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Total Source Power for multiple Antennas

Altair Forum User

Hi,

I am modelling multiple monopole antennas on a structure. Each have their own power amplifier:

Monopole 1: 100W

Monopole 2: 100W

Monopole 3: 200W

Monopole 4: 250W

So, in my Source/Load tab, for Power, do I just sum these up to 650W? The user manual suggests this:

Total source power: If Total source power is selected, FEKO will scale the results such that the total source power (the sum of the power delivered by all the individual sources in a model with multiple sources) is equal to the amount speciﬁed in the Source power ﬁeld. No mismatch is taken into account. This option can be used with any source except plane waves.

Or is there a way to individually assign these powers to the Voltage sources?

Thanks,

Shashank

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Mel

Hi Shawshank

Scaling the power as you suggested will not set the individual monopoles' power to your requirements, but only the sum of the all powers.

If there is strong mutual coupling between the antennas then it is a bit tricky. For this case you would need to calculate the S-parameters and solve a set of quadratic equations to get the source amplitudes assuming the relative source phases between the antennas. This is not straightforward and will have multiple solutions. I don't have any further expertise on this case.

However, if you want to specify the available (forward) power (P_available) then you can load each port with the source resistance (Rs) and calculate and set the source voltage as Vs = sqrt(8*Rs*Pa). Then each antenna will radiate P_available when each antenna is matched to the source impedance.

Assuming that mutual coupling is small then you can scale each source voltage:

|Vs| = |Za|*sqrt(2*Ps/Ra)

where Za is the complex antenna input impedance, Ra = Re{Za}, and Ps is the required power level.

Altair Forum User

Hi Mel,

Thanks for the response. The multiple solutions by solving the s-parameters and quadratic equations sounds complex.

I'm more inclined to follow this:

However, if you want to specify the available (forward) power (P_available) then you can load each port with the source resistance (Rs) and calculate and set the source voltage as Vs = sqrt(8*Rs*Pa). Then each antenna will radiate P_available when each antenna is matched to the source impedance.

In your formula;

Vs = sqrt(8*Rs*Pa);

Pa is the P_available

I'm wondering where did the 8 come from? Please excuse my ignorance.

I was thinking of applying the source voltage to Sqrt (Power * Resistance) for each antenna.

Thanks much.

Mel

Hi Shashank

Voltages and currents in FEKO are peak values. But power is average power.

So let's assume a simple circuit representation of the source, the source resistance and antenna resistance. The source has a voltage set to Vs (which is peak).

Assuming the antenna is matched to the source resistance, then the antenna resistance and source resistance will get equal voltage drops over them.

So each resistance gets a (Vs/sqrt(2))/2 average voltage drop over them.

The average power then over the source resistance (or the antenna resistance) is:

P=(Vs/(2*sqrt(2)))^2/R

From there then if you work out Vs the factor 8 pops out.

Altair Forum User

Hi Mel,

Thanks for the explanation, appreciate it /emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />

Will try setting voltage sources to this - in a multiple sources scenario.

Thanks,

Shashank