antenna-theory.com

[mx_ivanko]

I am a bit confused on how VSWR is related to S11 according to the pages provided on this site.

On one hand you have:

"The minimum VSWR is 1.0. In this case, no power is reflected from the antenna, which is ideal."

A VSWR of 1 translates to a reflection coefficient or S11 of 0, correct? So, why does the S11 page say:
"If S11=0 dB, then all the power is reflected from the antenna and nothing is radiated."

The S11 page even goes as far as making a graphical representation as to why a S11 of 0 is not good at all, which provides further confusion compared to the VSWR page.

Any insight as to why they seem conflicting, at least to me, would be of great help.

Max

[bigSteve]

You gotta watch your units

VSWR=1 is equivalent to s11=0 which is equivalent to s11=-infinity dB

So s11 is reflected power, and if it is zero, nothing is reflected. But 0 is -infinity decibels.

Now if s11 has a magnitude equal to 1, then everything is reflected. But if s11=1 in linear units is converted to dB, you get s11=0 dB.

See:

http://www.antenna-theory.com/definitions/decibels.php