Dual-band rat-race coupler design in multilayer LTCC

This paper proposed a new topology of artificial transmission line for the design of dual-band rat-race couplers. Π-shaped circuits consisting of lumped elements are employed to substitute the quarter wavelength transmission lines used in a traditional rat-race coupler, thus result in a compact circuit size. Due to the resonance structures, the proposed Π-shaped circuits can achieve 90 and 270 degree phase responses at two arbitrary design frequencies, respectively. To verify the design concept, the proposed coupler is designed in low-temperature co-fired ceramic (LTCC) technology with operating frequencies at 1 and 2 GHz. The simulation results show good agreement with the design specification. The circuit area occupies only 0.025 × 0.02 λ_g².