[Antennas] Q loaded versus unloaded

2003年9月30日 20:03:55 -0400

Dear Juan,
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I'm in the process to understand in detail the basics of antenna theory and
matching lines (transmission lines) and I have arrived to a point where I
am a little bit confused:
Where could I find the difference between Q unloaded and loaded and their
effects in the antenna design?
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For an inductor (coil), in a theoretical analysis, the Q of the coil itself
should be high, of course, in order to minimize loss. Any loss in the coil
itself results in lower unloaded Q.
Once the inductor is "loaded" (a lossy element is placed in the same circuit
with the inductor), and a new Q is calculated based on that additional loss,
then the new value of Q is a function of the inductor's own losses and the
additional losses of the rest of the circuit. However, we now are talking
about the Q of the "circuit" - not just the Q of the inductor itself.
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According to what I understood if the Q of a coil in the antenna is very
high, the bandwidth decreases and losses too.
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That is reasonable and true.
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However in some articles
related to tuners I found that coils with low Q reduces losses and it's
better to use them ... is the "unloaded" versus "Loaded" present here?
Anyone could be so kind to clarify me this point.
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That makes no sense and I would appreciate a reference in order to
understand the context.
I believe there is a misunderstanding there.
Bob Lay (W9DMK) in Dahlgren, VA
http://www.qsl.net/w9dmk