Compact triple - Band mimo antenna with high isolation for handheld application

hout double rectangular DGS structures is 
 shown in Figure. 4. 
 Figure 4. The reflection coefficient of antenna with 
 and without double rectangular DGS structures. 
 It is clearly seen that three resonant 
 frequencies are obtained. These are 2.4 GHz, 
 3.5 GHz and 6.3 GHz which covers Wi-Fi, 
 LTE/Wimax and C-band satellite band. 
 Reflection coefficients of the proposed antenna 
 are -26.44 dB, -42.87 dB, and -30.5 dB at 
 (a) (b) resonance frequencies of 2.4 GHz, 3.5 GHz, 
 and 6.3 GHz with the bandwidth of 201.8 MHz, 
 540 MHz, and 159.7 MHz respectively. By 
Figure 3. The slot loaded structure (a) double square applying DGS structure to ground plane, 
 shape (b) periodic rectangular shape. several parameters of antenna are improved 
 Table 2. Detail dimensions of MIMO antenna such as 100 MHz bandwidth enlarger at 3.5 
 GHz as shown in Figure 4, radiation efficiency 
 Value Value 
 Parameter Parameter and gain improvement as shown in Table 3. 
 (mm) (mm) 
 df 23.8 c1 21.05 Table 3. The comparison radiation efficiency and 
 de 4 c2 0.5 gain of single antenna with and without DGS 
 w1 20.1 c3 8.85 
 Frequency (GHz) 2.4 3.5 6.3 
 w2 20.6 c4 0.9 With 
 Radiation 99.94 99.6 93.55 
 a1 2 c5 0.5 DGS 
 Efficiency 
 a2 1 d1 2.4 Without 
 (%) 98.51 98.35 81 
 b1 3.4 d2 0.5 DGS 
 With 
 b2 0.5 d3 0.5 3.06 4.1 6.34 
 DGS 
 Gain (dB) 
 b3 0.5 d4 0.45 Without 
 2.95 4.1 5.45 
 DGS 
 D.T.T. Tu et al. / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 33, No. 1 (2017) 47-56 51 
 145.9 MHz at 2.4 GHz, 3.5 GHz and 6.3 GHz 
 respectively due to the mutual coupling. 
 (a) At 2.4 GHz 
 Figure 6. The S parameters of MIMO antenna with 
 distance from feed to feed is 0.5 at 6.3 GHz. 
 (b) At 3.5 GHz 
 (a) At 2.4 GHz 
 (c) At 6.3 GHz 
 Figure 5. The 2D radiation pattern 
 of DGS single antenna. 
 2D radiation patterns for the three bands of (b) At 3.5 GHz 
proposed antenna are illustrated in Figure 5 (a-c). 
It is clear that the antenna get the smooth and high 
directive 2D patterns. Besides, at all bands of 
interest, the antenna gets high radiation efficiency 
of over 93% as well as high gain. 
3.2. MIMO Antenna 
 The S parameters of MIMO system are 
shown in Figure 6 with the distance of 4 mm. It is 
clearly seen that the S12 of all bands are higher -
 (c) At 6.3 GHz 
20 dB because of close distance. In addition, the 
bandwidths of antenna at all three bands are Figure 7. The 2D radiation pattern 
decreased and get 202.6 MHz, 341.7 MHz and of MIMO antenna. 
52 D.T.T. Tu et al. / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 33, No. 1 (2017) 47-56 
 The 2D radiation patterns also have Moreover, by applying DGS structure to the 
distorted their shape as shown in Figure 7. ground, the performances of several MIMO 
However, the antenna still gets the smooth and antenna parameters are improved. Firstly, the 
high directive 2D patterns. In addition, the bandwidths of MIMO antenna at all three bands 
gains are better at 2.4 GHz and 3.5 GHz thanks are increased. Especially at 3.5 GHz, the 
to structure of array antenna. bandwidth get 573.5 MHz which is enlarged 
 To reduce the mutual coupling between two 231 MHz. Then, the total efficiency and gain of 
antenna element at this close distance, two “slot antenna are also improved lightly as shown in 
and variation” DGS structures with 8-shape and Table 4 while the 2D radiation patterns at 
periodic loop shape are proposed. Recently, interest bands are the same with smooth shape. 
