a microstrip hybrid ring coupler providing the same function as a convental magic tee in waveguide or a coaxial rat - race . the ring is comprised of four equal electrical length arcs between the input - output ports . the 180 ° phase shift is introduced in one of the four ring arcs by a tightly coupled parallel strip conductor which extends towards the interior of the ring and has an electrical length of λ / 4 where λ is the wavelength at the midband operating frequency of the coupler .