3 dB branch-line coupler with improved bandwidth using PDMS and zoflex conductor

Abstract

Single section branch line coupler is popular because of its simplicity in design and fabrication. But it suffered from narrow bandwidth and poor out of band rejection characteristics. This paper overcomes these limitations by designing and simulating a Broadband 900 hybrid coupler implementable in planar microstrip circuit. Polydimethylsiloxane (PDMS) and a modified Zoflex Conductor (ZC) were used as the substrate and the conductor respectively. Copper particles obtained using Engraving machine was used to improve the conductivity of the ZC. The coupler is meant to operate at 6 GHz. It shows a return loss and isolation better than 18 dB within the frequency range of 3.64 GHZ to 7.64 GHz. The results exhibited a very low insertion loss better than 4 dB, from 3.64 GHZ to 7.64 GHz and a small phase variation better than 900±50 within the passband of 3.86 GHz to 7.34 GHz. A fractional bandwidth of 52.33% was achieved which is more than five times wider than that of conventional single section coupler.