A New Design of Filtering Patch Antennas With Enhanced Bandwidth and Harmonic Suppression

A new design method of filtering circular patch antennas with good harmonic suppression is proposed in this communication. According to the analysis of field distributions of the resonant modes on the circular patch, we initially reveal the mechanism of high-order modes suppression by introducing a pair of common mode (CM) exciting signals with equal amplitude and the same phase at specific locations on the circular patch antenna. Afterward, to implement this design concept, the exciting signals realized by a T-shaped microstrip feed line with two pairs of extra parallel arms are arranged on both sides of the circular patch antenna. Owing to this excitation scheme, the influence of the harmonics of the antenna has been reduced, and two zeros on both sides of the passband are achieved by the cross-coupling form. Besides, an enhanced bandwidth is also realized attributing to an additional resonant mode introduced by the extra parallel arms. Finally, to verify the feasibility of the developed scheme, a prototype filtering antenna is fabricated and tested. Measured results show that the demonstrator exhibits an impedance bandwidth of 10.2% (2.42–2.68 GHz). Inside the passband, the radiation patterns keep basically consistent, and the realized gain (at $\Phi $ = 0° and $\theta $ = 0°) is stable at 7.5 dBi. Compared with the traditional filtering antenna, the harmonic suppression bandwidth in this work ranges to $3.2f_{0}$ ( $f_{0}$ is the center frequency of the antenna) while maintaining a low profile.