Wideband Imaging Array Using Orthogonally Fed Dual Varactor-Loaded Elliptical Slots

Recent advances in several technological fronts have made it possible to design and develop real-time microwave imaging systems (cameras) for use in a wide range of applications. Proper design of the individual antenna array element in these systems is of critical importance. Furthermore, wideband versions of these imaging systems, which are capable of one-sided operation and in conjunction with advanced synthetic aperture radar imaging algorithms, can produce high-resolution 3-D holographical images. In this paper, an orthogonally fed, small elliptical dual varactor-loaded slot antenna, operating in K-band (18-26.5 GHz), is designed for use in such imaging systems. The feed design uses a coplanar waveguide with a 90° bend without a direct dc connection to the antenna. This feed structure accommodates effective placement of required switches while enabling one-sided measurement. Finally, the slot is loaded with two varactor diodes resulting in 3.5 GHz of bandwidth suitable for high-resolution microwave 3-D holographical imaging. The design of this slot and a (1/4) array of such slots is presented. Two arrays are fabricated and used independently, as well as simultaneously, to form (mono- and bistatic, respectively) imaging results.