Miniaturized design of rat-race coupler by utilizing T-shape stubs

Nowadays, demands for fully integrated and miniaturized Radio Frequency Integrated Circuits have increased in wireless microwave communication system. Passive components such as coupler, divider and filters are always fabricated in outside of Integrated Circuits, which have been a great barrier to a realization of a fully integrated design. To solve this problem, miniaturization of passive components is one of the big issues at the present time. This paper shows the development of important microwave passive component, rat-race hybrid coupler 180 degrees for LTE higher (1.7-2.7 GHz) frequency band, which is obtained by replacing (3 lambda/4)-wave transmission line of a conventional coupler by their equivalent T-shape line section, resulting in significant size reduction. The miniaturized Rat-Race Hybrid Coupler 180 degrees (RRHC) is designed on a low cost material using a substrate material of FR-4 with dielectric constant (4.3), substrate thickness (h = 1.570mm). The design and simulated results are validated by Method of Momentum using the Advance Design System (ADS) tool from Agilent technologies. The size of the implemented rat-race coupler is 76.11x37.24 mm(2), which is 28% compared to the conventional couplers for higher frequency band. Also, the reflection coefficient, the isolation and the phase difference between two output ports are as good as conventional one and coupling procedure is similar or better than it. (C) 2018 The Authors. Published by Elsevier B.V.