Annulus-Shaped ±45°-Polarized Antenna With Broad Band and Enhanced Gain and Isolation

A high-gain, high isolation, and broadband design of ±45°dual-polarized antenna is presented. It starts from a simpler single-polarized printed circuit board (PCB) dipole antenna with a pair of 1/4 wavelength arms and a ~1/4 wavelength balun. The arms of the dipole antenna are then curved into a 1/4 circular arc-alike patch, and four dipole antennas are joined, end to end and with gaps between each other, to make an annulus-shaped radiation aperture with a pair of +45°-polarized dipoles and a pair of -45°-polarized dipoles. Finally, both +45°-pair and -45°-pair are, individually, merged into a +45°-port and a -45°-port of the proposed antenna through a micro-strip combiner on top side of the bedframe. Besides, the choke technique is also employed in this design to ensure low cross-band scattering in multi-band and multi-array applications. Over a broad working band of 698–960 MHz this design achieves VSWR < 1.5, gain of 9.5-11.3 dBi, and well isolation of > 26 dB.