Understanding Antenna efficiency

How to use openEMS. Discussion on examples, tutorials etc

Moderator: thorsten

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MPCEngineer
Posts: 31
Joined: Thu 02 Sep 2021, 18:29

Understanding Antenna efficiency

Post by MPCEngineer » Wed 29 Sep 2021, 11:51

Hi All,

On many example scripts the antenna efficiency is given as

disp( ['efficiency: nu_rad = ' num2str(100*nf2ff.Prad./P_in_0) ' %']);

where P_in_0 is the power in at the frequency of interest and calculated from port.P_acc accepted power.
nf2ff.Prad is the total radiated power from the antenna.

My questions are:
1) What decides the actual power level going into the simulation? when I run simulations I am getting levels as low as:
Accepted power P_in_0 = 9.7583e-28Watt
radiated power: Prad = 1.1931e-28 Watt
These seem very low power levels. Are such low levels correct? I assume they are derived from the initial Gaussian excitation is this correct?

2) Does the efficiency calculation include the mismatch between the lumped port and the antenna as well as the losses in the antenna?

3) I assume you have to ensure the frequency chosen is actually the resonant antenna frequency.

Many Thanks,

MPC

thorsten
Posts: 1475
Joined: Mon 27 Jun 2011, 12:26

Re: Understanding Antenna efficiency

Post by thorsten » Sun 03 Oct 2021, 19:01

1) yes this levels are (most likely) correct. Use the file "et" and converted to ef (frequency domain) no normalize out the effect of the excitation pulse amplitude.
2) That depends on what the script actually calculates. I'm usually only interested in the antenna efficiency only as fixing a mismatch is the task for a proper matching network. If you use P_acc (accepted power) it should be without matching.
3) Not necessarily, the antenna efficiency should not depend on it (at least if some energy got feed into the antenna after all)

br
Thorsten

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