Fractal Loaded, Novel, and Compact Two- and Eight-Element High Diversity MIMO Antenna for 5G Sub-6 GHz (N77/N78 and N79) and WLAN Applications, Verified with TCM Analysis

Abstract

A novel compact fractal loaded two- and eight-element multiple input multiple output (MIMO) with strong diversity is designed for 5G Sub 6 GHz and WLAN applications. The suggested antenna is designed and manufactured on inexpensive FR4 dielectric material with small size of 72 mm × 72 mm × 1.6 mm (0.792λ × 0.792λ × 0.0176λ, where λ is calculated at a lower operating frequency). The proposed layout features a partially grounded, protruding T-shaped stub on the underside of the substrate and a set of fractally loaded circular patch antenna elements on the top. Four triangular slots on the substrate and a T-shaped stub on the ground are employed to produce good isolation over the intended bands. The proposed antenna has a frequency range of (3.3–6.0) GHz, making it compatible with the 5G sub-6 GHz bands and the WLAN band thanks to its high isolation of above 15 dB and good impedance matching characteristics. Good agreement is observed between the antenna results and the theory of characteristic mode analysis approach. The designed antenna is well suited for 5G sub-6 GHz and WLAN communication applications due to its low ECC (0.005), total active reflection coefficient (TARC) (−10 dB), mean effective gain (MEG) (−3 dB), and diversity gain (DG) (−10 dB), channel capacity losses (CCL) (0.05), peak gain (>2.5 dBi), radiation efficiency (>95%), and stable boresight radiation patterns.

1. Introduction

There is an increasing need for extremely high data rates and low latency and bandwidths in mobile device applications, largely due to the proliferation of wireless communication networks. Greater transmission rates (data rates), spectrum efficiency, and lower latency are just a few of the ways in which the next 5G mobile communication system improves upon the current 4G system. With a data rate 10 times that of 4G systems, 5G networks provide seamless interoperability and exceptional dependability [1,2,3,4,5,6]. MIMO technology powers 5G communication and improves data transfer rates and spectrum efficiency without requiring more transmission power or bandwidth. The close proximity of the antenna elements results in mutual coupling which can be improved by designing isolating elements between the closely spaced antennas [7]. Several research works have been conducted to improve the isolation between the antenna elements [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]. Use of a T-shaped narrow conducting strip [8], adoption of a common grounding branch as the decoupling structure between adjacent antennas [9], ACS-feed with an inverted L-shaped slot and a meander line structure [10], placement of MIMO arrays with a 90-degree phase shift with respect to each other [11], and placement of two antennas diagonally on either side of the antenna structure [12] are all examples of isolation techniques. The use of split-ring resonators (SRRs) of contrasting sizes [13], parasitic reflectors between radiating patches and protruded ground strips [14], T-shaped stubs between the radiators and rectangular-shaped protruded strips on the radiators [15], five electromagnetic band-gap (EBG) unit cells and two vertical slots between the two antenna elements [16], and etching a T-shape between the two antenna elements has been proposed [17,18].

Furthermore, various isolation enhancement techniques were proposed for four-element MIMO antenna systems in [19,20,21,22,23,24] which comprises a four-port MIMO antenna with a built-in circular-shaped isolator [19], defected ground technique [20], inserting a rectangular slot under each microstrip feedline of 4-element MIMO antenna [21], introducing an un-protruded multi-slot (UPMS) isolating element between two closely spaced antenna elements [22], cutting a rectangular slot under each microstrip feed line of 8-port 4-element MIMO antenna [23], and a rectangular parasitic structure carrying four circular patches between the adjacent and opposite radiators [24].

Later, in [25,26,27], various isolation strategies were presented for eight-element MIMO antenna systems. The polarization and pattern diversity with high isolation of a ring-shaped microstrip slot antenna (RMSA) fed by a microstrip line is presented in [25]. Orthogonal polarization was obtained and isolation was enhanced by symmetrically positioning the C-shaped coupled-fed and L-shaped monopole slot four-antenna arrays, as shown in [26]. Eight-port MIMO antennas were shown to benefit from improved port isolation and reduced correlation between using a square loop radiating strip with orthogonal polarization [27]. The antennas described in [8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27] are good at isolating signals, but they are too bulky and have too many moving parts. Dual band Branch Line Coupler (BLC) is designed using T-shaped stepped stub lines [28]. The isolation between Branch Line Coupler (BLC) is increased by using low pass and band pass filter circuits are designed [29]. A simple microstrip resonator is used to enhance isolation in microstrip patch antenna arrays in [30]. Therefore, it is crucial to have MIMO antennas that are easy to deploy, have improved isolation, and are small in size for use in 5G sub-6 GHz and WLAN applications.

