3-port CRLH (Composite Right/Left Handed) based Differential Phase Shifter (DPS) is proposed. DPS is analyzed by means of an analytical approach and an accurate design method is presented. It is shown the DPS frequency bandwidth may be maximized if a transmission line of optimum length is inserted before the CRLH structure. Based on the proposed design method, a semi-lumped DPS with 90° ±10% difference phase shift over 2.5 octaves is design, developing the circuit layout, too. Using electromagnetic software, it is shown the analysis results for the designed DPS are in good agreement with the expected ones. The 3-port DPS is broadband and small-size, having a convenient topology for applications such as antenna phased array feeding circuits.