Dual-Frequency and Dual-Polarization Passive Millimeter-Wave Imagery

Acquiring diverse information (e.g., polarization, frequency) within a scene can significantly enhance the imaging system's effectiveness and reliability. In this article, we develop a dual-frequency and dual-polarization passive millimeter-wave (PMMW) imager for outdoor imagery. The system is based on a focal plane array (FPA) with a 1.5× 0.8 m parabolic reflector. A row of horizontally polarized W-band radiometers was placed on the focal plane alongside two rows of Ka-band radiometers with horizontal and vertical polarizations. Multiple scanning modes were employed to adapt to various application scenarios. An angle resolution of 0.4° (Ka) and 0.14° (W) is achieved with a 15° field of view, and the thermal sensitivity is about 0.5 K (W) and 0.3 K (Ka). The imager can complete a 360° azimuthal scan in 3 s and achieve full airspace imaging in 18 s. Several outdoor experiments are conducted, which include imaging of stationary targets such as outdoor buildings and trees, as well as moving targets involving commercial aircraft flying in the airspace. The experimental results demonstrate that the proposed imager can accurately capture both stationary and dynamic targets with frequency and polarization diversities.