Planar rat‐race coupler with microstrip electromagnetic bandgap element

This article presents the design of microstrip electromagnetic bandgap element and its applications in the planar rat‐race hybrid coupler with the purpose of harmonic suppression and size reduction.The measured results of proposed hybrid coupler with 1.25 GHz central frequency verify its attractive performance with an insertion loss of less than 3.4 dB, a return loss of about 20 dB, an isolation of 32 dB, 17 dB suppression for the second harmonic, 25 dB suppression for the third harmonic, and 22 dB suppression for the fourth harmonic. In particular, with no loss of the performance, the area of proposed rat‐race coupler, achieving 57% save in size, has been successfully reduced from 38.82 cm 2 (the area of conventional hybrid coupler) to 16.72 cm 2 .