Help me calculate antenna's EIRP

I have simulated an antenna and want to calculate its EIRP, Should i get it from the maximum E-filelds of 3D radiation pattern at diff frequencies, or from the E-filelds of certain direction? If latter, does it mean that the EIRP of antenna is directional?

On the other hand, how can i get EIRP in measurement? from the pulse in time domain? So it will relate to the direction?

Thanks!

EIRP(Effective isotropically-radiated power) is not quite a characteristic of antenna

Take a look here http://en.wikipedia.org/wiki/Effecti...radiated_power

Uh, yeah. If you have 1 watt of transmit power at the coax connector, and you connect it to a 30 dB gain antenna, then you have 1 KW of EIRP in the main beam.

so does it mean that EIRP of antenna is the Gain*inputPower, if the inpuPower is fixed, the EIRP is only related to the gain at diff. frequecny?

In general all correct. Only the field is computed in a distant area, therefore often in a formula is inserted the losses on a canal track.

Yeah, the gain * power is EIRP. But remember that antenna gain often changes drastically with where you are pointing it! ie the gain is directional.

I'm a little confused, so Gain here is not the (maximum directivity)*eff, but is diff. from the direction: directivity(theta,phi)*eff. ?