A detector has been designed and constructed, using a beam-lead diode, directly in a groove guide. A triangular dipole, produced by photolithography on RT/Duroid 5880, is placed transversely across the guide. A GEC beam-lead Schottky diode, bonded across the dipole, acts as the rectifying element. When used with a cylindrical back short-circuit and an appropriate bias current, a voltage sensitivity of about 400 VW⁻¹ and a tangential sensitivity of about −42 dBm was obtained at a frequency of 100 GHz.