A multi-port interconnected magneto-electric dipole antenna array for 5G applications

Zihao Chen¹, Wenxu Zhang¹, Kai-xu Wang¹

¹ College of Electronics and Information Engineering, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China

Email: wangkaixu@hit.edu.cn.

Introduction: The 5G communication has attracted more and more research passion from both academic and industry due to its advantages of high data rates, high reliability and low delay. Millimeter wave bands have abundant working spectrum for 5G communication compared with low-frequency bands, which helps to achieve high data rate [1]. The high propagation attenuation and multipath propagation in millimeter-wave band degrade the communication system performance. Dual polarized and circularly polarized antenna arrays with high gain and wide bandwidth are highly demanded to resolve this problem.

A lot of dual polarized and circularly polarized antennas are reported for 5G communication applications. Patch and slot are widely used in early researches [2]-[5]. A dual-band miniaturized e-shaped antenna with circular polarization at 28 and 38 GHz in [2]. An -10 dB impedance bandwidth of 18.42%, a maximal gain of 12.69 dBi and a 3dB axial ratio (AR) bandwidth of 1.65% are achieved with a 2×2 array. Dual-polarized cavity-backed bow-tie slot arrays are designed and integrated on the frame of the mobile handset in [3]. The 1×4 array can achieve a maximal gain of 12. 8 dBi and -10 dB impedance bandwidth of 4.28%. The bandwidth of these antennas is narrow and techniques are need to broaden their bandwidth.

Magneto-electric (ME) Dipole is a good antenna candidate for 5G communication applications due to its wide impedance bandwidth and stable unidirectional gain patterns. The magneto-electric dipole model with a significant impact was firstly proposed by Kwai-Man LUK in 2006 [6]. The dual polarized and circularly polarized ME dipole antenna are realized with the SIW feeding method in [7-8]. The two-layer SIW feeding network makes the design and fabrication complicated. A millimeter-wave dual-polarized ME-dipole antenna is reported in [9]. Two pairs of orthogonally oriented feed probes are used to feed the antenna. The antenna exhibits 50% impedance bandwidth, 17.8 dB port isolation, and up to 9.4 dBi gain. A circularly polarized differentially fed ME-dipole array is reported in [10]. It manages to achieve -10 dB impedance bandwidth of 32.2% with a broadside left-handed CP gain from 10.2 to 11.8 dBic. However, they lack of design flexibility to support different polarizations.

In this letter, we present a novel design of ME dipole antenna array for 5G applications and demonstrate its flexibility to configure the antenna to multiple antennas. We show that the antenna can be used as a balanced antenna, dual-polarized antenna, as well as a circularly polarized antenna through changing the amplitude and phase of the feeding ports. An interconnected ME dipole radiator is specially designed to achieve high gain without complex feeding network.

Antenna design and operating principle: The multi-port interconnected ME dipole antenna array is designed on a PCB substrate of Rogers 5880 with thickness of 1.57 mm, ε_r = 2.2 and tanδ=0.0009. The antenna radiator consists of four ME dipole elements. For each ME dipole element, four identical metallic patches are printed on the top of the substrate, which realize the electrical dipole. The inner edges of the metallic patches are shorted to ground through three metallic vias, which form the magnetic dipole together with the ground plane. Cross strips, which are fed by the vias at one end, are used to excite the antenna with the electric fields in the x-direction and in the y-direction. CPW lines are utilized to transmit energy between elements. The length of the CPW lines is specially designed to keep the current distributions of the ME dipole elements are in phase. The radiators are designed symmetrically in the x-direction and the y-direction to achieve symmetrical radiation performance when the antenna array radiates linearly polarized waves in the x-direction and the y-direction. The detailed dimensions of the proposed antenna array are listed in Table I. Four feeding ports on the cross strips are arranged on the cross strips to enlarge the design flexibility of the ME dipole antenna array. Port 1 and 4 can be configured as one balanced antenna which radiates polarized waves in the y-direction and ports 2 and 3 as another balanced antenna which radiates polarized waves in the x-direction. The current are orthogonal on the cross strips which results in low coupling level between two polarizations, which enables the propose multiport interconnected ME dipole antenna array to support the simultaneous reception in two polarizations or transmission in either polarization. Circular polarization can be realized as well by exciting the feeding ports with equal amplitude and a phase difference of 90^o.