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Will
Antenna-Theory.com Newbie
Joined: 08 Jul 2014
Posts: 2
Location: Cambridge UK
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 Posted: Tue Jul 08, 2014 3:46 pm Post subject: Monopole electric field strength? |
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I have a text book that gives the following approximation for the far-field electric field strength for a monopole antenna - is this a reasonable approximation?
E = 4 x Pi x 10^-7 x f x I x Len/R
f = frequency
I = current
Len = length of the monopole
R = Distance from antenna |
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mkiv
Antenna-Theory.com Newbie
Joined: 09 Jul 2014
Posts: 4
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| Posted: Wed Jul 09, 2014 7:11 am Post subject: |
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I have never come across that equation, but that doesn't mean its incorrect.
The way I derive E-field in the far field is by using the free space path loss.
S = PG/(4xPIxr^2) [W/m^2]
S = ExH [W/m^2]
= E^2/Z (for plane waves in free space)
Z = 120xPI [ohms]
therefore
E = sqrt(PGZ/(4xPIxr^2)) [V/m]
Last edited by mkiv on Wed Jul 09, 2014 7:20 am; edited 1 time in total |
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Will
Antenna-Theory.com Newbie
Joined: 08 Jul 2014
Posts: 2
Location: Cambridge UK
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| Posted: Wed Jul 09, 2014 8:08 am Post subject: |
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| mkiv wrote: | I have never come across that equation, but that doesn't mean its incorrect.
The way I derive E-field in the far field is by using the free space path loss.
S = PG/(4xPIxr^2) [W/m^2]
S = ExH [W/m^2]
= E^2/Z (for plane waves in free space)
Z = 120xPI [ohms]
therefore
E = sqrt(PGZ/(4xPIxr^2)) [V/m] |
I must admit I am new to this antenna stuff, my motivation is in understanding EMI, specifically unintentional radiated emissions caused by common mode currents on cables connected to electronics products.
I can measure these currents using a high frequency clamp on current probe - I would like some form of closed form approximation to the far-field electric field strength relating to this measured current, the length of the cable and the frequency. The equation in my original post claims to give this, I was just wondering if it seemed reasonable to the 'Antenna experts' on this forum? |
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