Design of Nonplanar Monopole Antennas With Enhanced Frequency Reduction for Short-Range Wireless Applications

In this study, we explored three-dimensional configurations comprising a monopole-coupled copper wire S-hook, a cross metallic plate, an intersection cross metallic plate, and a spiral wire spring, with the aim of enhancing lower frequency resonance compared to quarter-wave resonance. The original resonance frequency of the quarter-wave monopole, initially at 2.05 GHz, was significantly reduced by 46.88% through effective coupling with a copper wire S-hook. Coupling the quarter-wave monopole with a cross metallic plate resulted in a noteworthy decrease of 54.59% in resonance frequency, while coupling it with an intersection cross metallic plate led to a substantial decrease of 64.24%. The primary objective of connecting a wired S-hook to metallic plates was to achieve a significantly lower resonance frequency. Additionally, efforts were made to reduce resonance frequency by employing a spiral wire spring, which exhibited a remarkable 84.63% reduction. The -10-dB bandwidth varied among the configurations, with values of 14.63% for the quarter-wave monopole, 24.93% for the monopole coupled with a wire S-hook, 27.96% for the monopole coupled with a cross metallic plate, 33.78% for the monopole coupled with an intersection cross metallic plate, and 4.69% for the monopole coupled with a spiral wire spring. The "Ka" values for the monopole coupled with the copper wire S-hook, cross metallic plate, intersection cross metallic plate, and spiral wire spring were 0.41, 0.35, 0.27, and 0.11, respectively, classifying these antennas as electrically small antennas. The achieved resonant frequencies hold potential applications in various wireless communication scenarios, with experimental results from fabricated prototypes showing good agreement with simulation results.