This study introduces a low-profile, broadband antenna with filtering features and tunable radiation nulls. The antenna consists of an arc-shaped slot, a sawtooth square slot, a Y-shaped filtering branch, two rectangular metal cavities, and curved current loops. High-frequency current balancing technology is used in this research, two rectangular metal cavities are added above the slot to balance the current strength and reduce cross-polarization. By introducing a Y-shaped filtering branch based on the reverse diversion technique, the filtering capability of the antenna can be significantly enhanced. The electric and magnetic field intensity in the specific area is enhanced through arc-shaped slot tuning technology, and the bandwidth is effectively broadened. The radius adjustment of the sector-shaped feeding network controls the position of the high-frequency radiation null, and the curved current loops control the low-frequency radiation null, the two modulate to regulate the roll-off rate of the radiation characteristic. Experimental tests demonstrate an impedance matching bandwidth greater than 55%, a peak gain of 4.5 dBi, and out-of-band suppression of 25 and 21 dB in the low and high-frequency bands, respectively. Moreover, the cross-polarization level obtained in the xoz plane is lower than –35 dB. The designed antenna demonstrates considerable potential for broadband filtering applications.

In this paper, a high-order-mode (HOM) (TE330) cavity-fed 45° linear polarized 6×6 slot array antenna is proposed. The 45° linear polarization is achieved by introducing asymmetric cross slots on the HOM cavity, resulting in low profile and wide bandwidth. The antenna array was verified using standard printed circuit board technology. Measured results show that the impedance bandwidth ( $|S_{11}|\le$ −10 dB) is 13.9% (36.98–42.92 GHz), and the peak gain is 19.3 dBi with a 3-dB gain bandwidth of 13.6%. Attributed to its simple structure, low profile, and wide bandwidth, the presented antenna is a good candidate for 5G applications.

A two-element low-profile closely coupled dual-band MIMO antenna is demonstrated for WiMAX applications. Based on the principle of metasurface (MTS) decoupling, a double-layer MTS consisting of pairs of elliptic patches with two different sizes is proposed. The MTS is loaded above a coupled dual-band MIMO antenna, and the mutual coupling in the lower and upper band is reduced by the larger and smaller elliptic patches, respectively. The edge-to-edge distance of antenna elements is only 0.01λ0 (λ0 is the free-space wavelength at 2.6 GHz). The measured results show that the working bandwidths of the MIMO antenna are 2.5–2.69 and 3.4–3.69 GHz. The −10 dB impedance bandwidths in two bands are 8.83% (2.49–2.72 GHz) and 8.50% (3.38–3.68 GHz), and the isolation between antenna elements is enhanced by 13.5 and 18.4 dB in two bands, respectively. Moreover, broadside radiation performances in two bands are obtained.

In this paper, a novel compact dual-band microstrip patch antenna with dual-radiation modes is investigated. The proposed antenna consists of a rectangular ground plane, a U-shaped feed probe, and an H-shaped slot radiating patch. By adjusting the size of these structures, a dual-band antenna can be obtained. In the low-frequency band, the antenna can radiate one radiation beam with high gain. In the high-frequency band, the antenna can achieve monopole-like radiation pattern. Therefore, an antenna prototype is fabricated and measured for validation. Good agreement between the simulated and measured results is observed in this paper. The antenna's operating frequency ranges are 3.6–3.85 GHz in the low-frequency band and 5.1–6.1 GHz in the high-frequency band with the reflection coefficient less than −10 dB. At 3.7 GHz, the antenna radiate one beam with 8.8 dBi realized gain. At 5.5 GHz, it exhibits dual-radiation beams directed to −48 and 48° with 5.6 and 5.5 dBi realized gain in the xoz-plane and −48 and 48° with 2.9 and 3.0 dBi realized gain in the yoz-plane. Therefore, the proposed antenna is a good candidate for wireless communication systems.