Design and fabrication of simple and frequency-adjustable dual-band and triple-band antennas

A novel dual-band antenna and a triple-band monopole antenna were developed and fabricated on an Al₂O₃ ceramic substrate with a thickness of 0.4 mm. An L-shaped electrode structure with two branches of different lengths was designed for the antenna with two resonant frequencies, and a W-shaped structure with triple branches of different lengths was designed for the antenna with three resonant frequencies. The two antennas had simple structures, and the resonant frequency could be easily adjusted by changing the length of each branch. A stub was added to both antennas at the input microstrip line to control the input impendence, which gave the antennas better radiation (S₁₁) properties. For the L-shaped antenna, the designed dual resonant frequencies were 2.4 and 3.5 GHz and for the W-shaped antenna, the designed triple resonant frequencies were 2.4, 3.5, and 5.7 GHz. The lengths of the radiation lines, the length of the ground plane, and the length between the tuning stub and the two radiation lines were used as design parameters. Different design parameters were changed to determine how this would affect the antennas’ characteristics. We found that the different parameters had large effects on the return loss (S₁₁) value, and that stub length had a large effect on the resonant frequencies and return loss values.