Miniaturized Rat-Race Coupler With Harmonic Suppression

In this letter, a miniaturized rat-race coupler with harmonic suppression is proposed. The quarter-wavelength transmission lines in a traditional rat-race coupler are substituted by their equivalent stub-loaded transmission lines. As a result, the overall size is significantly reduced while maintaining the coupler performance. Furthermore, one transmission zero is introduced by the stubs to suppress the harmonics. Finally, a miniaturized rat-race coupler with harmonic suppression is designed, fabricated and measured, and the measurement verifies the theoretical and simulation analysis.