Two-Section Branch-Line Coupler with Optimal Performance for Dual-Band Applications

This paper presents the design of a two-section 90 degrees hybrid coupler in microstrip technology for dual-band applications. In contrast to the standard design found in the literature, whereby the performance is optimized at a central frequency, the proposed approach aims at performance optimization in two different bands. The application aimed in this work is to feed navigation antennas, which should operate in two bands centered at 1.176 GHz (L5 band) and 1.575 GHz (L1 band). The design is done using the electromagnetic simulator ANSYS HFSS. Validation of the proposed design has been achieved by fabrication of a prototype and good agreement between simulated and measured results has been achieved. The measured output power unbalances are 0.67 dB in the L1 band and 0.18 dB in the L5 band. The reflection coefficient was below -20 dB in both bands, hence indicating that the design strategy was successful.