An Eigenadmittance Condition Applicable to Symmetrical Four-Port Circulators and Hybrids

Recently, an expression for the equivalent admittance of symmetrical three-port circulators has been derived on the basis of symmetry considerations. In this paper, the same technique is extended to the symmetrical four-port circulator. It is shown that a simple relationship must be satisfied by the eigenadmittances jY₀, jY_-1, jY₁, and jY₂ if perfect circulation is to be obtainable by matching alone. This relationship also applies to recriprocal four-port devices with 2-fold symmetry about two perpendicular axes which are required to be 90° hybrids upon matching, provided that the eigenadmittances jY₁, jY₂, jY₃, and jY₄ are used. An interesting application of this relation to the construction of a compact stripline hybrid is given.