Compact single-layer microstrip Marchand type balun

In this letter, we propose a novel approach to the design of compact, single-layer microstrip Marchand type balun matched at unbalanced and balanced ports to arbitrarily chosen terminating impedances. An application of coupling enhanced directional couplers for realization of the balun where no additional impedance transformers are required is presented. The proposed concept has been verified by the design of a balun circuit operating at f₀ = 1.5 GHz with impedance transformation 50 Ω_unbal. to 50 Ω_bal. and compared with balun designed using conventional approach. The measurement results proved the performance and validity of the proposed circuit.