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Due to the atmospheric absorption in W-band, especially the spectrum around 94 GHz has been the frequency of choice for radar applications in reconnaissance and metrology, but more recently also for indoor security applications. However, for indoor security applications the propagation environment and scale of the application is quite different as compared to the long-range military and scientific applications. In this paper we report on the work performed at the research group ESAT-TELEMIC on modelling and designing indoor millimeter wave imaging systems that employ coherent multi-parametric illumination in a "flash"-like configuration. We discuss trade-offs between certain system parameters and present two examples of multi-parameter imaging. We show that a 2.5D simulator is a good compromise between computational cost and ability to analyse interference effects such as speckle. We also elaborate on challenges in terms of hardware implementation, and demonstrate experimentally the potential of using printedantennas for millimeter wave security applications.

Coherent imaging systems always suffer from speckle phenomenon, which blurs the image, and therefore making the information extraction quite difficult. Hadamard speckle contrast reduction (SCR) is considered to be effective to deal with this problem in optics. In this paper, we explore the working principle and effectiveness of this approach, from mathematical deduction to system simulation, and from optics to millimetre wave frequencies, so as to understand why it works and how well it can perform. We show that the effectiveness of Hadamard SCR is linked to the texture of the objects' surface. The investigated cases are in the region of both millimetre wave frequencies and optics, but it should be clear that it is a wave-oriented discussion and therefore the problem should be considered in terms of electrical size, beyond the limitation of working frequencies.

Active millimeter wave images typically exhibit characteristic speckle noise, due to the coherence of artificial millimeter wave sources. In this paper we will study the Hadamard speckle contrast reduction (SCR) technique, which has been successfully used in laser projection systems, in the context of millimeter wave imaging. We will show the impact of Hadamard matrix order and pattern size, linked to image and pattern resolution on speckle reduction efficiency. Practical limitations of Hadamard pattern implementations and their effect on speckle reduction efficiency will also be discussed.