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Abstract
A planar 3 dB patch hybrid coupler using cross and circular-shape slots is presented for a dual-band application. By inductively loading a pair of cross slots and four circular holes on a square patch, the matching and isolation performance of the miniaturized patch hybrid coupler is improved. In addition, the open-circuited shunt stubs are further installed at four ports to realize two operating bands. Since the slotted patch resonator cannot be characterized by the closed-form transmission line theory, the particle swarm optimization (PSO) algorithm is constructed and integrated with a full-wave solver to determine the variable parameters of the proposed structure. Finally, a prototype dual-band coupler operating at 915 MHz and 1575 MHz is designed and fabricated. Measured results show a good agreement with those obtained from simulation.