Another Hfss simulation problem

[lydu]

Hi,

I have send a topic about antenna Directivity/Gain.Then i tried to look for the cause,another problem occur.
Case1: frequcy = 2GHz, Caculation result is
VSWR=1.71
Antenna Gain = -1.882dB
Antenna Efficiency =0.96121
Case2: frequcy = 3GHz, Caculation result is
VSWR=2.63
Antenna Gain = -0.5314dB
Radiation(?=Antenna) Efficiency =0.58621
Why the match is more better,the Gain is the worse.The result let me faint.
My god! what's wrong?
The detail simulator file is in attachment

 

[lydu]

Sorry, Suplement the Hfss file

 

[asdfaaa]

Why the match is more better,the Gain is the worse.The result let me faint.
My ---! what's wrong?

Impedance matching is just to get more energy into the antenna, while Gain is productor of Directivity with Radiation Efficiency, there is no such relationship between impedance matching and Gain: better impedance match, higher gain.
You may find the Balanis' book "antenna theory" Chapter 2 to find out more details.
Impedance bandwith is one requirement of placement antenna into full system to get optimal performance, while radiation pattern (directivity, gain) is also design requirement from antenna itself point of view.

Regards,

 

[lydu]

Hi,asdfaaa

Thanks for you replay,but the "bad matching + low Radiation Efficiency -> higher gain" lets me faint. Could you try the attchment model?
another question, why Gain <-1dB for the antenna of Radiation Efficiency 0.96 and VSWR 1.6. where is the energy ?

lydu

 

[jallem]

I had the same problem before. The efficiency
is just the ratio between the radiated power and the
accepted power. And the return los is the ratio between
incident power and the accepted power. So, I do is looking
to antenna parameter table, Ex:
1) Peak Directivity = 7.6
Peak Gain = 7.79
Peak Realized Gan = 6.05
Radiated Power = 28.58 dBm
Accepted Power 28.25 dBm
Incident Power = 30 dBm
Efficeincy = 1.0785

Notice the eff is larger than one. I dont worry too much
since that depend on the air box to calculate the radiated
power. There is however a discussion about eff ≥ 1 in this
forum. If the difference between the peak directivity and
peak gain versus radiated power and accepted power is almost
the same then I dont worry. I know the antenna is radiating.
I believe the difference in the near field. If those two number
are too difference then the antenna is not "radiating" but
produce more near field energy that does not reach the radiation
boundary.