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# real and reactive power

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#### elektr0

##### Full Member level 5
reactive power in waveguides

Hallo,

scattering parameter description is the most common way to analyze microwave circuits. The forward and backward travelling power waves a,b are either defined as quantities, proportional to the real power of the travelling voltage,current v,i waves or as the real power of the travelling electromagnetic field waves E,H.
Phases from a,b are defined as the phase of v,i or E,H at an arbitrary starting point (time and place).

My question is, how to extract the REACTIVE POWER part on any port of a circuit.

elektr0

L and C.

#### elektr0

##### Full Member level 5
TEM waves do only carry real power, but TEM wave propagation is based on L and C in transmission line theory.
The waveguides capacitance and inductance has nothing to do with the reactive power.

#### eastern

##### Member level 1
Well let's see what do we mean by the term "port"
A "port" is defined to consider the power exchange between different elements of a circuit. But by "reactive power" we mean "storage" of energy in space. So a port can not represent the stored energy as it is clearly a factious surface (not volume).

#### Wiley

##### Member level 4
I am assuming you have some MIMO circuit. Whether it's a section of coupled lines or a patch antenna, it does not matter.

Start with the basic definition of power:$P + jQ = (1/2) V I^*$, where Q is the stored energy. Assuming you know the network parameters, then replace I with Y*V.

If you actually have a waveguide, i.e., a non-(quasi-)TEM mode, things are more complicated. However, if you have defined your voltage and current waves so that $P^+ = (1/2) V^+ (I^+)^*$ and $P^- = (1/2) V^- (I^-)^*$, you should still be able to use the basic circuit definition of power.

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