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Old August 6th 17, 12:17 PM
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Post Ohmic losses- not microstrip.

Hello all. If we assume that the antenna's surrounding is air, then my assumption is that dielectric losses for the antenna are rather negligible. What type of antennas are usually showing higher effect of ohmic losses?
I mean, I know that reflector antennas are usually little susceptible to ohmic losses. But some types are not, my assumption would be loop antennae,
Another thing is attenuation in waveguides. I assume that it would be the case with many tens of GHZ, for rectangular device. But, as I am only guessing, as I have been out of the game for long.

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Old August 6th 17, 05:31 PM posted to rec.radio.amateur.antenna
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Default Ohmic losses- not microstrip.

ldagan wrote on 8/6/2017 7:17 AM:
Hello all. If we assume that the antenna's surrounding is air, then my
assumption is that dielectric losses for the antenna are rather
negligible. What type of antennas are usually showing higher effect of
ohmic losses?
I mean, I know that reflector antennas are usually little susceptible to
ohmic losses. But some types are not, my assumption would be loop
antennae,
Another thing is attenuation in waveguides. I assume that it would be
the case with many tens of GHZ, for rectangular device. But, as I am
only guessing, as I have been out of the game for long.


Small loop antenna work with large currents and so suffer from ohmic losses
more than many other types.

--

Rick C
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Old August 6th 17, 06:40 PM
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Thumbs up That is not what I was looking for, exactly

first of all, thanks.
I mean, yes, currents are higher, but I was talking in relative terms, not absolute terms. I mean, reflectors and horn antennas can send very strong currents, or are you referring to high current density?
-Lior
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Old August 6th 17, 10:39 PM posted to rec.radio.amateur.antenna
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Default Ohmic losses- not microstrip.

ldagan wrote on 8/6/2017 1:40 PM:
first of all, thanks.
I mean, yes, currents are higher, but I was talking in relative terms,
not absolute terms. I mean, reflectors and horn antennas can send very
strong currents, or are you referring to high current density?


The current density depends on your design. If you use a very small
conductor for a loop the density will be higher than if you use a large
conductor. But in both cases the current in the conductor will be much
higher than in many other antenna types.

--

Rick C
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Old August 7th 17, 12:20 AM posted to rec.radio.amateur.antenna
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Default Ohmic losses- not microstrip.

On Sun, 6 Aug 2017 12:17:16 +0100, ldagan
wrote:


Hello all. If we assume that the antenna's surrounding is air, then my
assumption is that dielectric losses for the antenna are rather
negligible. What type of antennas are usually showing higher effect of
ohmic losses?
I mean, I know that reflector antennas are usually little susceptible to
ohmic losses. But some types are not, my assumption would be loop
antennae,


Yes, loop antennas can be VERY sensitive to resistive losses thanks to
very high currents through the loop. The SLA (small loop antenna)
magnetic loop performance is highly dependent on having the highest
possible Q (to a limit where it becomes less than the modulation
bandwidth). Any series resistance would ruin the Q which is why
mechanical joints are soldered or brazed. Try playing with the AA5TB
SLA spreadsheet calculator at:
http://www.aa5tb.com/aa5tb_loop_v1.22a.xls
and watch what happens at low frequencies to the efficiency when you
increase the "added loss resistance". Notice that it's in milliohms.

Another thing is attenuation in waveguides. I assume that it would be
the case with many tens of GHZ, for rectangular device. But, as I am
only guessing, as I have been out of the game for long.


At GHZ frequencies, the skin depth is quite shallow. Therefore, only
the inside surface plating really needs to be low resistance. I've
worked with silver plated rigid molded PLASTIC WR90 X band waveguide
which worked but had mechanical rigidity problems. We also had
problems with cracked plating on outside 90 degree corners, such as on
flange to waveguide connections.

https://www.microwaves101.com/encyclopedias/waveguide-construction
http://www.eenewsautomotive.com/news/plastic-waveguides-future-communication-networks

--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


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Old August 7th 17, 02:27 AM posted to rec.radio.amateur.antenna
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Default Ohmic losses- not microstrip.

Jeff Liebermann wrote on 8/6/2017 7:20 PM:
On Sun, 6 Aug 2017 12:17:16 +0100, ldagan
wrote:

Another thing is attenuation in waveguides. I assume that it would be
the case with many tens of GHZ, for rectangular device. But, as I am
only guessing, as I have been out of the game for long.


At GHZ frequencies, the skin depth is quite shallow. Therefore, only
the inside surface plating really needs to be low resistance. I've
worked with silver plated rigid molded PLASTIC WR90 X band waveguide
which worked but had mechanical rigidity problems. We also had
problems with cracked plating on outside 90 degree corners, such as on
flange to waveguide connections.

https://www.microwaves101.com/encyclopedias/waveguide-construction
http://www.eenewsautomotive.com/news/plastic-waveguides-future-communication-networks


Silver is only some 10% better conductivity than copper and you lose about
half that back due to the skin effect. So in reality it is only around 5%
more effective (unless I'm remembering the numbers wrong and it's actually
20 and 10 per cent).

From what I've read a much larger effect is surface roughness at the really
high frequencies. If the roughness is comparable to the skin effect depth
it creates a longer, more resistive path.

--

Rick C


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