Equivalent circuit models for linear reciprocal lossy distributed microwave two-ports

The modeling of passive microwave structures by equivalent circuit models is an efficient technique which allows to include distributed problems into complex modeling environments at a system level. However, when synthesizing lumped element circuits for electromagnetic structures with large internal propagation delays, the obtained impedance functions exhibit a large number of frequency poles in a given frequency rang. Hence, the equivalent circuit models are represented by a large number of lumped circuit elements. The number of circuit elements can be reduced significantly if also delay lines are included in addition to capacitors, inductors, resistors, and ideal transformers. We discuss a systematic procedure for the generation of combined lumped element and delay line equivalent circuit models on the basis of numerical data is described.