A broadband and compact asymmetrical backward coupled-line coupler with high coupling level
A new wideband asymmetric microstrip coupled-line coupler with 3dB coupling value and quadrature phase difference is presented. Compared with the conventional edge-coupled couplers, this structure, consisting of two different transmission lines (interdigital and conventional microstrip transmission lines) as coupled lines, achieves wider operating bandwidth and larger coupling level. The coupled-line length of the proposed structure is approximately ?g/4. To characterize the structure, an equivalent circuit model has been established. A 3dB designed and fabricated coupler with 0.2mm spacing between coupled lines exhibits an amplitude balance of 2dB from 2.2GHz to 4.2GHz. Good agreements between the full-wave simulation and equivalent circuit model results has been achieved and verified the effectiveness of the proposed circuit model. Also, measurement results have been presented.
microstrip coupled-line coupler asymmetrical coupler backward broadband coupler interdigital capacitor