Design Study of Normal Mode Helical Antenna with Dual-Frequency and Circular Polarization Used in Mobile. J. eng. sustain. dev. [Internet]. 2013 Aug. 1 [cited 2024 Jul. 3];17(3):79-93. Available from: https://jeasd.uomustansiriyah.edu.iq/index.php/jeasd/article/view/999