Multiplicative Frequency Diverse Active Incoherent Millimeter-Wave Imaging

In this letter, we present a new approach to mitigating interference and other wavelength-dependent spurious signals in active incoherent millimeter-wave (AIM) imaging using frequency diverse image formation. AIM imaging uses active transmission of noise signals to support Fourier-domain imaging with less bandwidth and integration time than passive imagers, leading to high-speed millimeter-wave imaging capability. However, narrowband operation can be impacted by interfering transmitters and wavelength-dependent spurious responses. By hopping a narrow instantaneous bandwidth between a small set of separate carrier frequencies, such spurious signals can be mitigated via mutual processing of the images formed at each frequency. The concept is demonstrated using an AIM system forming images in 1 GHz frequency steps at carrier frequencies between 37 and 39 GHz operating, with a baseband signal bandwidth of 50 MHz. Images are formed at each of the three carrier frequencies, and are subsequently multiplied to form a joint reconstructed image. Interference cancellation is demonstrated by transmitting a signal at 37 GHz from the back of the scene, a signal that may cause a false target at a single carrier but is mitigated using the frequency-diverse approach.