UWB and WiMAX Antenna design _ Gain

[simotic]

Dear all,
i'm working on printed antenna design for UWB and WiMAX applications. the S11 obtained are more less than 10 dB (-30 dB for the first antenna, and -50dB for the second designed antenna), but the problem is that the gain of these antennas is less than zero (for the first antenna gain<-2dBi, and for the second gain<0)! so please can anyone explain this phenomena and how can i enhance the gain of the antenna.
To be noted that i use Rogers (Eps=3.38) as subsrate.
Thank you in advance
best regards.

 

[vfone]

0dB of gain for a wideband antenna with -50dB return loss (VSWR = 1:1.01) !!??
This is probably better than in your dreams.
Let like this, don’t touch anything, and go ahead for mass production.

 

[simotic]

Thanks dear freind for your reply,
please comments this figures.
on the other hand in my design the ground plane is slotted, so what effects if we want to integrate this antenna on PCB or Phone (when the ground plane will be totally covered). i'll be grateful for your help, thanks.
the size of the antenne is (X, Y, Z) = (10mm, 16mm, 0.83mm)



Thanks.

 

[vfone]

Make more sense now looking to the pictures. Actually you have a -10dB return loss (minimum) over the frequency range, and -6dB of gain (minimum) over the band.
The VSWR is right on the limit, but probably you need to do more work to improve the gain.
0dB over the frequency band is a good target for antenna gain.

 

[simotic]

ok dear vfone,
many thanks indeed for your prompt reply.
please how can i improuve the antenna gain? so what technics i have to do?
if you have documentation about this please to send it to me.
best regards.