Broadly this includes devices and products, which generate a form of electromagnetic radiation with RF wavelengths between 300 MHz (wavelength size 100cm) and 300 GHz (wavelength size 0.1cm). This technology is used in PIDS to measure changes in the electromagnetic fields between a Transmitter (Tx) and a Receiver (Rx) caused by intrusion events.  Devices that operate frequencies in the microwave range are often referred to by their IEEE radar band designations such as S, C, X, or K.