Power Divider
If the power divider is under matched condition then low wattage resistor is sufficient as there is no current flowing through this resistor.
Unless it is used as a power combiner, then half the power is dissipated in the resistor and half is delivered to sum port.
Hi yendori,
Will you explain me hoe the resistor will be dissipating half power.
Its reciprocal network and hence there should not be problem I believe.
Yendori is correct. When used as a power combiner, it depends on whether you are exciting an odd or even mode at both ports.
When exciting an even mode, both branches are perfectly in balance, no current will flow through the resistor and you get the sum of both powers at the input.
When exciting an odd mode nothing gets out!
Exciting at one power combiner input port (typically when combining two signals) is something in between: You can split it into 1/2 odd mode (-6dB) and 1/2 even mode (-6dB). The power of the two even mode inputs will combine, and result in a -3dB loss at the input with respect to the original signal. Which you of course recognize from when using the wilkinson as a splitter. The rest of the power is dissipated in the resistor inside the wilkinson combiner.
It sounds very confusing to me. Can somebody give me a practical example with calculation? Suppose it is an 1:8 way power combiner.
It is interesting to me that power divider works with modes. Please share the paper on modes in power divider and combiner.
In my view its better if we relate with phase than modes.
When an out of phase signals are applied to combiner then the resistor will see he potential difference which will not be the case in equi phase combining.
When the resistor notices any potential difference across it then it is obvious that the power will be dissipated.
Well, let's stick to the original question.
"Can anybody tell me how to choose the Power Rating of Isolation resisters while designing Power Divider?"
Assuming a 0° 2-way power splitter. When operating as a splitter, equal voltage potential appears at end or the resistor, so no power is dissipated.
When operating as a combiner, if you combine 2 signals of equal amplitude and phase, equal voltage potential appears at end or the resistor, so no power is dissipated. So if each signal was 0dBm, they would combine to be 3dBm.
Agian, when operating as a combiner, if you combine 2 signals at 2 different frequencies, half of the power will be dissipated by the isolation resistor. This is due to the 0° phase shift of the resistor and the 180° phase shift of the 2 transmission lines and the power delivered to the load(input). Because of the equal loss through the transmission line and 180° phase difference the signals cancel at the opposite port achieving the isoaltion.
Of course I do not know for what application you power splitter design is for. Is it only used as a power splitter? or will it only combine coherent signals. If it may combine signals of different frequency you need to consider the max power of the signals.
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