Theory
The scattering parameters for the common case of a 2-way equal-split Wilkinson power divider at the design frequency is given by
Inspection of the S matrix reveals that the network is reciprocal, that the terminals are matched, that the output terminals are isolated (=0), and that equal power division is achieved . The non-unitary matrix results from the fact that the network is lossy. An ideal Wilkinson divider would yield .
Network theorem governs that a divider cannot satisfy all three conditions (being matched, reciprocal and loss-less) at the same time. Wilkinson divider satisfies the first two (matched and reciprocal), and cannot satisfy the last one( being loss-less). Hence, there is some loss occurring in the network.
No loss occurs when the signals at ports 2 and 3 are in phase and have equal magnitude.
The picture below shows a typical output expected from a Wilkinson Power Divider. The are almost -3 dB, and the is low near the design frequency.
The picture below demonstrates a very high isolation between output ports (port 2 & 3)
However, some modification can be done to achieve unequal power division at the output ports. By cascading, the input power might be divided to any -number of outputs.
Read more about this topic: Wilkinson Power Divider
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