A variable line extender for wave guide comprising an elongated electrically conductive housing member and an electrically conductive slide member, the slide member having a convex shaped rounded end and a U-shaped recess extending transversely continuously from one end of the slide longitudinally along one side thereof, around the rounded end, and then along the other side back to the first end, with said housing having a pair of wave guide shaped ports in register with the U-shaped recess of the slide member. Means are provided for adjusting the relative longitudinal position of the slide with respect to the housing so as to vary the length of the path between the ports.