DGS structure is one of techniques that widely 
is used in MIMO antenna designs to improve 
isolation between antenna elements because this 
structure uses the dielectric as a band gap 
structure to suppress mutual coupling as well as 
to get a more compact size. However, almost 
previous DGS studies have achieved a low 
mutual coupling for flat antenna structure 
whose height and substrate are the same. A few 
researches focus on MIMO PIFA antennas but 
only apply to single or dual band ones. As 
illustrated in Figure 9, the proposed “slot and 
variation” DGS structure with 8-shape and Figure 9. The S parameters of MIMO antenna with 
periodic loop shape makes three stop-bands that and without slot and variation DGS structures at the 
is able to suppress mutual coupling for distance of 4 mm from edge to edge. 
triple-band MIMO antenna. This structure is Table 4. The comparison radiation efficiency and 
also useful for triple-band MIMO PIFA gain of MIMO antenna with and without “slot and 
antenna. The Figure 10 shows the S parameters variation” DGS structure 
of the MIMO antenna using the “slot and 
 Frequency (GHz) 2.4 3.5 6.3 
variation” DGS structures for close distance of 
 With 
4 mm (0.032 at 2.4 GHz) from edge to edge. It 92.9 93.3 90.4 
 Total DGS 
is clearly seen that the mutual coupling of Efficiency 
 Without 
MIMO antenna using slot and variation DGS (%) 88.6 86.1 90.4 
structures is decreased, especially at 3.5 GHz. DGS 
 With 
Besides, the proposed MIMO antenna gets the 3.58 4.54 6.12 
 DGS 
high isolation between antenna elements (S12 Gain (dB) 
around -20 dB) at all three bands. Without 
 3.5 4.24 5.84 
 DGS 
 In MIMO antenna system, correlation 
 factor, which is so-called enveloped correlation 
 coefficient (ECC), will be significantly 
 degraded with higher coupling levels. The 
 factor can be calculated from radiation patterns 
 or scattering parameters. For a simple two-port 
 network, assuming uniform multipath 
 Figure 8. The S12 parameters of decoupling 
 structure using “slot and variation” DGS. environment, the enveloped correlation ( ), 
 D.T.T. Tu et al. / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 33, No. 1 (2017) 47-56 53 
can be calculated conveniently and quickly coupling and previous researches. It is obvious 
from S-parameters as follows [17]: that the proposed antenna gets S12 parameters 
 under -20 dB to meet the isolation demand of 
 (3) good MIMO antenna [18] for all three bands 
 while distance from edge to edge is much closer 
 The correlation factor curves of the than all previous studies. Besides, the other 
proposed MIMO antenna at three bands are parameters such as -10 dB bandwidth and 
shown in Figure 11. From this figure, the triple- efficiency are better. 
band PIFA MIMO antenna using “slot and 
variation” DGS structure has the simulated 
ECC lower than 0.01 for three interest bands. 
Therefore, it is quite suitable for mobile 
communication with a minimum acceptable 
correlation coefficient of 0.5 [16] as well as for 
LTE equipments with value of   0.3 for the 
bands of interest [17]. 
 Table 5 shows comparison between our 
triple-band MIMO antenna using “slot and Figure 10. Correlation Factor  12 curve for the 
variation” DGS structure to get low mutual proposed MIMO antenna.
 Table 5. The comparison between present design and previous researches 
 Mutual 
 Distance 
 Patch size coupling 
 Resonant Ground -10 dB from Radiation 
 at low at Gain 
 Frequency size Bandwidth edge to efficiency 
 frequency resonant 
 edge 
 frequency 
 2.45 GHz 4% -14 dB 3.34 dBi x 
 Ref 15.6 x 10 x 50 x 100 18.8 
 5.25 GHz 3.84% -12 dB x x 
 [10] 4 mm3 mm2 mm 
 5.775 GHz 2.6% -13 dB x x 
 2.45 GHz 5.1% -15 dB 4.5 dBi 93% 
 Ref 3.5 GHz 11.5 x 13.8 50 x 100 2.857% -22 dB 4.12 dBi 90% 
 27 mm 
 [11] 5.2 GHz x 4 mm3 mm2 2.4% -21 dB 6.07 dBi 86% 
 5.75 GHz 3.65% -19.5 dB 5.9 dBi 87% 
 1.77 GHz 10 x 31 x 0% -7 dB 0.5 dBi 48.9% 
 Ref 7.86 GHz 4.5 mm3 40 x 100 0% -31 dB 3 dBi 77.2 % 
 22 mm 
 [12] 2.02 GHz 8 x 27 x mm2 8% -6.8 dB 0.9 dBi 45.5 % 
 8.89 GHz 4.5 mm3 0% -28 dB 1.75 dBi 71.39% 
 780 MHz 0% -31dB x 
 Ref 9.75x17 x 50 x 100 
 1.8 GHz 2.78% -11 dB 16 mm 1.8 dBi x 
 [13] 6.4 mm3 mm2 
 3.2 GHz 9.3% -11 dB x 
 900 MHz 6.8 % -15 dB 1 dBi x 
 Ref 1.8 GHz 25.7 x 17 x 80 x 100 13 % -16 dB 3.5 dBi x 
 144 mm 
 [14] 2.6 GHz 0.8 mm3 mm2 27 % -18 dB 3.2 dBi x 
 3.5 GHz 4.2 % -40 dB 1.5 dBi x 
 2.4 GHz 9.17 % -20 dB 3.58 dBi 92.9% 
 Our 19.6 x 19.8 37 x 43.6 
 3.5 GHz 16.39 % -20 dB 4 mm 4.54 dBi 93.3% 
 design x 6 mm3 mm2 
 6.3 GHz 2.7 % -22 dB 6.12 dBi 90.4% 
 L 
54 D.T.T. Tu et al. / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 33, No. 1 (2017) 47-56 
4. Measurement results 
 To verify the performance of the proposed 
triple-band PIFA antenna, the antennas are 
fabricated with single and MIMO model on 
FR4 substrate with the thickness of 1.6 mm. 