This communication proposes a novel compact fractal loaded two- and eight-element MIMO with excellent diversity for 5G Sub-6 GHz and WLAN applications. The suggested 72 × 72 × 1.6 mm³ (0.792λ × 0.792λ × 0.0176λ) antenna is made on FR4 dielectric material with a loss tangent of 0.02 and a relative permittivity of 4.4. The presented structure includes fractal-loaded circular patch antenna elements and a partial ground with a protruding T-shaped stub. Four triangle shaped slots in the substrate, along with a T-shaped stub on the ground, are employed to achieve good isolation in the entire bands. The designed antenna works at the 5G sub-6 GHz bands such as N77 (3.3–4.2 GHz), N78 (3.3–3.8 GHz), and N79 (4.4–5.0 GHz) in addition with WLAN band (5.15–5.85 GHz). The antenna offers strong impedance matching (S11 ≤ −10 dB) and high isolation of more than 15 dB between the antenna ports in the operating bands. The results are validated using the theory of characteristic mode analysis approach, and the results show good agreement. Moreover, the antenna provides ECC of below 0.005, a TARC of less than −10 dB, a MEG of −3 dB, a diversity gain of 10 dB, a CCL of 0.05, a peak gain of above 2.5 dBi, a radiation efficiency of more than 95%, and stable boresight radiation patterns, making it well suited for 5G sub-6 GHz and WLAN services. Further sections provide a full description of the designed antenna.

2. Antenna Design and Analysis

The proposed work initially started with two-element MIMO antenna and then extended to eight-element MIMO antenna. Both the antennas are fabricated on FR4-epoxy substrate material. The antennas are designed and simulated using Ansoft HFSS EM simulator. The following subsections discuss in detail the design and simulation of the two-element and eight-element MIMO antennas.

2.1. Two-Element MIMO Antenna Design and Evolution

The design of the novel compact two-element MIMO antenna is depicted in Figure 1. The proposed antenna of size 24 × 36 mm² (L × W) comprises fractal loaded circular shaped radiators and a partial ground plan with T-shaped stub. The proposed antenna is fed by 50-ohm microstrip line feed with dimensions L_f × W_f. The desired bands sub-6GHz 5G and WLAN band (5.15–5.85 GHz) are obtained by fractal loading and slots on ground plan near the feed line. The dimensions of the proposed two-element MIMO antenna are listed in

Table 1. Design parameters of the two-element MIMO antenna.

Parameter	Value (mm)	Parameter	Value (mm)	Parameter	Value (mm)
L	24	W4	5	D	6
W	36	Wf	2.3	E	2
Lg	8	Lf	12.5	F	1
L1	3	D1	5.75	R1	5.8
L2	15.5	D2	23	R2	3.3
W1	5	A	5.5	R3	1
W2	9.5	B	3.5	h	1.6
W3	1	C	1.5	εr	4.4

. The simulated S-parameters of the proposed antenna are shown in Figure 2. It can be observed from Figure 2 that the antenna is operating at sub 6 GHz and WLAN bands with good impedance matching characteristics (S11 ≈ 62 dB) and high isolation (or low mutual coupling) greater than 15 dB.

The evolution of the two-element antenna is illustrated in Figure 3a–d. Antenna#1 is designed by two circular-shaped radiating elements of radius R₁ mm each and a partial ground of size L_g × W mm². Two slots are etched on the ground plane to achieve impedance matching in the working band. Then, a T-shaped stub (L₂ × W₃ and W₃ × W₄) is protruded to improve the isolation above 15 dB between the antenna ports. It is evident from Figure 3e that all antennas are resonating at 4.25 GHz with a frequency range of (3.3–6.0) GHz and S21 of more than 15 dB, but they differ in S11 values. Later, a rectangular slot of size A × D mm² is etched from each circular patch element of Antenna#1 to form Antenna#2 as given in Figure 3b. As a result, S11 is improved from −35 dB to −42 dB. Antenna#3 is constructed by adding R₂ mm radius circle with rectangular slot cut (B × E mm²) to the Antenna#2. The S11 is increased from −42 dB to −45 dB due to the inclusion of rectangular slotted circle. Finally, the proposed antenna denoted by Antenna#4 is formed by loading circle of radius R₃ mm with rectangular slot of C × F mm² to the Antenna#3 which results in further improvement in S11 from −45 dB to −62 dB. It is observed that Antenna#4 (proposed antenna) offers good impedance matching characteristics (S11 = −62 dB) and hence is adopted in this work. The S21 responses of all the evolution stages are depicted in Figure 4f.

