An Analytical Insight on the Frequency Behavior of Rat-Race Coupler

Inhalt:
The 180deg Ring Coupler, also known as the “ratrace” hybrid coupler, has been known in microwave engineering for many decades. It is used in numerous applications as for example mixers, phase shifters, filters or baluns. In the classical literature the rat-race coupler is usually analyzed using evenand odd-mode decomposition. In this paper we present an additional theoretical treatment by directly applying network analysis without further symmetry considerations. This results in a very simple and descriptive formula providing an insight on the coupler’s theoretical full range frequency characteristics using Y-parameters. The analytical expressions are confirmed by simulations and measurement. The insight presented in this paper could be useful for understanding the broadband behaviour of the coupler.