Embedded Design of Compact Broadband Omnidirectional Antenna With Quad-Polarization Diversity

A compact and broadband omnidirectional antenna is proposed for quad-polarization diversity. Novel reconfigurable structures of omnidirectional vertical polarization (VP) and horizontal polarization (HP) elements based on embedded design are put forward to achieve low-profile. A simplified equivalent LC cascaded circuit is modeled to better understand the broadband VP element and guide its design. In order to realize quad-polarization diversity, an advanced switchable feed network, which contains ten p-i-n diodes with four output states are carefully designed. Measured results show that the overlapped bandwidth for all operation modes is 20.5% (2.28-2.8 GHz) within a compact size of 0.69 λ0× 0.69 λ0× 0.064 λ0, where λ0is the free-space wavelength at the center frequency 2.5 GHz.