2.2. Evolution Two-Element MIMO Antenna Parametric Analysis

The parametric analysis is conducted on two-element MIMO antenna design parameters (such as L_g, W_f, L₁, and W₃) to better understand its behavior in terms of impedance matching (S11) and isolation (S21) characteristics, as depicted in Figure 4. It is noticed from Figure 4a that the lower cutoff frequency is around 3.3 to 3.4 GHz and higher cutoff frequency is about 6 GHz for all values of ground plane length L_g. However, when compared with L_g = 7 mm and 9 mm, L_g = 8 mm provides better S11 values and hence is selected as ground plane length in the proposed design. The effect of the feed width (W_f) on the impedance matching characteristics is presented in Figure 4b. It is found that as W_f changes from 1.3 to 2.3 mm, the lower cutoff frequency is shifting to right and upper cutoff frequency shifts to the left. Additionally, the S11 value for W_f = 1.3 mm and W_f = 2.3 mm is relatively less when compared with W_f = 1.8 mm. The required frequency band from 3.3 to 6.0 GHz with good S11 value is obtained for feed width W_f = 1.8 mm and hence selected in this proposed design. To improve the impedance characteristics (S11), two slots are etched from the ground plane under the feed line. The slot width denoted by L₁ plays a crucial role in improving S11 as given in Figure 4c. It is identified that as L₁ changes from 2 to 4 mm, the S11 parameter also changes. The required band from 3.3 to 6.0 GHz with good S11 value is achieved for slot width L₁ of 3 mm and therefore chosen in this design.

Figure 4d represents the effect of T-shaped stub width W₃ on the S11 and S21 (isolation parameter). It can be observed that the impedance matching (S11) is improved from −25 dB to 62 dB, but port isolation (S₂₁) is decreased from 27 dB to 15 dB as the stub width W₃ decreases from 3 to 1 mm. W₃ = 3 mm offers high isolation, but poor impedance matching (S₁₁ = −25 dB). However, W₃ = 1 mm provides good impedance matching with acceptable port isolation and hence is selected in this design.

2.3. TCM Analysis

The results of the proposed two-element MIMO antenna are verified by performing theory of characteristic mode (TCM) analysis which is discussed in [31,32]. The parameters such as modal significance (MS) and characteristic angle $({\theta }^0)$ are analyzed as a function of frequency. From the modal significance (MS) plot, a mode is said to be resonant mode when its modal significance value is in between 0.7 and 1.0. The modal significance (MS) as a function of frequency is depicted in Figure 5a. It can be found that modes such as Mode 2–5 and Mode 7 are the resonant modes since their value MS value is more than 0.7 and Mode 1 and Mode 6 are the non-resonant modes below 6 GHz. The characteristic angle $({\theta }^0)$ vs. frequency plot is depicted in Figure 5b. A mode is said to be resonant mode when its ${\theta }^0$ value is around 180° as per the characteristic angle vs. frequency plot. It can be identified from Figure 5b that the Mode 2–5 and Mode 7 are the resonant modes as their ${\theta }^0$ values are around 180° and Mode 1 and Mode 6 are the non-resonant modes because their ${\theta }^0$ values are below 180°. The TCM analysis results agree well with the already proposed results. The equations of modal matrix, modal significance, and characteristic angle are represented in Equations (1)–(3) [33,34].

$$X\left(J_n\right)={\mathsf{\lambda }}_{n}R\left(J_n\right)$$

(1)

$$MS=\left|\frac{1}{1+j{\mathsf{\lambda }}_n}\right|$$

(2)

$${\alpha }_n={180}^{°}-ta{n}^{-1}\left({\mathsf{\lambda }}_n\right)$$

(3)

The 3-D polar radiation characteristics of the two-element MIMO antenna at 3.5 GHz, 4 GHz, 4.5 GHz, and 5.5 GHz are presented in Figure 6. The proposed antenna offers steady boresight radiation patterns in the z-direction at all abovementioned frequencies, which makes it ideal for WLAN and 5 G sub-6 GHz applications.

2.4. Eight-Element MIMO Antenna Design and Analysis

The design of eight-element MIMO antenna of size 72 × 72 mm² is depicted in Figure 7. The basic reason for extending two-element to eight-element is to enhance the capacity and data rate of the wireless devices. In the proposed design, all the two-element antennas are orthogonally spaced to enhance the isolation between the antenna ports. Furthermore, four triangle-shaped slots are etched at the center of the dielectric substrate to enhance the isolation above 15 dB. The impedance matching and isolation curves of the eight-element antenna are illustrated in Figure 8.

