A distance measuring device and method for determining distance, and a suitable reflective member are provided. The distance measuring device includes analysis electronics and a sensor device, which has at least one coupling probe for feeding a transmission signal into a line structure. A reflective member is disposed in the line structure which has a base plate with an attached collar forming a cup-shaped element, and a feed block with a recess into which the collar plunges. The recess has a sealing ring which produces airtightness with the collar, wherein the attached collar is provided on the front face with a plastic plate.