Magnetically coupled quadrature all-pass filter for quadrature signal generation in vector-summing phase shifters

For a vector-summing phase shifter, the quadrature signal generation (QSG) network is crucial. Among the existing QSG networks, a one-stage quadrature all-pass filter (QAF) provides the same bandwidth as a two-stage R-C polyphase filter while exhibiting 6-dB higher voltage gain. Despite all the advantages, the major disadvantage of the conventional QAF is that it contains two inductors, which occupy large chip area. In this work, magnetically coupled QAF (MCQAF) is proposed. In the proposed MCQAF, the two inductors in the QAF are intertwined to reduce the occupied chip area, dispelling the major disadvantage of the conventional QAF. With the magnetic coupling between the inductors considered, the design equation for the inductance in the MCQAF is derived. An MCQAF is designed at 2 GHz in a GaAs integrated passive device process along with a conventional QAF for comparison. The results of this work show that, except for a slightly larger amplitude error, the proposed MCQAF exhibits performances comparable to those of the conventional QAF while the occupied chip area is reduced by approximately 1/3.