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Doubts regarding antenna propogation theory

 
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TheArun
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Joined: 13 Apr 2016
Posts: 2
Location: India

PostPosted: Wed Apr 13, 2016 7:00 am    Post subject: Doubts regarding antenna propogation theory Reply with quote

I have a few doubts regarding antenna radiation and propogation. Kindly look into it and clarify.

Consider a Hertzian dipole antenna,

DOUBT # 1. Generally, when the power is mentioned for an antenna elements such as the power dissipated across radiation resistance(Rrad)

P radiated = (1/2)I2Rrad

Doubt:
1. Generally, Power equation is P = I2Resistance, but according to the above equation only 1/2 of the power across the radiation resistance is actually radiated. Is it a case of power lost and where?
2. Does the half term come from the equation of power across load allowing ac power i.e.,

P = Vrms * Irms cos@

By taking the peak value of V and I and denoting V in terms of I it changes to, P = (1/2)I2R. If that is the case does that mean that,
a) Current, without mentioning explicitly is always considered to be an 'ac current peak value which is in phase with voltage'
and
b) If that is the case, does that also mean that Hertzian dipole or a current element that radiates as an antenna can only be made using a ac current and not dc current?

DOUBT#2: Consider a electric field having θ and φ component i.e.,
E = Eθ aθ + Eφ aφ
where,
E - electric field vector
Eθ - electric field component in θ direction and Eφ - Electric field compo in φ direction

So my doubt is what actually is this Eθ(or Eφ) which is a scalor along θ direction:
Is it a angle in θ direction ie say 30 deg in θ direction OR is it a distance?
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TheArun
Antenna-Theory.com Newbie


Joined: 13 Apr 2016
Posts: 2
Location: India

PostPosted: Wed Apr 13, 2016 7:17 am    Post subject: Reply with quote

Sorry for the unformatted equations. But i coudnt find the way a particular character can be sub scripted or superscripted. How is it done here?

The '2' in the above equatons means 'square' btw.
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admin
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Joined: 03 Jan 2007
Posts: 201

PostPosted: Fri Apr 15, 2016 12:21 am    Post subject: Reply with quote

Yes, the 1/2 term is because I is peak current. There is no lost energy.

A dc current will not radiate an electromagnetic wave. That's electrostatics, no propagation.

For your spherical coordinates questions, you'll have to brush up your spherical coordinates, spend some time with a math textbook.
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