A Low-Cost Compact Planar Dual-Band 3 dB Branch Line Coupler Using an Unbalanced CRLH

In this work, a compact dual-band 3 dB branch line coupler (BLC) is designed with center frequency at 2.45 GHz and 5.08 GHz using an unbalanced composite right/left-handed transmission line. Based on the two-port ABCD parameters, the lumped equivalent circuit of the proposed TL is extracted and optimized to obtain characteristic impedance at 2.45 GHz and 5.08 GHz. The right- and left-handed characteristics of the proposed TL are examined. Incorporating the proposed TL, a dual-band BLC with 0.29λ_g × 0.3λ_g size is obtained. The frequency response has magnitude imbalance of 0.8 dB, phase imbalance of 1.8° and 160 MHz bandwidth at 2.45 GHz and magnitude imbalance of 0.81 dB, phase imbalance of 0.006° and 100 MHz bandwidth at 5.08 GHz.