Importance of S11 in antenna design

[yasine79]

Hi All,
I am designing an antenna, wich will be used in water. I tried to optimze the matching of the antennas(transmitter and receiver antennas), but with no success (S11=-3db) . I am just interested in S21. S21 is good enough for me to do the measurement.

Is it bad to devolop this antenna just according to its S11? or ist enough to have the optimal Transmisssion S21?


Thank you all

 

[rube]

Can you upload your project, thanks!

 

[FvM]

Water is a lossy medium, so a good S11 number isn't necessarily related to efficient antenna operation. Of course, you should still try to match the transmitter to a given antenna impedance.

 

[yasine79]

Thank you for ur answer!

When you want to design for exemple a horn antenna, which will be used in free space, the matching (S11) should be good in free space for the wanted frequency band. My goal is to design an antenna which should show a good matching in water. So it do es not matter how lossy the water is.

or not?

thank u

 

[volker@muehlhaus]

I am just interested in S21. S21 is good enough for me to do the measurement.

The difficulty is that such bad S11 also changes S21, because if half the power is reflected by the antenna, that part is missing in the signal path. No problem if your S11 is bad, but constant for magnitude and phase. If it changes, then you will see a change in S21 also.