Flexible branch-line coupler using rubber conductive Zoflex for conformal application

Abstract

This letter presents the design of a flexible branch-line coupler (BLC) using a rubber conductor (Zoflex) as the conductive element and polydimethylsiloxane (PDMS) as a substrate. The BLC is meant to operate at 6 GHz operating frequency. The use of PDMS material as a substrate for the BLC design adds a special characteristic of the PDMS on this passive microwave device. The PDMS has some unique properties such as transparency, durability, and lightweight. Moreover, its high electrical resistivity of 2.9 × 1014 Ω m and moderate dielectric constant of 2.7 make the PDMS a good substrate material for flexible devices. This desirable property gives the proposed device full range of flexibility and a great advantage in terms of durability without degrading the performance of the BLC. From the results obtained for bending and non-bending conditions, it can be seen that within the frequency range of operation, both the return loss and the isolation are kept below the theoretical value of −10 dB. The slight difference observed in the simulated and measured FBWs is due the fabrication tolerances.