Design of a Compact Tapered Slot Vivaldi Antenna Array for See Through Concrete Wall UWB Applications Yazhou Wang, Aly E. Fathy EECS Department, University of Tennessee, Knoxville, USA ywang34@utk.edu Abstract An optimized 1 ×8 Vivaldi antenna array designed for the lower-band UWB (2-4 GHz) through-wall imaging systems has been developed. Tapered slot antennas were utilized as the array elements and optimized to have a compact size. A one to eight wideband Wilkinson power divider was designed and fabricated to compose the feed network for Vivaldi antenna array. Measured results of the manufactured Vivaldi antenna array are in excellent agreement with the simulated ones, with a gain of more than 12 dBi within the operating band. The developed array is an essential component for see through concrete wall applications, and very similar in size and gain to the previously developed Vivaldi antenna (around 10 GHz) by our group for drywall-high resolution detection. 1. Introduction Vivaldi antennas have received considerable attention due to their high gain, relatively wide band, simple structure, easy fabrication, and wide use in UWB applications. Their small lateral dimensions and simple integration make them excellent candidates for array development [1]. Federal Communication Commission (FCC) approved a 1.99 GHz to 10.6 GHz frequency band for use in UWB through-wall imaging systems [2]. Yang et al. [3] designed a Vivaldi antenna array around 10 GHz for UWB see-through-wall radar utilizing antipodal Vivaldi antennas with Wilkinson power divider for binary feed. However, the size of this 16-element array is relatively too large if the antenna array is duplicated for the lower-band UWB applications; i.e. close to 3 GHz. Therefore, we used here only an 8-element array and optimized its performance to sustain similar almost constant gain over its operating band. Similar concepts to that utilized by Abbosh et al. [4] to design a compact UWB antipodal Vivaldi antenna have been utilized here. In this paper, we have developed a Vivaldi antenna array for see through concrete wall UWB applications utilizing tapered slot antennas (TSA) and Wilkinson power divider. The configuration of the array element was optimized to have a compact size. Compared with the array in [3], the newly designed array operates at a lower band (2-4 GHz) with a similar size and has more than 12 dBi gain at the operating band. Details of the developed Vivaldi antenna, Wilkinson power divider, the 1×8 Vivaldi antenna array, its simulation and experimental results are presented in this paper. 2. Tapered Slot Antenna Configurations The design parameters of the proposed TSA and the fabricated parts are shown in Figs. 1 and 2 respectively. The manufactured TSA was fabricated on Rogers RT5880 material with a relative dielectric constant of 2.2, thickness of 1.575mm (0.062”) and a loss tangent of 0.0009. The top layer shows the microstrip line and the series radial stub used for feeding the tapered slot antenna. The bottom layer indicates the exponential taper profile [5] which is defined by the opening rate and the two points R ( ) 1 1 1 , y x P and ( ) 2 2 2 , y x P (1) 2 1 c e c y Rx + = where 1 2 1 2 1 2 2 1 2 1 2 1 Rx Rx Rx Rx Rx Rx e e e y e y c e e y y c − − = − − = (2) Given the highest frequency of operation , the width W of the tapered slot antenna should satisfy equation (3) to circumvent the grating lobes of Vivaldi array. ( H f )