  Non-contact vital sign detection is a required application nowadays in many
fields as patient monitoring and static human detection. Within the last
decade, radar has been introduced as a smart and convenient sensor for
non-contact respiration monitoring. Radar sensors are considered suitable for
such application for its capability to work through obstacles and in harsh
environmental conditions. FMCW radar has been introduced as a powerful tool in
this field for its capability of detecting both the breathing target position
and his chest micro-motions induced due to breathing. Most of the presented
techniques for using the radar for respiration detection is based on bandpass
filtering or wavelet transforms on the required harmonics in either the range
or Doppler dimension. However, both techniques affect the real-time capability
of the monitoring and work on limited distances and aspect angles. A
recognizable fluctuation effect is observed in the received range spectrum
overtime due to respiration chest movements. The proposed technique in this
paper is based on detecting and processing the power changes in real-time over
different aspect angles and distances. Two radar modules working on different
carrier frequency bands, bandwidths and output power levels were tested and
compared.
