonant loops which, in that configuration, would be horizontally polarized.

The specs I've seen aren't that good, but it looks trendy. I suspect that simple arrays of bow ties would have better specs. So I think it is sold as a fashion statement rather than as a triumph of antenna engineering.

I've also seen this picture with VHF capability:
1650844878758.png

Whilst I'm no expert on US TV polarization conventions, my guess is that both UHF and VHF are horizontally polarized in that configuration.
 

nsaspook

Joined Aug 27, 2009
9,722
If it was a bow tie it would be vertically polarized. I suspect it is approximately an array of resonant loops which, in that configuration, would be horizontally polarized.

The specs I've seen aren't that good, but it looks trendy. I suspect that simple arrays of bow ties would have better specs. So I think it is sold as a fashion statement rather than as a triumph of antenna engineering.

I've also seen this picture with VHF capability:
View attachment 265768

Whilst I'm no expert on US TV polarization conventions, my guess is that both UHF and VHF are horizontally polarized in that configuration.
It could be a tapered loop.

1650851081973.png

It looks like a loop but functions more like a full wave dipole in the desired frequency band.
 
Last edited:

Thread Starter

Externet

Joined Nov 29, 2005
1,846
Thanks, nsaspook, good find. The text inside the loop mentions "dipole bent and joined" I believe refers to the two arrows and the line on top of the image. Have to suspect that if the line and arrows were not shown, it would make perfect sense as considering it as a single loop conductor.
Tried to find the patents unsucessfully myself to learn their rationale :( ----> https://www.antennasdirect.com/antennasdirect-patents.html
Cannot find the drawings :(----> https://patents.justia.com/patent/11024968 <---- the claim being ornamental !

If it was a bow tie it would be vertically polarized. I suspect it is approximately an array of resonant loops which, in that configuration, would be horizontally polarized.
Never knew that. Can you please direct me to any tutorial were I can learn about it ?
When you mention "resonant loop" at what frequency resonates ?

It's a UHF bowtie (type) antenna with a classic bow-tie reflector AND a VHF dipole.
A dipole receives efficiently at a frequency determined by its construction length; which whatever it is, does not cover 50 to 220 MHz. Cannot understand how a single non-telescopic VHF dipole is meant to receive 50MHz to 88MHz and 170MHz to 220MHz :(

Light, please.
 

nsaspook

Joined Aug 27, 2009
9,722
A dipole receives efficiently at a frequency determined by its construction length; which whatever it is, does not cover 50 to 220 MHz. Cannot understand how a single non-telescopic VHF dipole is meant to receive 50MHz to 88MHz and 170MHz to 220MHz :(

Light, please.
The key words are efficiently matched for power transfer. It's most efficient when matched at resonance but will work as a voltage source of a usable rf receiver signal over a much wider range.
 

Tesla23

Joined May 10, 2009
510
Never knew that. Can you please direct me to any tutorial were I can learn about it ?
When you mention "resonant loop" at what frequency resonates ?
Jasik - 'Antenna Engineering Handbook' - Chapter 5 in my edition. You can find it online.

This looks OK but I haven't studied it:
https://researchpapers4scolars.files.wordpress.com/2015/06/67827_05.pdf

The impedance data shown is standard:
1650926181305.png

where you can see the resonance when the circumference is about a wavelength, and if you make the loop fat it is more broadband.

When fed at the center of the top or bottom it is horizontally polarized as, along the loop's axis the radiation from the vertical currents (sides) cancel by symmetry, but, at resonance, the radiation from the horizontal currents (top/bottom) add.

One rough approximation is to take a folded half-wave dipole, this has a conductor length of a wavelength, and pull it apart in the middle.

Tapering will change the broadband nature, I suspect that at the higher frequencies the upper section dominates and so the fact that you lose the phasing with the bottom matters less. My gut still tells me you would be better with a bow-tie, but I haven't done any measurements/simulations.
 
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