ABSTRACT We propose a novel omnidirectional broadband filtering antenna that utilizes three half‐wavelength dipole patches of different shapes. Guided by the cross‐coupling theory, the antenna introduces two radiation nulls at low and high frequencies by changing the coupling methods between the dipole patches. Additionally, a C‐shaped resonant ring is incorporated to introduce a third radiation null to enhance the antenna's filtering performance. Impedance matching is achieved by adding slots to the dipole antenna. The operating range of this filtering antenna is from 1.62 to 2.65 GHz, with a relative bandwidth of 48.36% and a center frequency of 2.13 GHz. The in‐band gain ranges from 1.74 to 2.22 dBi, with stable gain within the passband. The out‐of‐band radiation suppression is 11.5 dB at the low‐frequency end and 12 dB at the high‐frequency end, indicating good filtering characteristics. The three nulls are located at 1.48, 2.75, and 3.15 GHz, respectively. The antenna's efficiency within the passband is above 90%, while the out‐of‐band efficiency remains below 10%.
Dong et al. (Sun,) studied this question.