Systematic Design of UWB Monopole Antennas With Stable Omnidirectional Radiation Pattern

This letter proposes a simple design approach to gain stable omnidirectional radiation pattern in printed ultrawideband (UWB) antennas. Monitoring of the current distributions in different frequencies shows that a combination of standing and traveling modes exists on the antenna. By determining the dominant mode at higher and lower frequencies, the corresponding optimum size of antenna that guarantees a stable omnidirectional radiation pattern and a good return loss is obtained. Using the proposed method, two compact antennas with circular ground and miniaturized fractal ground are designed. Simulation and measurement results show a good impedance matching and an excellent omnidirectional radiation pattern for proposed antennas.