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Design of a compact ultra wideband 3 dB microstrip-slot coupler with high return losses and isolation

The paper presents the configuration and design method of a compact ultra wideband 3 dB directional coupler with high return loss and isolation. The proposed device is formed by two elliptically shaped microstrip lines, which are broadside coupled through an elliptically shaped slot. In order to improve this coupler's return loss and isolation characteristics a small conducting disk of elliptical shape is included between the two microstrip lines. Results of the full electromagnetic simulations show that the coupler exhibits a coupling of 3.4 dB ± 1.2 dB accompanied by the isolation and return loss of more than 28 dB across the frequency band of 3.0 to 12.0 GHz.