Miniature 90° and 180° Directional Couplers for Bluetooth and WLAN Applications Designed as Multilayer Microwave Integrated Circuits

Abstract

This paper presents the designs as well as modeled and measured characteristics of two miniaturized 3-dB directional couplers for wireless applications at 2.45 GHz that provide 90° and 180° phase differences between the output signals. The 90° directional coupler was designed as a branch-line coupler with one pair of quarter-wavelength transmission line sections replaced by artificial transmission lines with positive frequency dispersion and another pair of transmission lines replaced by metamaterial transmission lines with negative dispersion. The 180° directional coupler was designed on the basis of the 90° directional coupler by connecting an additional 90° phase shifting network to one of its outputs. Both directional couplers were implemented as fullyintegrated quasi-lumped-element structures in multilayer LTCC packages, fabricated, and experimentally investigated.