Dual-Polarized Spline-Loop Antenna Array With Tilt Angle Radiation for 5G Base Stations

This paper introduces a dual-polarized spline-loop antenna element and array. The antenna element consists of two pairs of cross spline-ring dipoles, each with four thin metal strips connected to the adjacent dipole arms, serving as antenna radiators. These radiators resonate within the frequency band n78 (3300-3800 MHz). To achieve one wavelength resonance, the radiators are designed as spline-loop to increase the resonant path. Each spline-loop is fed by an integrated balun connected to a
$50~\Omega $
SMA. The thin strips connect the ends of the spline-ring dipoles to form a full-wave spline-loop. An integrated balun circuit is utilized to improve impedance matching and enhance the antenna’s operating bandwidth (approximately 36%). Moreover, to fulfill the electrical down-tilt range of 0 to 10 degrees for the 4-element dual-polarized antenna array used in base stations, a series-connected 4-way power divider is incorporated into the feed network. Each output Port of the power divider has a phase difference of 45 degrees, thereby inducing beam steering effects for the antenna array. Based on actual measurement results, the operating bandwidth of this antenna array covers the range of 2740 to 3910 MHz (approximately 34%), with isolation of 15 dB or greater, an electrical down-tilt of 10 degrees, and an antenna gain of approximately 11 dBi.