1. Bukhari, N.: Nokia Mobile Phones Ltd. Salo Finland‘Antenna’, GB, (2271670)14.10.1992 (20.4.1994)
2. Siwiak, K., Garay, O.M., and Balzano, Q.: Motorola Inc. Schaumburg IL USA‘Helical antenna structure capable of resonating at two different frequencies’, US, (4443438)29.3.1982 (10.4.1984)
3. Fundamental limitations in antennas
4. Fujimoto, K., Henderson, A., Hirasawa, K., and James, J. R.: ‘Small antennas’, (John Wiley & Sons Inc. New York 1987), p. 295
5. Theoretical limitations on the broadband matching of arbitrary impedances