A millimeter-wave wideband antenna is presented for the 5th generation applications. The operation band ranges from 24 GHz to 39 GHz which covers most of the Ka band. Furthermore, a
With the rapid development of the wireless communication technology and increasing demand of the flexible applications, the next generation (5G) communication has become one of the hottest topics of the antenna industry [
As one of the most important technologies of 5G communication, multiple-input-multiple-output (MIMO) technology is widely applied due to the high transmission rate and stable communication quality. It uses multiple antennas for transmitting and receiving signal in the wireless communications; thus, it can improve the capacity of the communication system and the utilization ratio of spectrum without increasing the transmitting power. As the miniaturization of the electronic equipment has become the major trend with the technology evolution, it requires the antenna with multiple elements to be placed in a limited area. At the same time, the MIMO system requires high isolation between different antennas, which in turn, needs more space between antennas [
In current wireless communications, the
In this paper, we present a novel wideband antenna for the 5G communications. The operation band of the proposed antenna ranges from 24 GHz to 39 GHz. Using symmetrical structure, the proposed antenna realizes stable radiation pattern in such a wide band. Based on it, the MIMO antennas are proposed and studied. Due to its unique structure, the high isolation between antenna elements is maintained when applying to large scale array.
The proposed antenna is printed on a Rogers 4003C substrate with a relative permittivity of 3.4. The overall dimension of the proposed antenna is
Top (a) and bottom (b) of the proposed antenna.
Dimensions (mm) of the proposed antenna.
1 | 1.5 | 1.5 | 3.5 | 6.8 | 4.5 | 2 |
The proposed antenna is developed from the normal monopole antenna. The radius of the outer circle is set as 6.8 mm. Therefore, the length of the longest branch is 11.1 mm which is close to the wavelength in free space at 26 GHz. The bended structure is used for minimizing the overall size of the antenna. The inner arc with a radius of 3.5 mm is added on the longest branch; therefore, the length of the inner arc is 8.9 mm which is close to the wavelength in free space at 32.5 GHz. The directions of the inner and outer arcs are opposite which can weaken the affection between two arcs. Furthermore, another same structure is added because the symmetrical structure can benefit the radiation performance such as radiation pattern and peak gain. To enhance the resonant at higher frequencies, the slots with the width of 0.2 mm are added on the inner circle branches. As shown in Figure
(a) Return loss of the proposed wideband antenna with and without branches, (b) parametric study of the small cuts on the ground plane.
Since the S11 is unsatisfactory at higher frequencies, two interleaved branches are added as parasitic elements on the both sides of the antenna for introducing the resonances at higher frequencies. The distance between the parasitic elements and the main structure is set as 1 mm to make sure that the parasitic branches can couple energy from the port. The length of the longest branch of the parasitic elements is 9.1 mm which is close to the wavelength in free space at 33 GHz.
The ground plane of the proposed antenna is designed as a ring. This is because the structures on the top side are mostly circular; other geometries will introduce unnecessary capacitances and inductances which lead to a deterioration of bandwidth. In the center of the substrate, a via hole is added for feeding. Considering the dimensions of the 2.92 mm K connector which can operate at up to 40 GHz, the radius of the via hole is set as 0.5 mm and the inner radius of the ground plane is set as 2 mm. Furthermore, the slots are etched on the ground plane for improving the impedance matching. After the parametric study shown in Figure
Using HFSS, the return loss of the proposed antenna with and without branches are presented in Figure
The simulated radiation patterns are given in Figure
Simulated radiation patterns of the proposed antenna on the xoz-plane (a) and yoz-plane (b), simulated gain of the proposed antenna (c).
To investigate the potential in applying into various cases, the MIMO antennas with different distribution are studied. The geometry and simulated active S-parameters are presented in Figures
(a) Geometry and (b) simulated active S-parameters of the MIMO antenna with different angel between two elements.
To further investigate the mutual coupling between antenna elements, the current distribution on the MIMO antenna has been simulated and presented in Figure
Surface current distribution on the MIMO antenna at (a) 26 GHz and (b) 34 GHz.
Besides, due to the symmetry of the proposed antenna, the maximum value of the radiation pattern is on the plane which is perpendicular to the antenna. Hence, at 26 GHz, the radiation is mainly provided by the long branches on the
Based on the above antenna, a
(a) Geometry and (b) S-parameters of the
The simulated three-dimension (3-D) radiation patterns are illustrated in Figure
Simulated 3-D radiation patterns of the
In order to verify the designed approaches, a
Top (a) and bottom (b) view of the fabricated
The measured S-parameters are presented in Figure
Measured S-parameters of the fabricated MIMO antenna.
During the radiation pattern measurement, one antenna is excited while the other ones are attached to a 50 Ω load. Note that here, the terminations are only connected to the nearest neighbors since the influence from the distant ones is low enough to be ignored. The measured radiation patterns are presented in Figure
Measured radiation patterns of the proposed antenna on the (a) xoz-plane and (b) yoz-plane; (c) measured radiation efficiency and fitted curve of the antenna.
To highlight the merits of the proposed MIMO antenna, the comparison between our design and other typical compact MIMO antenna counterparts is given in Table
Characteristic parameters of the typical antenna counterparts.
Source | [ |
[ |
[ |
[ |
This paper |
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Total size (mm) | |||||
Number of ports | 2 | 4 | 2 | 4 | 81 |
Operating band (GHz) | 29.7-31.5 | 31-40.3 | 27-32 | 26-31 | 24-36 |
Min isolation (dB) | 25 | 21 | 37.1 | 21 | 20 |
Peak gain (dBi) | 8.6 | 11 | 17.9 | 10 | 7.8 |
Edge to edge spacing ( |
The total active reflection coefficient (TARC) is calculated to predict the radiation performance of the MIMO antenna. The TARC can be obtained from the scattering matrix by using the following formula:
TARC of the proposed MIMO antenna.
Moreover, as an important parameter of the MIMO antenna, the enveloped correlation coefficient (ECC) is computed to quantify the isolation among the MIMO antenna elements:
Correlation coefficient and diversity gain of the proposed UWB MIMO antenna.
Furthermore, the diversity gain of the proposed MIMO antenna is calculated and presented in Figure
In Figure
Finally, as another important parameter to evaluate the MIMO antenna performance, the multiplexing efficiency is calculated by using the formula as follows:
Multiplexing efficiency of the proposed UWB MIMO antenna.
In this letter, a wideband MIMO antenna with high isolation is proposed and studied. Due to its unique structure, the proposed antenna can achieve high isolation (under −20 dB) within an extreme closed space (0.4 mm) without any extra decoupling structure. Also, the simulated results show that the proposed antenna structure can be composed into different MIMO antenna structure as needed. The experimental results show that the proposed antenna has obvious advantages such as stable radiation pattern, wide operation bandwidth, and high isolation. The proposed antenna has potential applications in the next generation communication.
No data were used to support this study.
The authors declare that there is no conflict of interest regarding the publication of this paper.
This work was supported in part by the National Natural Science Foundation of China (Grant Nos. 6147109, 61611130067, and 61531010).