Unintended illumination for PMMW systems

Abstract

As Passive Millimeter Wave (PMMW) imagers mature, users have located them in more and more challenging locations. Because PMMW systems typically use natural sky coldness as a contrast source, indoor installations can become problematic. A number of semi-active illumination systems have been proposed, with various degrees of success. A problem many of them suffer from is reversed contrast -the illumination source is considerably hotter than the ambient scene, causing the cameras to act in unexpected ways. The relatively narrow extent of the illumination source is another problem, with speckle and glint often dominating the image.There are a number of unintended illumination sources in indoor locations, and all are poorly understood. This paper will examine several of them, as well as their polarametric properties, and discuss their effects on image quality.

Development of passive millimeter wave imaging for concealed weapon detection indoors

“…Multifrequency illumination appears as an attractive adjunct to PMMW imaging indoors, but its practical application requires careful calculations [8].…”

“…Multifrequency illumination appears as an attractive adjunct to PMMW imaging indoors, but its practical application requires careful calculations . A PMMW imaging system with 10 GHz effective bandwidth, and a 70 K sky are assumed.…”

“…In previous researches, the reconfiguration of polarization diversity is discussed for linear polarization (LP) to LP [5], LP to circular polarization (CP) [6], and CP to CP, that is, right-handed CP (RHCP) to left-handed CP (LHCP) and vice versa [7,8]. Especially, for a reconfigurable single-feed microstrip antennas for CP diversity have been implemented by a relatively complex radiator and matching structure because of bias circuits for switching devices and matching networks for changing antenna impedances at each CP sense [9].…”