Perspectives in microwave circuit analysis

It is shown that computational inefficiency can be avoided by combining the individual subnetworks two at a time, and calculating the S-parameters each time a connection is made, until the complete network is assembled. This technique, called the subnetwork growth method, has the advantage that no large sparse matrices are created. In making a connection there are two distinct operations, depending on whether the ports to be joined are on different networks or on the same network. Formulas for the new S-parameters can be calculated using signal flow graphs. To demonstrate the subnetwork growth method, a microstrip CAD package called Puff has been developed. The circuit description in Puff is stored as dynamic variables that are addressed using pointers. The process of laying out a network consists of building up a linked list of subnetworks and connections. In the analysis stage, Puff collapses these linked lists by making connections until no joints remain. To illustrate a practical design, a simple microstrip low-pass filter, namely a three-stage low-pass Tchebyscheff filter with a 0.1-dB ripple, is built