A Small Planar Log-Periodic Koch-Dipole Antenna (LPKDA) Dimitrios E. Anagnostou* (1) , John Papapolymerou (1) , Christos G. Christodoulou (2) and Manos Tentzeris (1) (1) Georgia Institute of Technology, ECE Department, Atlanta, GA, 30308, USA (2) University of New Mexico, ECE Department, Albuquerque, NM, 87106, USA Abstract—Koch dipole elements are introduced in a planar log-periodic dipole antenna array, in order to minimize its size. The advantages and disadvantages of the proposed LPKDA array are presented and discussed with an emphasis on the minimization characteristics of the design. Index Terms –Antennas, Array, Fractal, Koch, Log-periodic I. INTRODUCTION Log-periodic dipole antenna (LPDAs) arrays used in radio signal detection applications have been constructed so far using Euclidean radiating elements and have achieved high directivity and low cross-polarization ratio over a very wide frequency range. In applications where space constraints restrict the use of full-sized elements, alternative smaller designs need to be considered. In this work, Koch fractal dipoles are introduced as the basic structural elements of a planar Log-Periodic Koch-Dipole Antenna (LPKDA) array, thus replacing the full-sized Euclidean monopoles. Design considerations are presented herein and the performance characteristics of the proposed antenna are discussed. II. LPKDA ANTENNA DESIGN The primary goal in this work is the proof of concept of a log-periodic Koch-dipole antenna (LPKDA) array design. This antenna will be used to cover the 2 – 3 GHz frequency range. For a Euclidean log-periodic dipole antenna (LPDA) array, the largest element’s dimensions can be determined by the lowest desired frequency of operation. The antenna is fabricated on t = 1.588mm thick FR-4 substrate with relative permittivity of ε r = 5. Initially, matched single-element designs for Euclidean and Koch- shaped monopoles at the low frequency end were studied and their characteristics are summarized in Table I. It can be seen that a 28.4 mm long Euclidean element resonates at 1.82 GHz while the vertical length of a Koch element can be only 25.6 mm. The percent vertical-size reduction with respect to the Euclidean element is: . . . . . . Eucl Vert Koch Vert Eucl Vert Length Length Length − = 9.9%. Also, the percent reduction in the vertical length of the Koch element with respect to its own total length is given by: U.S. Government work not protected by U.S. copyright 3685