Compact LTCC Rat-Race Couplers Using Multilayered Phase-Delay and Phase-Advance T-Equivalent Sections

In this paper, compact low-temperature co-fired ceramic (LTCC) rat-race couplers are developed using multilayered phase-delay and phase-advance T-equivalent sections. By taking advantage of the multilayered LTCC layout capability, compact 3-D phase-delay and phase-advance T-equivalent sections are designed, and then treated as fundamental elements to construct two types of LTCC rat-race couplers. One type of coupler consists of three phase-delay and a phase-advance sections, whereas the other type coupler is integrated by a phase-delay and three phase-advance sections. At the design frequency 2 GHz, both two types of couplers occupy 3.8 × 3.8 mm2 circuit sizes, namely areas of 0.025 ¿0 × 0.025 ¿0 , where ¿0 is the free-space wavelength. The measured results of the developed couplers agree the simulated results very well. It demonstrates that using multilayered phase-delay and phase-advance T-equivalent sections is an effective approach to miniaturize the circuit size of the rat-race coupler.