A Miniaturized Magic-T Using Microstrip-to-Coplanar Strips Transition and its Application to a Reflection-Type Phase Shifter

This article proposes a miniaturized magic-T and experimentally demonstrates that the magic-T is a suitable hybrid circuit for designing a wideband reflection-type phase shifter (RTPS) with a simple configuration. Conventional RTPSs employ quadrature hybrid couplers with narrow bandwidths and complicated structures. The proposed magic-T makes an RTPS broadband and compact with low insertion loss (IL) and wide relative phase shifts. The practical challenge is that the circuit must achieve compactness, low IL, and wide bandwidth simultaneously. A magic-T that meets the conditions is designed, combining a ring-shaped T-divider with a microstrip-to-coplanar strips (CPSs) transition. The circumference is a half-guided wavelength, and an IL is less than 1.0 dB in a 100% fractional bandwidth (FBW). Then, an RTPS based on the circuit is designed at 2.0 GHz. The prototype has 46% FBW, where |S-{11}| is less than -10 dB, IL of 1.6± 0.5 dB, and relative phase shifts of 290°.