Abstract
High-performance dual-band Doherty power amplifler and non-uniform circularly polarized antenna array require impedance- transforming unequal dual-band 90 - branch-line couplers for power dividing and phase shifting in the feed networks. In this paper, an analytical design methodology of generalized impedance-transforming dual-band branch-line couplers for arbitrary coupling levels is proposed. The coupler features wide range of realizable frequency ratio, multiple ∞exible selections of open- or short-circuited and pi- or T-network topologies. For demonstration, four numerical examples with difierent parameters are presented. Furthermore, two microstrip couplers based on open-circuited pi- and T-network topologies were fabricated and measured. The measured results show good performance at dual 1.8/3.45GHz bands. The fractional bandwidths deflned by the ∞uctuation of the coupling level and the phase difierence less than §0:5dB and §5 - are up to 17% and 18%, 18% and 2% for open-circuited pi- and T-network topologies, respectively.
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