A cavity-backed two-element rectangular loop slot antenna for circular polarization is presented and investigated by using the generalized network formulation based on the equivalence principle. By applying the method of moments, the magnetic current including the effect of the cavity is obtained for a thin rectangular loop slot. Two short-circuiting points are introduced on the slots to get circular polarization and symmetrical radiation pattern. The axial ratio bandwidth (3 dB) with VSWR (2) reaches 7.6%. The measured and computed results are in good agreement.