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Background: Star sensor is one of the precise attitude determination sensors. It is an electro-optical system that takes an image from a set of stars and by comparing it with the star catalogue determines angle deviation of the satellite and modifies its attitude. Star sensor is composed of baffle, optical system, detector, and electronic and image processing system.

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In this paper, we report complete design and simulation of a quasi-optical millimeter wave imaging system with Fresnel lens and horn Antenna using ZEMAX and FEKO softwares, respectively. It is much easier to make a Fresnel lens at millimeter wavelengths compared to spherical and aspherical lenses. The use of Fresnel lens to focus millimeter wave radiation greatly reduces the thickness and also the weight of the focusing element from 25 Kg to 4.5 Kg. A horn antenna with Gaussian profile and corrugated walls at the central frequency of 94 GHz for feeding this system is designed. The symmetry of the designed corrugated Gaussian horn radiation pattern in E and H orthogonal planes, its wide bandwidth as well as its low side lobe levels make it a good candidate for feeding a W band millimeter-wave imaging system. The designed quasi-optical imaging system has low weight with high resolution and can be used to detect hidden objects within a distance of 5 meters with 30 mm resolution in W band at 94 GHz central frequency.