Wideband filtering antenna loading U-shaped parasitic patches based on characteristic mode analysis

A wideband filtering antenna loading with U-shaped parasitic patches (UPP) is proposed by the characteristic mode analysis (CMA). The antenna is consisted of two dielectric substrates, one of which is printed with an eight-sawteeth patch, four single-sawteeth patches and two pairs of U-shaped parasitic patches. The sawteeth structures enable the two distinct characteristic modes to be closer with a smaller frequency space while allowing them to coexist within the operating frequency band, significantly enhancing the bandwidth. The two pairs of UPP can generate low-frequency and high-frequency radiation nulls, respectively. Utilizing CMA, potential modal nulls are identified at 4 GHz in the low stopband and at 7.5 GHz in the high stopband. Upon excitation with an L-shaped probe, the antenna exhibits radiation nulls precisely at 4 GHz and 7.41 GHz. The antenna's dimensions are 0.94λ₀ × 0.94λ₀ × 0.066λ₀ (50 mm×50 mm×2.5 mm), where λ₀ represents the wavelength of the center frequency in free space. The measured impedance bandwidth with |S₁₁| below - 10 dB is 26.38% (5 GHz to 6.52 GHz). The gain in the operational bandwidth is fluctuated from 7.21 dBi to 7.98 dBi, while the out-of-band suppression is reached 12.3 dB at a low frequency band and 17.8 dB at a high frequency band. Within the bandwidth range, the cross-polarization level remains under - 31 dB. The proposed antenna characterized by broadband, low cross-polarization, and low-profile, can be widely applied in 5G communication.