G. Poesen

Passive Frequency Selective Surface Array as a Diffuser for Destroying Millimeter Wave Coherence

This paper presents the design, construction, and testing of grounded frequency selective surface (FSS) array as a diffuser for destroying millimeter wave coherence which is used to eliminate speckle in active millimeter wave imaging. To create stochastically independent illumination patterns, we proposed a diffuser based on random-phase distributions obtained by changing the incident frequency. The random-phase diffuser was obtained by mixing up the phase relations between the cells of a deterministic function (e.g., beam splitter). The slot length of FSS is the main design parameter used to optimize the phase shifting properties of the array. The critical parameters of the diffuser array design, such as phase relation with slot lengths, losses, and bandwidth, are discussed. We designed the FSS arrays with finite integral technique (FIT), fabricated by etching technique, and characterized the S-parameters with a free-space MVNA, and measured the radiation patterns with a BWO in motorized setup.

W-Band Characterization of Grounded Frequency Selective Surface Arrays Composed of Nonequal Slot Length Subarrays

We present the design and construction of Frequency Selective Surface arrays composed of two subarrays of different slot lengths. We investigated their response variations with the variation of slot length differences of the elementary sub-arrays. Such nonhomogeneous arrays cannot be simulated with Computer Aided Design (CAD) programs because the boundary conditions are not fulfilled by the simulator. In infinite array simulation, the periodic boundary conditions are prescribed on the walls of the unit cell, whereas in the case of sub-arrays of unequal slot length such boundary conditions are not applicable. The CAD simulation of such combined array gives incorrect values of amplitude and phase responses. In this work, we investigate the characteristics of such complex arrays by using heuristic experimental approach. The results of the experimental approach demonstrate that the resultant reflection amplitude and phase of such complex array depend on the difference of slot lengths of the two sub-arrays.