Coupled line coupler with smooth passband based on two-layer structure

Abstract

In the current study, a coupled line coupler with smooth passband based on two-layer structure is proposed. By using second dielectric material slab, the smoothness of coupled line coupler can be refined under the same area of microstrip circuits. The 1dB-fluctuation passband of this coupler is from 12.6GHz to 13.4GHz with maximum S₃₁ of -8.23dB at center frequency of 13GHz whose variance D is 0.069. The applying of second dielectric material slab restructures the coupling length of electrical and magnetic field leading to the refinement of passband. This method is based on the change of wavelength of signal, which means the changing of passband is more obvious in higher operating frequency under a certain variation of wavelength. The second dielectric material slab shall be placed on an accurate position to achieve best smoothness which needed to be well calculated and simulated.