Most sensitive part of antenna? - RF Cafe Forums

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James King

Post subject: Most sensitive part of antenna?

Posted: Fri Jun 20, 2008 9:02 pm

Lieutenant

Joined: Sun Aug 31, 2003 3:20 pm
Posts: 3
Location: Midwest

If I have say a 2.4 GHz 1/4-wave antenna mounted on a metal case and need to attach a metal clip-on thingy to it (a small plastic flag with a metal clip), is it least intrusive to attach it at the bottom, middle top? Please exlpain in your answer why you say so. Thanks guys.

JK

nubbage

Post subject:

Posted: Mon Jun 23, 2008 6:39 am

General

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK

Hi James
A quarter wave antenna with a low impedance at the equipment end, normally 50 ohms, will have a high impedance a quarter wave away ie at the outer end.
High impedance parts of an antenna are always the most sensitive to nearby metal object, because capacitive coupling occurs at these points even due to very small stray capacitance, as in the case of a metal clip.
A teflon or better a foam plastic clip, would probably have least impact on performance. A metal clip would be disastrous, IMHO.

nubbage

Post subject:

Posted: Mon Jun 23, 2008 6:42 am

General

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK

As usual, I read the question after giving the answer.
A metal clip could be placed at the base of the antenna if it is small compared to the quarter wavelength.
Neither the top nor the middle would be wise.

Posted 11/12/2012