about loaded microstrip antenna

i have disigned a loaded microstrip antenna using IE3D9.3.i find impedance matching is easy to achieve,but the GAIN is very low!
and it is not like what some papers said.
who can help me?
is there any other EDA software can simulate the loaded microstrip antenna?
thanks.

Your observation is fully correct. Gain reduces due to power dissipation in the load. Remember the BW of a 50 Ohm resistor is Infinity but radiation efficiency is Zero.

radiation efficiency is Zero？
is it said that this loaded antenna is no use?

Hi dragonlea,

the radiation efficiency of the resistor is zero, not of the loaded antenna.
But because of the load, the efficiency of the whole antenna will get worse.
To say now, this antenna is useless is wrong. You have many advantages
of your loaded antenna. This could be the higher bandwidth and so on.

Bye

loaded microstrip antenna can be simulated also using Ensemble, HFSS, or Ansoft designer

Hi,

The radiation and mismatch (reflection) efficiency of a common loaded microstrip antenna is low because it is very close to a ground plane. This causes the combining interference of in-phase & nearly-out-of phase fields (depending on substrate height vs. frequency). This field combination emanates from the same antenna plane resulting in very weak field intensity.
Now, the low mismatch efficiency problem can be solved by the load you use - which is fine, however, the electric field intensity remains low.

Regarding EDA - CST Microwave Studio can also simulate such antennas

Rgdz,
p.

Hi, Dragonea:

IE3D is excellent for loaded microstrip antennas. If the radiation efficiency of the matched anenna is low, it is quite likely due to metallic loss or surface wave loss. You may want to revise your structure. A simple example with such a case is a PIFA antenna with the shorting pin very close to the probe. When the shorting pin is very close to the probe, you may be able to achieve a deepresonance with good match at low frequency when the structure can be smaller than lambda/4. However, the radiation efficiency is normally very low because deep resonance is caused more by the metallic loss instead of radiation loss. When such case happens, you may need to revise your structure and try to improve the radiation efficiency. Regards.