2012 IEEE Asia-Pacific Conference on Antennas and Propagation, August 27-29, 2012, Singapore
Two UWB-MIMO antennas with high isolation using sleeve coupled stepped impedance resonators Yingsong LI, Wen xing LI, Chengyuan Liu, Tao Jiang College of Information and Communications Engineering, Harbin Engineering University, Harbin, Heilongjiang, 150001, CHINA
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[email protected] Abstract— Two printed ultra wideband (UWB) antennas integrated with stepped impedance resonators for Multiple Input Multiple Output (MIMO) communications applications are proposed in this paper. The proposed MIMO antennas consist of two simple printed microstrip-fed monopole antennas. The high isolations are obtained by using sleeve coupled rectangle stepped impedance resonator (R-SIR) and sleeve coupled roundness stepped impedance resonator (RD-SIR) on the ground plane, respectively. The proposed antennas operate over a wide impedance bandwidth ranging from 3.1GHz to 10GHz. And the antennas have high isolation over 23dB. The return loss and the isolation of the antenna are investigated by means of HFSS. The results show that the proposed UWB-MIMO antennas have high isolation and good impedance match characteristic.
having high isolation and good impedance bandwidth, which is good candidate for UWB-MIMO communications systems. II.
GEOMETRY STRUCTURE OF PROPOSED ANTENNAS
The proposed UWB MIMO antennas are illustrated in Fig.1. Fig.1 (a) is a UWB-MIMO antenna integrated with R-SIR and Fig.1 (b) is a UWB MIMO antenna incorporated with RD-SIR. The proposed diversity UWB MIMO antennas are printed on a substrate with relative permittivity of 2.65, a loss tangent of 0.002 and a thickness of h=1mm. The proposed diversity UWB MIMO antennas consist of two microstrip-fed square
Keywords-UWB antenna, MIMO antenna, steeped impedance stub, high isolation, stepped impedance resonator
I.
INTRODUCTION
With the development of wireless communications, the capacity is getting embarrassed. A lot of method has been proposed to increase capacity of existed systems. One of the most effective technologies Multiple Input Multiple Output (MIMO) has been proposed and studied widely [1]. MIMO antenna is a key part of MIMO system. A good MIMO antenna can not only improve the characteristic of MIMO system but also reduce the coupling between the multiple antennas. For this reason, plenty of MIMO antennas for mobile communications have been investigated recent years [2-6]. However, most of the proposed MIMO antennas have narrow impedance bandwidth and low isolation. In addition, a lot of slots are etched on ground plane. The slots leak electromagnetic waves which deteriorate the radiation patterns of MIMO antenna. And most of proposed MIMO antennas have complex isolation units which are difficult to redesign. In this paper, two novel high isolation antenna structures based on simple square UWB antenna have been proposed and analyzed. The proposed MIMO diversity antenna structures consist of two simple microstrip fed square patch UWB antenna with limited partial ground plane. The high isolations are achieved by using sleeve coupled rectangle stepped impedance resonator (R-SIR) and sleeve coupled roundness stepped impedance resonator (RD-SIR) on the ground plane, respectively. The proposed antennas are investigated using high frequency structure simulator (HFSS) based on finite element method (FEM). The impedance bandwidth and isolation are given in this paper. The results show that the proposed MIMO antennas,
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(a) UWB MIMO antenna 1 with sleeve coupled SIR L1
W1
R
g1 L3
g
W2 L
W (b) UWB MIMO antenna 2 with sleeve coupled UIR Fig.1 Geometries of proposed UWB-MIMO antenna
patch antennas based on[5], R-SIR, RD-SIR and partial ground plane. III.
dimension of the coupling gap between sleeve and the R-SIR and RD-SIR. The dimension of SIR and UIR can also improve the isolation of the proposed UWB-MIMO antennas.
RESULTS AND DISCUSSIONS
In this section, the proposed two UWB-MIMO antennas are investigated by means of HFSS. The return loss and the isolation of the UWB-MIMO antennas are demonstrated herein. The parameters are optimized as follows: L=24mm, W=62mm, L1=13mm, W1= 13mm, W2=36mm, L3=3mm, g=1mm, L2=4mm, W3= 4mm, g1=0.5mm, R=2.4mm. Fig.2 shows the return loss curves of proposed diversity antennas. From Fig.2, the proposed UWB-MIMO antennas with SIRs have very wide impedance bandwidth ranging from 3.1GHz to 10GHz. And the proposed UWB-MIMO antenna without SIRs has a little mismatching at low frequency. This is caused by the mutual coupling between the two UWB antennas.
Fig. 4 Radiation patterns of proposed UWB-MIMO antennas The radiation patterns of the proposed UWB-MIMO antennas at 5GHz and 8GHz are given herein. The port 1 is exited and the port 2 is terminated with a 50Ω load impedance. It can be seen from Fig.4 that the radiation patterns in the operation band are stable. The proposed UWB-MIMO antennas have a nearly omni-directional radiation patterns in H-plane and a monopole-like radiation patterns in E-plane. IV.
Fig. 2 Return loss of proposed UWB-MIMO antennas Fig.3 demonstrates the isolation of the proposed UWBMIMO antennas. It can be seen from the Fig.3 that the isolation of the proposed UWB-MIMO antennas can be improved by using the R-SIR and RD-SIR. In this paper, the proposed UWB-MIMO antennas have a high isolation which can reach 23dB. The isolation can also be changed by controlling the
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[2]
[3]
[4]
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Fig. 3 Isolation of proposed UWB-MIMO antennas
CONCLUSION
In this paper, two diversity UWB-MIMO antennas integrated with stepped impedance resonators are proposed and discussed. The designed UWB-MIMO antennas have wide bandwidth ranging from 3.1GHz to 10GHz. A sleeve coupled R-SIR and a sleeve RD-SIR are employed in the ground plane to obtain high isolation. The return loss, isolation and radiation patterns are investigated and discussed in this paper. The simulation results show that the proposed UWB-MIMO antennas can achieve a high isolation which is beyond 23dB. The proposed UWB-MIMO antennas can well meet the requirement of MIMO wireless communication applications. The isolation improvement technology will be studied further to obtain high gain and small size.
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