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comanchero
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admin
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 Posted: Sun Jul 19, 2020 10:35 pm Post subject: |
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| I haven't heard of it before. What are the advantages or why do you have interest in this particular antenna? |
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R. Fry
Antenna Theory Regular
Joined: 06 Jun 2011
Posts: 49
Location: Illinois USA
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| Posted: Tue Jul 21, 2020 9:20 am Post subject: Re: Lindenblad antenna |
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| comanchero wrote: | | ... I could not find anything - neither on the website, nor in the forum - on this specific and interesting antenna type/configuration. ... Could, possibly, some of the AT's authors write/explain the theory?... |
The radiation pattern of a properly-driven Lindenblad antenna is circularly polarized with a very low axial ratio. That is, its free-space, radiated fields are nearly uniform in all planes of polarization.
The benefits of that are:
1. The physical orientation of receive antennas is less important, and
2. Reflections of the radiated wave as a result of the propagation environment tend to be rejected by a receive antenna with the same sense of rotation as the transmitted waveform.
Below is a link to a graphic showing the radiation envelope calculated by NEC4.2 from/for a Lindenblad antenna in free space.
https://i.postimg.cc/7bvXpCB5/Lindenblad-Radiation-Envelope-Free-Space.jpg |
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comanchero
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Joined: 10 Jul 2020
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| Posted: Sun Aug 02, 2020 10:03 am Post subject: VHF/FM Broadcast |
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| admin wrote: | | I haven't heard of it before. What are the advantages or why do you have interest in this particular antenna? |
Hello, @admin,
my main scope of interest is VHF/FM Broadcast.
The main advantage is that it is very likely the only Circularly polarised antenna with perfectly Omnidirectional radiation pattern (as @R. Fry also mentioned).
https://en.wikipedia.org/wiki/Circular_polarization#FM_radio
https://en.wikipedia.org/wiki/Omnidirectional_antenna
The other, more popular C pol. solutions will never be perfectly 360° radiating, due to the shade and reflections of the mounting pole.
https://www.aldena.it/wp-content/uploads/2020/03/acg010223x-vhf-band-ii-fm_aldena.pdf
https://www.aldena.it/wp-content/uploads/2020/03/acf02022xx-vhf-band-ii-fm_aldena.pdf
The probably only other way of achieving 360° radiation is horizontally stacking directional C pol. antennae.
https://www.aldena.it/wp-content/uploads/2020/03/alp050291x-vhf-band-ii-fm_aldena.pdf
https://www.aldena.it/wp-content/uploads/2020/03/APX02025x0-VHF-Band-II-FM_Aldena.pdf
https://www.aldena.it/wp-content/uploads/2020/03/aqp0402420-vhf-band-ii-fm_aldena.pdf
This solution though loads the budget significantly - possibly making it unavailable to many local LPFM broadcasters.
The main disadvantage of Lindenblad probably is its possible attraction to lightnings. Thus a lightning rod must be mounted on top of the mounting pole, sharing the platform with the antenna - to be placed above the antenna in order to be a higher leading point (in the area).
And that might concern me mostly. What do you think - is it possible to effectively/perfectly de-couple the lightning rod from the antenna, to by 100 % prevent the lightning from "jumping over" into the antenna (which then would lead it back into the transmitter)
Here one more product:
Amphenol Procom (VHF/FM Broadcast)
https://amphenolprocom.com/products/base-station-antennas/2381-lblad-600
I though still am very interested in the theory: How do the dipoles interact with each other, creating a perfectly omnidirectional circularly polarised signal, without distracting each other? (There still is a rod between them, too.) Do you see a potential for an article (on the topic)? 
THANKS.
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comanchero
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| Posted: Sun Aug 02, 2020 10:11 am Post subject: Re: Lindenblad antenna |
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Hi, @R. Fry,
yeah, THANKS for the info. I still am very interested in the INTERACTION between the dipoles - HOW they create the UNIFORM omnidirectionally radiated circularly polarised signal.
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R. Fry
Antenna Theory Regular
Joined: 06 Jun 2011
Posts: 49
Location: Illinois USA
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| Posted: Sun Aug 02, 2020 11:31 am Post subject: Re: VHF/FM Broadcast |
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| comanchero wrote: | | ... What do you think - is it possible to effectively/perfectly de-couple the lightning rod from the antenna, to by 100 % prevent the lightning from "jumping over" into the antenna (which then would lead it back into the transmitter) ... |
No practical antenna can "100% prevent" damage to itself and anything connected to it from a direct strike by lightning.
However the metallic components of some antenna designs have a very low-resistance path for direct current and low-frequency alternating current between the two terminals of their input connector. Normally the shield of a coaxial cable between the antenna and transmitter is "grounded" at the transmitter, through the safety ground path of the incoming a-c mains service. This can reduce the static voltages that may build up on elements of the antenna, which makes the antenna less likely to attract lightning to strike it.
One example of such an antenna design is the Amphenol Procom LBLAD-600, which includes this text in the link you provided to it: "All metal parts DC-grounded (Connector shows a DC-short)."
| Quote: | | I still am very interested in the INTERACTION between the dipoles - HOW they create the UNIFORM omnidirectionally radiated circularly polarised signal. |
The short answer lies in the physical spacing, angular orientations, and r-f currents/phases used to drive each of its elements.
The long answer is found in antenna engineering textbooks.  |
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comanchero
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