A compact 3-db directional coupler using dual transmission lines on dual substrate layer for butler matrix application

In this paper, A compact 3-dB directional coupler using dual transmission lines on dual substrate layer is presented. The proposed coupler comprises of two conductor layer at top and bottom substrates. These two conductors are coupled through a circular aperture in the common ground plane. The simulated proposed coupler is designed using CST Microwave Studio 2010 by using inexpensive FR-4 substrate to operate at 2.45 GHz. The design is able to provide a good size and bandwidth simultaneously, which is not offered by any recent reported structures, i.e., size reduction of 60 % with a simultaneous bandwidth achieved up to 48 %.