A miniaturized lumped-element quadrature hybrid with a high density stacked structure is proposed in a 24-layer low temperature co-fired ceramic (LTCC) substrate. Stacking vertical-interdigital-capacitors (VICs) and vertically-spiral-inductors are for an entire size reduction. The transition between inductors realized in the inner space of the inductor further improves the utilization of three-dimensional space. The overall size of the quadrature hybrid is only 10.1×3.8×2.4 mm, or equivalently 0.0040×0.0015×0.0009λg3, which achieves a size reduction of 30.2%. Meanwhile, the proposed hybrid operates at 60 MHz with a fractional bandwidth (FBW) of 33.3%. The measured S11, S21, S31 and S41 are -14.5, -3.8, -3.7, and -14.2 dB within the operating frequency band, respectively, and both of the low phase imbalance and amplitude imbalance are achieved.
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