A quadrature hybrid comprising first and second coupled open waveguides. Each open waveguide comprises first and second ports. One port in the first open waveguide is used as input port for an input signal which is used to generate I and Q output signals. The other port in the first open waveguide is used to output the Q signal, and one of the ports in the second waveguide is used to output the I signal. The other of the ports in the second open waveguide is an isolated port. The quadrature hybrid comprises a first differential amplifier with positive and negative ports, the positive port being connected to the first open waveguide and the negative port being connected to the second open waveguide.