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 2.45/5.8 GHz bands. The lower-band antenna consists of four modified quarter-mode substrate-integrated waveguide elements, which are excited in-phase and with same magnitude to obtain vertically polarized omnidirectional radiation. The upper-band antenna is based on a four-port square patch with differential feeds 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 an overall size of 90 × 90 × 3.66 mm
$^3$
(0.735
$\lambda$
× 0.735
$\lambda$
× 0.03
$\lambda$
at 2.45 GHz) was fabricated and measured. The 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.