# Can we apply Friss equation to find field strength at the receiving point...

1. Jan 8, 2016

### aashna

Can we apply friss equation to find field strength at the receiving point for space wave propagation?

2. Jan 9, 2016

### tech99

The Friss formula gives the path loss between two antennas of specified aperture when in free space, so it does not directly give the field strength. The easiest formula for radiation from a dipole in free space is: E = (7* sqrt p / d^2 ) in volts per metre, volts, metres, watts.
The formula is not applicable for propagation over ground.You can introduce factors for gain and ground reflection if required. Be careful if a monopole antenna.

3. Jan 9, 2016

### aashna

thank you!
but sir friss equation can easily give us the power received by the antenna and we know the relation between power,poyenting vector ,and electric field. power_received=poyenting_vector*effective_aprerture and poyenting_vector=(electric_field)^2*η. So now can we calulate electrc field?. The mode of propagation is space wave.

4. Jan 9, 2016

### tech99

Agree, but you asked if the Friss formula gave field strength. The formula I have given seems to be quite simple.

5. Jan 10, 2016

yeah!
i like it.