- #1

Bobymayor

- 4

- 2

Hello everyone,

I was asking myself about electric field strength estimation at a distance d from - in my case - a half wave dipole antenna.

There are pretty much a lot of information about this on internet or in books but still, there are a few things that are confusing to me that I would like you guys to help me out !

"Settings" :

- Frequency F = 2GHz

- wavelength Wv = 150 mm

- Length of antenna L = 71,25 mm (0.475*Wv)

- Feeder impedance 73 ohms

- Power input = 1W

It is said that for a halfwave dipole antenna, Electric field strength can be calculated from an approximation (in the case where d is orthogonal to L) which is :

I already have a problem here, isn't the electric field strengh supposed to decrease with square distance in far field, (and cube distance in near field) ??

Another source here (okay I admit, Wiki but I guess it's reliable sometimes) gives the following equation regarding radiated power :

Which again is decreasing proportionaly !

I simulated in an EM analysis software (CST) this half wave dipole antenna following standard design rules and same parameters (and in the void) and it works pretty accurately at 2 GHz. Plotting the E strength along the distance, from the antenna to 1000 mm (several times Wv), we can see the shape here :

If we zoom into remove the peak around 0 :

And even more :

I don't even know what to think about this shape anymore... !

There may be something obvious I missed ? These formulas are very big approximation because it's impossible to estimate it ? If you could enlighten me I would be very glad !

I was asking myself about electric field strength estimation at a distance d from - in my case - a half wave dipole antenna.

There are pretty much a lot of information about this on internet or in books but still, there are a few things that are confusing to me that I would like you guys to help me out !

"Settings" :

- Frequency F = 2GHz

- wavelength Wv = 150 mm

- Length of antenna L = 71,25 mm (0.475*Wv)

- Feeder impedance 73 ohms

- Power input = 1W

It is said that for a halfwave dipole antenna, Electric field strength can be calculated from an approximation (in the case where d is orthogonal to L) which is :

I already have a problem here, isn't the electric field strengh supposed to decrease with square distance in far field, (and cube distance in near field) ??

Another source here (okay I admit, Wiki but I guess it's reliable sometimes) gives the following equation regarding radiated power :

Which again is decreasing proportionaly !

I simulated in an EM analysis software (CST) this half wave dipole antenna following standard design rules and same parameters (and in the void) and it works pretty accurately at 2 GHz. Plotting the E strength along the distance, from the antenna to 1000 mm (several times Wv), we can see the shape here :

If we zoom into remove the peak around 0 :

And even more :

I don't even know what to think about this shape anymore... !

There may be something obvious I missed ? These formulas are very big approximation because it's impossible to estimate it ? If you could enlighten me I would be very glad !