Development of an Equivalent Circuit Topology for a Directional Coupler

GENÇ İ., GÖZEL M. A., kahriman m.

Dicle Üniversitesi Mühendislik Fakültesi Mühendislik Dergisi, cilt.17, sa.2, ss.1-15, 2026 (TRDizin)

Özet

In the design and analysis processes of microstrip directional couplers, full-wave electromagnetic simulations provide high accuracy. Still, they require high computational costs, especially in broadband optimization and system-level designs. This study presents an improved lumped element equivalent circuit topology based on the segmentation principle in transmission line theory, which enables the rapid and accurate modeling of the distributed electromagnetic behavior of physical structures. Within the scope of this study, the performance of different circuit topologies designed in the ADS environment was comparatively analyzed using reference S-parameters obtained with CST Studio Suite. In optimization processes, it has been observed that the physical behavior of fundamental π models is determined by the reflection coefficient (S11), though phase and amplitude errors increase at high frequencies. To overcome this limitation, a final topology was developed by dividing the connecting lines into multiple LC sections and modeling the structural effects. Analysis results show that the Mean Absolute Error value, which was 4.52 dB in the basic models, was reduced to 0.67 dB in the proposed final topology. In particular, the low error rate of 0.64 dB obtained in the transmission characteristic proves that the developed model successfully represents the physical structure over a wide band range. The presented approach combines the accuracy of electromagnetic analysis with the speed of circuit simulation, offering an effective solution for designing complex microwave systems.