A Novel Configuration of Microstrip Coupler with Low Loss and Suppressed Harmonics

This work presents a novel structure to design a microstrip coupler. The best values of S21 and S31 are 0.65 dB and 0.83 dB, respectively, in the passband of the proposed coupler. Another significant advantage of this coupler is its filtering frequency response, where it can suppress the harmonics below the passband from DC and above the passband, from 1st up to 7th harmonics. The phase difference between S21 and S31 is 90°±0.1°, which indicates a high phase balance. Beside these features, a compact size of 0.01 λg2 is achieved using the proposed novel configuration of the microstrip coupler. A perfect mathematical design method is introduced to show how the insertion loss (IL) can be reduced. Two BPFs are designed, analyzed and placed in the coupler structure. Finally, the designed coupler is fabricated and measured to verify the simulation results, where the experimental results are close to the simulated results.