and how to find the min power density for antenna sensitivity to recieve?
The power an antenna receives is proportional to its gain in that direction. The gain can be related to an effective area.
Gain = (4 pi effective area)/(wavelength squared). This means the power received by an antenna can be worked out from the effective area (using the gain in that direction) and the power density in watts/sq metre arriving from that direction.
There is no lower limit to the power an antenna can receive, until you get to quantum effects. The receiver has a noise level, and the signal will need to be above the noise for the receiver to see it. You will need to choose the gain of your antenna(s) to suit the available power or power density and the sensitivity of your receiver.
You can get the gain by doing a far-field calculation in CST.
If you have 2 antennas and you want to find out how much gets from one to the other, if they are in each other's far field, do far-field simulations to get the gains for both and use the Frijs equation. If they are in each other's near field then it is harder, but you may be able to do one simulation with both in (usually too big) or simulate one, replace it with its fields on a boundary, and use that to predict the other antenna.
Read an antenna book to find out about gain and effective area, and near- and far-fields. Look up the Frijs equation (some people think it's spelt Friis).
Advice from above correspondence is as good as u can get I think. However, the decision will ultimately depend on the accuracy u are looking for. Suggest you think about that before going further.
Hanieh Hojjatzadeh You can use a matched load at the receive antenna port and measure the current through it to determine actual received power.
Sensitivity is defined for the receiver and not the antenna. Malcolm White has elaborated on it already.
In CST a waveguide port acts as a matched load and measures received power, giving it in terms of the S-parameter.
Excellent & informative discussion! Congratulations!! & best wishes.
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