Need GURU to check on my design. Thanks in advance!

Msg 1:
Dear All,

I am Alex from Malaysia. I have design a Dual-Band Antenna, however, it do give me a NEGATIVE gain graph. Any comment on the NEGATIVE gain, is it a BAD design? Anyone here have idea on how to improve it.

Thanks a lot, have a nice day.

Msg 2:
Dear All,

Good day to you all. I have try several ways to improve my gain, however, it still fall in the NEGATIVE region for my desired frequency. I want to ask, if anyone here can accord help to help me check on my design. I will send my HFSS file if anyone there willing to help to solve my problems.

Thanks in advance. May god bless you all.
:D

Negative gain (I am assuming it is in dB ) means that your structure has too much losses and/or very badly matched. But if you mean a negative gain at certain direction, this is normal, you should get positive gain at some angles and a negative gain at other angles even if you have a good design.

BR
Adel

Dear adel_48, thanks for reply and your comments take noted. For my design, i have positive gain in the frequency i doesn't want, but in the frequency i desired, it show negative. May i know how to improve the losses/very badly matched problem. Any simple example on it? Thanks a lot again...

Adjsust the dimensions (length) to work on your desired frequency. I guess you probably made the antenna too small for the frequency. Please start with a simple dipole antenna which will give you clear ideas about relationship between resonant frequency and dipole length.
S. H.

Dear shwoo, noted your comment, will work out on it. Thanks.

Negative gain relative to what? This could indicate a problem or it may just be an artifact of the way you are making your measurement. Another possibility is that you are cross polarized in the measurement.

What is s11?

How big is the antenna and where does it operate in frequency?

@Alex2202
If you are talking about simulation results,it might be due to simulation software(check you structure carefully) Usually at resonances the losses are not much.
Gain is relatively small if one use substrate of high permittivity and thick substrate.

Thanks for all the comments...All your valuable comments are noted down. I will try to troubleshoot it, thanks anyway. May god bless you all.