Scheiner, BenedictBenedictScheinerMichler, FabianFabianMichlerLurz, FabianFabianLurzWeigel, RobertRobertWeigelKölpin, AlexanderAlexanderKölpin2020-04-012020-04-012020IEEE Microwave Magazine 1 (21): 8913696 (2020)http://hdl.handle.net/11420/5586In 1904, the first remote ranging system based on electromagnetic waves was put into operation to monitor approaching ships on the Rhine River [1]. Shortly afterward, the systems were improved to track airplanes in the sky, and they obtained the acronym radar during World War II. Although these targets were large objects and moved with relatively high speeds, engineers almost immediately started to work on solutions for improving the resolution and sensitivity of these systems. Rapid progress in the fields of RF engineering and circuit design finally led to highly compact and energy-efficient radar systems that could take measurements in the micrometer range [2], [3]. This created novel fields of application as the new systems complemented or replaced conventional wired sensors, which might be inoperable in harsh environments or cause discomfort due to the required contact. One example is the touchless measurement of vital signs, whereby radar systems monitor heart and respiration rates as well as blood pressure by evaluating the distance between the system and patient [4], [5]. Also, in many industrial applications, radar systems can outperform conventional sensors, such as when extremely high precision is required in harsh environments [6], [7].1527-3342202018895Journal Article10.1109/MMM.2019.2945150Other