Why i got the test different S11 with different ground?

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John_li

Joined: 06 Aug 2005
Posts: 210
Helped: 8

28 Aug 2008 0:06 Why i got the test different S11 with different ground?

Hi all,
I measured 5.8G helix antenna(S11 parameter) soldered with different gounds as photoes.And I got the different results,i do not know what cause the different results,anyone can help me?

Thank you

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FvM

Joined: 22 Jan 2008
Posts: 5177
Helped: 768
Location: Bochum, Germany

28 Aug 2008 11:09 Why i got the test different S11 with different ground?

At 5.8 GHz, your feeding cable to PCB interface can be expected to have already a considerable reflection coefficient. It can't be identical for the three cases.

The cable position also affects the antenna impedance to some extent.

Generally, the effects could be better understood from a S11 frequency sweep, it would reveal e. g. resonances.