An Ultracompact Active Bidirectional Phase Shifter with an Intrinsic Reciprocal Phase Inverting Core

This paper presents an ultracompact active bidirectional phase shifter (ABPS), featuring an intrinsic reciprocal phase-inverting bidirectional variable gain amplifier (PI-BVGA) core. To achieve a compact footprint and high-reliability bidirectional operation, we propose a novel core architecture that intrinsically synchronizes input and output admittances without bulky switching networks. In the proposed PI-BVGA, the transistors in the inactive path are not merely turned off; one is utilized as an input conductance controller via DC bias adjustment, while the other remains fully on to function as an output susceptance equalizer. This technique effectively cancels the parasitic variations, enabling precise matching between forward and backward operations within a significantly reduced area. The proposed ABPS achieves 6-bit phase resolution, exhibiting a root-mean-square (RMS) phase error of less than 2.1$^{\circ}$ and an RMS gain error of less than 0.7 dB in both directions, occupying an ultracompact area of 0.57 mm $\times$ 0.3 mm.