Enhancing the Gain of Helical Antennas by Shaping the Ground Conductor Djordjevic, A. ; Zajic, A. ; Ilic, M. Abstract Publication: IEEE Antennas and Wireless Propagation Letters Pub Date: December 2006 DOI: 10.1109/LAWP.2006.873946 Bibcode: 2006IAWPL...5..138D