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printed antenna - RF Cafe Forums
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rf_sd77
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Post subject: printed antenna
Posted: Fri Jun 11, 2004 2:23 pm
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Joined: Fri Jun 11, 2004
2:17 pm Posts: 5 |
I am fairly new into antenna design as I have been
mainly a RF guy for 4 years working on TX and RX
circuits for cellular products and have ventured
into the 2.4GHZ area now. Question is I
am trying to figure out the main advantages of having
an antenna at 200ohms versus a 50ohm for 2.4Ghz.
From the tx or rx path I have a balun that converts
the signal from 50ohm to 200ohm (this is from previous
designer who left and i took over and he is overi
n japan now). I have worked with cellular antenna
and have always matched to 50ohms, just curiuos
why for a 2.4GHz antenna it would be 200ohms.
any insight on starting this desing would be
greatful as I am the only RF guy here and I am getting
some antenna design books next week. Thanks for
responses.
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K5DVW |
Post subject:
Posted: Fri Jun 11, 2004 2:51 pm
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The only reason that I can come up with is... that
impedance (200 ohms) is just what that specific
antenna type looks like. As you know, not all antennas
are 50 ohms driving impedance, infact most arent,
so you have to match to them. It just turns out
that some standard kinds of antennas, like monopoles
have a pretty low impedance to start with and can
be used in 50 ohm systems without matching. Some
patch antennas can look like 200 ohms due to the
physics of the antenna. In other words,
there is no advantage to having a 200 ohm termination
impedance specifically, but the antenna impedance
is more driven by the type antenna and what kind
of performance you need from an antenna pattern
point of view. Matching is often secondary.
If you have a resistive 200 ohms, then consider
yourself lucky, that's an easy match. Good
luck, Darrin
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rf_sd77 |
Post subject: thanks
Posted: Fri Jun 11, 2004 5:50 pm
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Joined: Fri Jun 11, 2004
2:17 pm Posts: 5 |
thanks for the insight, I had the feeling that was
the reasoning, just was not sure. I appreciate
the quick response.
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Chris |
Post subject:
Posted: Wed Jul 07, 2004 3:05 pm
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Also, just to add to the excellent comments, most
antennas if not all, have reactance so the actaul
impedance you are considering needs to take into
account R + jX for matching to your system or calculating
radiated power. If X is not minimized then radiated
power is reduced. Of course there are other variables
to consider in antenna design.
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Posted 11/12/2012
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