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Signal flow graph – an additional technique that is very useful for the analysis of microwave networks in terms of transmitted and reflected waves
Consider the flow graph of an arbitrary two-port network
The flow graph gives an intuitive graphical illustration of the network behavior
A wave of amplitude a1 incident at port 1 is split:
1)…part going throughS11 and out port 1 as a reflected wave
2)… part transmitted through S21 to node b2.
3) At node b2:
- the wave goes out port 2;
- if a load with non zero reflection coefficient is connected at port 2, this
wave will be at least partly reflected and re-enter the two-port network at
node a2.
- Part of the wave can be reflected back out port 2 via S22, and part can be
transmitted out port I through S12.
Two other special networks,
1) a one-port network
2) a voltage source, are shown in
The microwave network in signal flow graph form can be used to solve for the
ratio of any combination of wave amplitudes. This can be done using
four basic decomposition rules, but the same results can also be obtained using Mason's rule from control system theory.