Page 120 - IJEEE-2023-Vol19-ISSUE-1

116 | Neamah, Al Sabbagh, & Al-Rizzo

The isolation is enhanced when the second patch antenna is the antenna system has a high diversity gain (DG>9.99 dB)
placed on the right instead of the first antenna, which is set over the frequency range, producing a good performance.
on the left. The surface current flows in opposite directions
in the orthogonal antenna because of the inconsistency of 10.00 0.030 0.015
closed adjacent geometry antenna elements, especially for
(left-right) layout; thus, this causes high isolation. This 9.99 0.025 0.012
approach introduces self-decoupling by surface current and
improves antenna isolation. Figure 10 shows the 3D 9.98 D.G 0.020 0.009
radiation pattern over the response band at different 9.97 ECC (3D) 0.015
frequencies. As shown in figure 10, the 3D radiation pattern ECC (S-parameters)
MIMO antenna is simulated at frequencies 4, 5.5, 0.006
8.5,18,24,28 and 38 GHz. The complementary pattern of the
two ports can be seen over the whole frequency response 9.96 0.010
band.
9.95 0.003

0.005

III. PERFORMANCE OF PROPOSED MIMO ANTENNA 9.94 0.000

0.000

9.93
3 6 9 12 15 18 21 24 27 30 33 36 39 42
Frequency (GHz)

MIMO technology provides a new degree of freedom Fig.11: Envelope correlation coefficient (ECC) in both
S-parameters and radiation pattern, including diversity gain
for wireless data communications and greatly enhances data (D.G) versus frequency.

transmission. The envelope correlation coefficient (ECC),

diversity gain DG, mean effective gain MEG and total active

reflection coefficient TARC are evaluated and presented to The MEG is an important MIMO parameter investigated in
this study. The MEG can define as the ratio of the average
confirm the proposed MIMO antenna's diversity capability. power received from the test antenna in the same
environment to the average power obtained by a reference
The ECC is applied to determine the antenna element antenna. The ideal MEG value should fall between -3 and
-12 dB for each. Equation (6) can be used to calculate
correlation. Law correlations between the antenna elements MEG[27].

should be used to achieve greater diversity between the

MIMO antenna elements. Acceptable ECC limits fall within

a range of a maximum is 0.5 and may be calculated using

Equation (3)[24] . åMEG(i ) = 0.5æç1-n 2ö
÷
S 1*1S à + S 2*1S à 2 S ij (6)
12 22
( )( )ECC = re = (3) è j =1 ø
1- ( S11 2 - S 21 2 ) 1- ( S 22 2 - S12 2 )
Where n is number of antennas, and for two ports MEG can

be found by:

where S * and S * represent the imaginary components of S11 MEG(1) = 0.5- | S 11|2 - | S 12 |2
11 21

and S21 parameters, respectively. S à and S à are real parts of MEG(2) = 0.5- | S 21|2 - | S 22 |2
12 22
Furthermore, the ratio of MEG1/MEG2 is less than 3 dB for
the S11 and S21 parameters, respectively. the optimal result to ensure good performance. Figure 12
shows the calculated MEG1, MEG2, and MEG1/MEG2. As
For a more precise calculation, we can calculate ECC by shown in figure 12, EMG1 and EMG2 are close to the
optimal value, which is -3dB, while their ratio is almost 0
using the far field, which is given by Equation (4)[25]: dB, which implies conforming with optimal MIMO
conditions.
ECC (re ) = | òò 4p[R1(q , F).R 2(q , F)d W] |2 (4)
| 4p | R 2(q , F) 1
òò 4p R1(q , F) |2 d Wòò |2 d W

where Ri (#, Ø) denotes the radiation pattern when port (i) is 0
activated, and ? denotes the solid angle.
-1
The following approximate expression is used to calculate MEG 1

the diversity gain as given in Equation (5)[26]. -2 MEG 2
MEG1/MEG2
DG = 10 1- ( re )2 (5) MEG (dB)
-3

Figure 11 depicts the ECC calculated with two methods; one -4
is by using S-parameters, and the second is by using far-field
versus frequency; also, DG is included in this figure. As -5
shown in figure 11, the ECC<0.001 we get by S-parameters
and ECC<0.007 by far-field shows outstanding system -6
performance from 3.6 GHz to over 40 GHz. This result is 3 6 9 12 15 18 21 24 27 30 33 36 39
quite less than the lime of MIMO condition. Furthermore, Frequency (GHz)

Fig. 12: Simulated mean effective gain MEG1, MEG2 and
MEG1/ MEG2 versus frequency of the super-UWB-MIMO
antenna.