A planar beamformer for use with a array antenna includes a dielectric sheet defining first and second broad sides. 01 to about 1000 Torr at below 1000\xb0 C. The portions of the outer joint member that are finished by cold forging are track grooves, radially inner spherical-surface portions, a cup-inlet chamfer, track chamfers, track-inlet chamfers, a part except for a boot fixing portion on a radially outer surface of the cup section, and a center hole at an end surface of the shaft section. This ratio can be displayed and used to control the speed of the towing vehicle.