Planar High-Isolation Dual-Band Dual-Mode Antenna With Omni-/Unidirectional Radiation

A planar dual-band dual-mode antenna with omni-/unidirectional radiation is proposed for operating 2.45/5.8 GHz bands. The lower-band antenna consists of 4 modified quarter-mode substrate-integrated waveugide (QMSIW) elements, which are excited in-phase and with same magnitude to obtain vertically polarized omni-directional radiation. The upper-band antenna is based on a four-port square patch with differential feed to achieve highly-isolated dual-polarization with broadside radiation. In addition, the square patch is loaded with four overlapped-corner-mushroom structures to broaden the upper bandwidth. The final design with overall size of of 90 90 3.66 mm (0.735 0.735 0.03 at 2.45 GHz) was fabricated and measured. Measurements show a 10-dB return loss bandwidth of 160/400 MHz and a gain of 3.4/8.5 dBi at 2.45/5.8 GHz bands, respectively. Furthermore, the antenna prototype demonstrates an isolation of more than 30 dB among all ports. Especially, the isolation among the two ports of the upper-band elements is better than 40 dB.