Multiplicative Frequency Diverse Image Formation in Active Incoherent Millimeter-Wave Imaging

Abstract

Active incoherent millimeter-wave imaging systems reduce the bandwidth requirements of passive systems by increasing the signal-to-noise ratio using incoherent signal illumination and therefore mitigating high sensitivity requirements on the receiver. As a result, active incoherent millimeter-wave imaging systems can operate with much narrower instantaneous bandwidths than passive imaging systems. However, narrow bandwidths can pose problems in terms of target interference that can impact image formation. In this work, we present a frequency diverse active incoherent millimeter-wave imaging array that uses a frequency hopping scheme to control the electromagnetic radiation. By changing the frequency, wavelength-dependent interference issues are reduced. We employ a multiplicative processing approach that reconstructs images at each frequency and multiplies the reconstructed images. The concept is demonstrated using an active incoherent millimeter-wave imager operating with a signal bandwidth of 50 MHz at 1-GHz frequency steps between 36-40 GHz. We demonstrate reconstruction of a reflecting object with multiple scattering points, showing that the multiplicative frequency diverse approach obtains better images than individual frequency images.