 (a) Top view (b) Bottom view 
 Figure 13. Fabricated triple-band 
 MIMO PIFA antenna. 
 (a) Top view (b) Bottom view 
 Figure 11. Fabricated single triple-band PIFA. 
 Figure 14. Measured and simulated results of S 
 parameter of the proposed MIMO PIFA antenna. 
 The measured results of S parameters are 
 compared to simulation ones in Figure 15. It is 
 clearly seen that the MIMO antennas operate at 
 2.4 GHz, 3.5 GHz and 5.7 GHz with over 10%, 
 20% and 5% bandwidth, respectively. The 
 Figure 12. Measured and simulated results of S11 mutual coupling at all interest bands are under -
 parameter of the proposed single PIFA antenna. 20 dB. It can be concluded that the measured 
 Figure 12 shows a photography of single results agree well with the simulated ones. 
antenna with total compact size of 37 x 19.8 x 6 Thus, using the proposed “slot and variation” 
mm3. The measured result of S11 parameter is DGS structures can reduce the mutual coupling 
compared to simulation one in Figure 13. It is between antenna elements in triple-band MIMO 
clearly seen that the single antenna operates at antenna to ensure the isolation demand of good 
three bands of 2.4; 3.5 and 6.3 GHz with MIMO antenna. 
10.5%, 27.5% and 4% bandwidth, respectively. 
 The proposed triple-band MIMO antenna 5. Conclusion 
using “slot and variation” DGS structure is 
fabricated on the FR4 substrate as shown in In this paper, a compact triple-band MIMO 
Figure 14. The antenna gets compact in size of PIFA antenna using U-shape slots as well as the 
 coordinate double rectangular with the “slot 
37 x 43.6 x 6 mm3. 
 D.T.T. Tu et al. / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 33, No. 1 (2017) 47-56 55 
and variation” DGS structures is proposed. The Progress In Electromagnetics Research C, vol. 
total MIMO antenna occupies a small area of 37 67, pp. 153–164, 2016. 
x 43.6 mm2 on the FR4 substrate. The MIMO [5] Mustapha El Halaoui et al., “Dual Band PIFA 
antenna gets the large bandwidths which are for WLAN and WiMAX MIMO Systems for 
 Mobile Handsets,” 9th International 
220 MHz, 573.5 MHz and 170 MHz at 2.4 Conference Interdisciplinarity, Tirgu-Mures, 
GHz, 3.5 GHz and 6.3 GHz respectively. The Romania, pp. 878-883, October 2015. 
proposed MIMO PIFA antenna has solved the [6] Do-Gu Kang, Jinpil Tak, and Jaehoon Choi, 
narrow bandwidth limitation of conventional “MIMO Antenna with High Isolation for 
PIFA. In addition, using novel DGS structures, WBAN Applications,” International Journal 
the antenna not only gets the extremely high of Antennas and Propagation, Volume 2015, 
radiating efficiency of more than 90% for all Article ID 370763, 7 pages, 2015. 
bands but also gets the high gain of the antenna [7] Ajinkya Vekhande, Ajinkya Joshi, Madhur 
which is respectively 3.6 dB, 4.55 dB and 5.86 Kapse, Sagar Lohit, Yashashree Bhange, 
 “Dual Band Print Antenna for Wireless 
dB at 2.4 GHz, 3.5 GHz and 6.3 GHz operating Applications with Enhanced Isolation,” Int. 
