A dual-frequency-mode monopole-helical antenna with a parasitic normal-mode helix

A low-profile ann 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 ct coaxial line fed through the ground plane, can be operated nt three resonant frequencies. However, two modes of dual-frequency-band operation at 900 MHz / 1800 MHz and 900 MHz / 1900 MHz are found in the presence of the normal-mode helix mounted directly on the ground plane. A certain height and diameter of the circumference of the normal-mode helix can perform these modes of dual-frequency-band operation, and will be discussed in detail. Also, the approximately Il and 10% of bandwidth performance in lower and upper frequency bands,will be explicitly studied. The dyadic Green's functions are used to obtain the numerical solutions of far field radiation patterns, which are found to be in good agreement with the experimental results. (C) 2001 John Wiley & Sons, Inc