Bandwidth Enhancement of a Dual-Polarized Slot Antenna Using Characteristic Modes

In this letter, a wideband dual-polarized slot antenna is presented. The proposed antenna is designed in a systematic way using the theory of characteristic modes for slot apertures. An H-shaped slot in an infinite ground plane is used as the initial structure for further optimization design. Magnetic characteristic currents for the first four modes of the slot are investigated. To enhance the bandwidth (BW) of the antenna, the geometry of the slot antenna is then modified based on the clear physical insights obtained from the modal analysis. In addition, two pairs of differentially fed capacitive coupling elements are introduced to excite the first two modes of the slot, and an integrated wideband feeding network is designed. An antenna prototype in WLAN 2.4 GHz band is fabricated. Experimental and simulated results show that the proposed dual-polarized slot antenna has a wide BW and good dipole-like radiation characteristics. Compared with the initial H-shaped slot antenna, the BW of the proposed antenna is enhanced from 17% to 46%. The measured port isolation over the entire frequency band is about 26 dB, and the cross-polarization level is over 28 dB for the two polarizations.