Conversions between electric field strength (E), magnetic field strength (H) and power density (S).

E = Z_0 H                 S = E^2 / Z_0 = Z_0 H^2                 Z_0 = 120 pi = 377 Ohm
Electic fiels strength:E = V/m
Magnetic field stregth:H = A/m
Power density:S = W/m2

Enter one value (either E, H or S) and click the "Convert" button next to it to compute the two other values.

In the far-field region the electric field is normal to the magnetic field, they are both normal to the direction of radiation and they are in phase. Under these conditions the power density, the electric field and the magnetic field are related with simple relations involving the impedance of vacuum Z0.

Conversions between frequency (f), wavelength (lambda) and equivalent antenna area (Ae).

f = c_0 / lambda                 A_e = g * lambda^2 / (4 pi)                 c_0 = 3 * 10^8 m/s
Frequency:f = Hz
Wavelength:lambda = m
Antenna gain:G = dBi
Equivalent area:Ae = m2

Enter the gain G and one value (either f, lambda or Ae) and click the "Convert" button next to it to compute the two other values.

The equivalent area of an antenna is used to describe its power capturing characteristic when a wave impinges on it. It isn't a "physical" area of some part of the antenna, it's just a figure that has the dimension of an area [m2].

Conversions between received power (Pr), equivalent antenna area (Ae) and power density (S).

P_r = A_e S
Power density:S = W/m2
Equivalent area:Ae = m2
Received power:Pr = W

Enter two values (between S, Ae and Pr) and click the "Calculate" button next to the missing one to compute it.

Once we have the equivalent area and the power density of an incoming electromagnetic field, we can calculate the received power at the access, when the impedance is matched.

Remark: the equivalent area depends on the direction of the incoming wave.

Bibliography:

C.-A. Balanis, Antenna theory, analysis and design Wiley, 1997, Chapter 2.

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