Dual frequency monopole-helical antenna by using a parasitic normal mode helix for mobile handsets

A low profile and compact monopole-helical antenna with a parasitic helix mounted in parallel with the ground plane is designed. The monopole-helical antenna, which is placed along the axis of a coaxial line fed through the ground plane, can be operated at three resonant frequencies. The helix, which is designed to operate at the normal mode, is mounted directly on the ground plane. Combining both elements together, two modes of dual frequency band operation 900 MHz/1800 MHz and 900 MHz/1900 MHz are found by altering a height of the normal mode helix as well as a diameter of its circumference. The Method of Moments (MoM) and dyadic Green´s functions are used to obtain the numerical solution of far-field radiation patterns, which are found in good agreement compared to the experimental results. The bandwidth performance in dual-frequency operation would also be explicitly studied