Broadband Millimeter-wave FMCW Radar for Imaging of Humans

We present design and realization of a broadband FMCW Radar working in the Millimeter-Wave (MMW) region. The usable frequency range lies between 91GHz and 102GHz. We use a homodyne radar setup. Thus only one MMW source is necessary which is used for TX and LO generation simultaneously. The complex RX radar signal is calculated by a Hilbert transform in order to avoid a broadband MMW IQ mixer. A free space calibration procedure is used to obtain a flat amplitude response and a fixed phase center. Static non-linearities of the transmitted chirp signal are compensated by predistortion of the VCO’s tuning voltage characteristic. A microwave coaxial delay line combined with a time domain resampling method corrects dynamic non-linearities. The ultra wide bandwidth of 11GHz is necessary for the purpose of a high resolution imaging task. Due to the fact that MMWs propagate easily through common clothing it is feasible to image objects like concealed weapons worn beneath the cloth. Imaging of humans in the MMW region is one possibility to enhance the capabilities of nowadays security checkpoints, e. g. at airports.