frequency, respectively. Besides, the MIMO Journal of Engineering Research and 
antenna has ensured the mutual coupling Applications, vol. 5, no. 4, pp. 82-84, 2015. 
between antenna elements under -20 dB for all [8] Majid Manteghi and Yahya Rahmat-Samii, “A 
three bands with the narrow distance of 4 mm. Novel Miniaturized Triband PIFA for MIMO 
This proposed antenna is suitable for handheld Applications,” Micowave and Optical 
terminals of Wi-Fi, Wimax/LTE and C-band Technology Letters, vol. 49, no. 3, pp. 724-
 731, 2007. 
satellite applications. 
 [9] Rashid Ahmad Bhatti, Jung-Hwan Choi, and 
 Seong-Ook Park, “Quad-Band MIMO 
 Antenna Array for Portable Wireless 
Acknowledgments Communications Terminals,” IEEE Antenna 
 and Wireless propagation Letters, vol. 8, pp. 
 This work is partly supported by Motorola 129-132, 2009. 
Solutions Foundation under Motorola [10] K. Zhao , S. Zhang, and & S. L. He, “Closely-
scholarship and research funding program for Located MIMO Antennas of Tri-Band for 
 WLAN Mobile Terminal Applications,“ 
ICT education. Journal of Electromagnetic Waves and 
 Applications, vol. 24, pp. 363–371, 2010. 
 [11] J. Jasper Sweetlin, T. Anita Jones Mary, “Mutual 
References Decoupling in Quad Band MIMO Slotted PIFA for 
 Wireless Applications,” The International Journal 
 [1] Hang Wong, Kwai-Man Luk, Chi Hou Chan, of Engineering and Science (IJES), vol. 1, no. 2, 
 Quan Xue, Kwok Kan So, Hau Wah Lai, “Small pp. 303-307, 2012. 
 antennas in Wireless Communications,” [12] Jianfeng Zhu, Botao Feng, Li Deng, Biao 
 Proceedings of the IEEE Journal, vol. 100, no 7, Peng, and Shufang Li, “Coupled-Fed Tri-Band 
 pp. 2109-2121, 2012. MIMO Antenna for WWAN and LTE 
 [2] Rowell, C., Lam, E.Y., “Mobile phone antenna Application,” Microwave and Optical 
 design,” IEEE Antennas and Propagation Technology Letters, vol. 59, no. 2, pp. 463-
 Magazine, vol. 54, no. 4, pp. 14-34, 2012. 468, February 2017. 
 [3] Murch, R.D., and Letaief, K.B., “Antenna systems [13] Duong Thi Thanh Tu, Nguyen Gia Thang, Vu 
 for broadband wireless access,” IEEE Van Yem, “A Triple-band PIFA Antenna 
 Communication Magazine, vol. 40, pp. 76-83, Design Using Defected Ground Structure for 
 2002. Handheld Applications”. International 
 Conference on Science and Technology, 
 [4] Ahmed A. Naser, Khalil H. Sayidmarie, and 
 pp.745-750, Nov 2016. 
 Jabir S. Aziz, “Compact High Isolation 
 Meandered-Line PIFA Antenna for LTE [14] J. Thaysen and K. B. Jakobsen, "Envelope 
 (Band-Class-13) Handset Applications,” correlation in (N, N) MIMO antenna array from 
56 D.T.T. Tu et al. / VNU Journal of Science: Comp. Science & Com. Eng., Vol. 33, No. 1 (2017) 47-56 
 scattering parameters," Microwave and Optical [16] 3GPP TS 36.101, V8.3.0. “EUTRA User 
 Technology Letter, vol. 48, pp. 832-834, 2006. Equipment Radio Transmission and 
 [15] M. P. Karaboikis, V. C. Papamichael, G. F. Reception,” September 2008. 
 Tsachtsiris, and V. T. Makios, "Integrating [17] Istvan Szini, Alexandru Tatomirescu, and Gert 
 compact printed antennas onto small Frølund Pedersen, “On Small Terminal MIMO 
 diversity/MIMO terminals," IEEE Antennas, Harmonizing Characteristic Modes 
 Transactions on Antennas and Propagation, with Ground Plane Geometry”, IEEE Antenna 
 vol. 56, pp. 2067-2078, 2008. Propag. Trans. On, vol. 63, no. 4, pp. 1487 - 
 1497, 2015. 
 p