Previous hybrid couplers have output phase difference that have either been 0°, 90°, or 180°. Other phase differences could only be realized using additional phase-shift elements. This increased circuit size and cost, and also degraded overall performance due to interconnecting mismatch losses. The proposed uniplanar arbitrary phase-difference coupler eliminates these additional components, thereby maintaining small size and good performance. Theoretical analysis is presented here together with measured results for two microstrip couplers for verification.