The most widely used topology in the design of the cellular stripline circulator is that comprising a planar gyromagnetic resonator, biased above the uniform mode resonance, symmetrically coupled by quarter-wave transformers between ferrite substrates. Its operation is still, however, largely semi-empirical. The purpose is to reconcile, in the case of a side-coupled triangular resonator, its network, magnetic and physical parameters. The magnetic variables of the substrate are uniquely established by the weakly magnetised model of the gyrator circuit and its effective permeability. The procedure outlined here is applicable to the construction of devices below 2GHz with specifications of up to 25 bandwidth at 1.20 voltage standing wave ratio (VSWR) points (23dB isolation). This sort of circuit is met in the design of ultra high frequency (UHF) circulators for use in cellular products. © 2009 The Institution of Engineering and Technology.