Design of A Quadrature Signal Generator with Filtering Response Using Stub-Loaded Resonators

This paper presents a new filtering quadrature signal generator, which can realize the conversion from single-ended signal to four quadrature signals with filtering response. Two different coupled-line topologies, i.e., parallel coupled-line and anti-parallel coupled-line with short-circuited end are discussed to achieve the desired 90° phase difference. Moreover, with resorting to the electric field distribution of a $\lambda$/2 open-circuited transmission line, the inherent out-of-phase characteristic can be obtained. Based on the above discussion, a four-way quadrature signal generator with filtering response can then be realized using coupled stub-loaded resonators. Measured results show that the designed four-way filtering quadrature signal generator operates at 2.0 GHz with 0.5 dB magnitude imbalance and $90 \pm 5^{\circ}$ phase difference.