The Fig. 2 (a) and (b) shows the effect of the dimensions of the radiating rectangular patch, quarter wave transformer feeding on the reflection coefficient and ports 1–4. Hence, the first resonant frequency is directly varied with the dimensions of the Antenna1. The antenna resonates at the centre frequency of 28 GHz. And the proposed antenna provides the VSWR is smaller than 2 for the entire operating band
The inset feeding is one of the popular techniques for perfect matching. The effect that "a" has on the reflection coefficient is seen in Fig. 3(a). When "a" is increased, the current path on the patches becomes lengthier. The frequency of the centre resonance frequency shifts to the right. We can say the resonant frequency is varied by "a." Both the centre frequency and the impedance bandwidth of the MIMO antenna are impacted when the width of the complementary split ring resonator (ws = e) is made wider. This is seen in Fig. 3(b).
The orthogonal arrangement of the radiating components of the proposed antenna assures that it will have good isolation. The variations in the antenna 2's s-parameter are seen in Fig. 4. Isolation of 35 dB and 45 dB is established between the radiating elements 1, 2, and 1, 4 correspondingly, and radiating elements 1 and 3 are separated by an isolation of 75 dB at all frequencies between 24 GHz and 34 GHz. The Current from radiating element 1 is prevented from flowing, resulting in high isolation.
The orthogonal arrangement of the radiating patches on the substrate of the proposed antenna assures that it will have good isolation. The variations in the antenna 2's VSWR simulated and measured are seen in Fig. 5. It can be observed that the axial ratio bandwidth of the proposed MIMO antenna is 1.5 GHz from 27.25 GHz to 28.75 GHz.
Table 3
A comparison between the reported works with proposed antenna.
Reference
|
Size
(mm×mm)
|
Ports
|
Impedance Bandwidth
(GHz)
|
Isolation (dB)
|
Circular Polarization Bandwidth
(GHz)
|
CLL
(bits/s/Hz)
|
ECC
|
Gain
(dBi)
|
1
|
39× 39
|
4
|
2.6, 3.5, 4.8, 5.8
|
21.5
|
-
|
0.4
|
0.012
|
-
|
2
|
30 × 30
|
1
|
3.23–6.26
|
> 20
|
2.95–6.02
|
0.078
|
0.02
|
-
|
3
|
50× 30
|
4
|
3300–4200 MHz
|
28
|
-
|
0.017
|
0.0000495
|
-
|
4
|
50 × 50
|
4
|
3.3–4.2
|
20
|
-
|
-
|
0.04
|
-
|
5
|
140 x 89
|
8
|
3.4–3.7
|
15
|
-
|
-
|
0.3
|
-
|
6
|
33 x 27.5
|
2
|
0.4
|
30
|
-
|
-
|
0.001
|
6.9
|
7
|
180 x 180
|
4
|
0.6–1.09
2.6–3.4 and 4.2-7.0
|
22
|
-
|
29.83
bps/Hz
|
≤ 0.50
|
6.54
|
8
|
50 x 50
|
8
|
2–12
|
17
|
-
|
0.5
|
0.3
|
3.15
|
9
|
75 x 180
|
64
|
3.2–4
|
11
|
-
|
-
|
0.005
|
2–5
|
10
|
40 x 3
|
64
|
3.3-5
|
21
|
-
|
-
|
0.11
|
-
|
11
|
50 x 100
|
4
|
2.7–3.6
|
25
|
-
|
-
|
0.009
|
5.5
|
12
|
27.3 x 1.2
|
8
|
3.4–3.6
|
15
|
-
|
-
|
0.16
|
4.5
|
13
|
20 x 20
|
2
|
27.5-28.35
|
24
|
-
|
-
|
0.013
|
8
|
15
|
150 x 75
|
8
|
3-5.5
|
15
|
-
|
31.6–39.2 bps/Hz
|
0.1
|
2
|
17
|
124 x 74
|
8
|
2.4–2.7
3.3–3.6
|
15.1
|
-
|
0.2
|
0.12
|
-
|
Proposed work
|
40 x 40
|
4
|
25.5–32.5
|
25
|
1.5
|
0.2
|
0.12
|
5
|
The envelope correlation coefficient is calculated [13], the TARC, and the diversity gain [15] are the metrics that are used for the purpose of evaluating the diversity offered by the proposed antenna. The ECC of a MIMO antenna is a technique for conducting an analysis of the degree to which nearby radiating components are correlated with one another. The diversity of a MIMO antenna may be measured by its ECC, which can be found in Fig. 9 and is determined by making use of the S-parameters in accordance with the Eq. (1).
$$\text{E}\text{C}\text{C}=\frac{{\left|{s}_{11}^{*}{s}_{12}+{s}_{12}^{*}{s}_{22}\right|}^{2}}{\left(1-\left({\left|{s}_{11}\right|}^{2}+{\left|{s}_{21}\right|}^{2}\right)\right)\left(1-\left({\left|{s}_{22}\right|}^{2}+{\left|{s}_{12}\right|}^{2}\right)\right)}$$
1
The Eq. (1) can be applied between any two antenna ports. For the proposed antenna, the ECC value of 0.12 is attained over the whole frequency spectrum in which it operates. If the ECC value is lower than the threshold level of 0.5 and Channel Capacity Loss value of 0.2 is attained over the frequency from operating range. Figure 10 displays a plot of the diversity gain is greater than the 9.9993 value over the antenna operating frequency, which can be computed with the help of the equation shown in [2].
$$DG=10\sqrt{1-{\left|ECC\right|}^{2}}$$
2
Figure 11 illustrates the proposed antenna gain plot, over the frequency band the antenna maintains the maximum gain of 5dBi.The total active reflection coefficient of the antenna is shown in figure 12. The fabricate antenna with front and rear views are shown in figure 13.