The S–parameters (S_ii, where i = 1 to 8) are drawn as two plots, namely S_ii (i = 1–4) and S_ii (i = 5–8), because the influence of adjacent elements on A1–A4 is different from that of A5-A8. Nevertheless, both plots satisfy the impedance matching requirements, as found from Figure 8. The S–parameter values such as S₁₁, S₂₂, S₃₃, and S₄₄ of the elements A1–A4 are the same and the S–parameters such as S₅₅, S₆₆, S₇₇, and S₈₈ of the elements A5–A8 are similar. However, the isolation parameters are different for different elements, as observed in Figure 8. The proposed eight-element MIMO antenna provides good impedance matching behavior with isolation of above 15 dB at all desired frequency bands.

2.5. Eight-Element MIMO Antenna Surface Current Distribution Analysis

The isolation parameter is also analyzed at resonant frequencies such as 3.5 GHz, 4 GHz, 4.5 GHz, and 5.5 GHz by using the surface current distribution when port-1 is excited, whereas other ports are terminated by 50-ohms load, as presented in Figure 9. As observed in Figure 9, without decoupling structure, the surface current of one element is entered into adjacent elements which degrade the radiation performance of the antenna. However, with T-shaped stubs and triangle-shaped slots, the surface currents are blocked and thus improve the isolation between the ports.

3. Results and Discussion

3.1. S-Parameters

The comparison of simulated and measured S-parameters (S_ii, where i = 1 to 8) are plotted in Figure 10. It is identified from Figure 10 that the antenna operates from 3.3 GHz to 6 GHz covering four bands such as N77 (3.3–4.2 GHz), N78 (3.3–3.8 GHz), N79 (4.4–5.0 GHz), and WLAN (5.15–5.85 GHz) with good impedance matching properties. The simulated and measured findings are in good agreement; however, there is a small difference because of conducting, dielectric, and SMA connection losses as well as fabrication tolerances. Figure 11 illustrates the measured isolation parameters of the proposed antenna. The proposed antenna offers enhanced isolation of greater than 15 dB between the antenna ports. Figure 8 and Figure 11 show that, with a few minor exceptions, there is a good match between the values for simulated and measured isolation. Figure 12 depicts the fabricated prototype of eight-element MIMO antenna.

3.2. Radiation Characteristics

One of the most crucial characteristics of any antenna is its radiation performance. It specifies the nature of the fields, their strength, and the direction in which they are emitted. Figure 13 represents the two and eight-element MIMO antenna radiation efficiency and peak gain response curves. The proposed design achieves more than 95% radiation efficiency and greater than 2.5 dBi in the entire working band from 3.3–6.0 GHz. The simulated and measured E- and H-field radiation patterns at 3.5 GHz, 4 GHz, 4.5 GHz, and 5.5 GHz working bands of the proposed element MIMO antenna are depicted in Figure 14. It is noticed that E-fields are bi-directional and H-fields are omnidirectional patterns. Additionally, it can be found from 3-D polar patterns that the antenna has steady boresight radiation patterns at resonant bands that make it ideal for WLAN and 5G sub-6 GHz communication.

3.3. MIMO Diversity Characteristics

The envelop correlation coefficient (ECC) is a parameter used to analyze the MIMO antenna diversity [15]. Equations (4) and (5) for an N- and two-element system represent the ECC, which specifies how the channels are correlated. ECC if 0 means no correlation and 1 means very high correlation between the signals. ECC of less than 0.5 is the allowable value of ECC in practical applications. Figure 15a,b describes the simulated and measured ECC curves of the proposed eight-element MIMO antenna. It can be found that the proposed structure offers <0.005 throughout the band.

$$EC{C}_{S-Parameters}=\frac{{\left|S_{ii}^{*}{S}_{ij}+S_{ji}^{*}{S}_{jj}\right|}^2}{\left(1-({\left|S_{ii}\right|}^2+{\left|S_{ij}\right|}^2)\right)\left(1-({\left|S_{jj}\right|}^2+{\left|S_{ij}\right|}^2)\right)}$$

(4)

$$EC{C}_{12}=\frac{{\left|S_{11}^{*}{S}_{12}+S_{21}^{*}{S}_{22}\right|}^2}{(1-{\left|S_{11}\right|}^2-{\left|S_{21}\right|}^2)(1-{\left|S_{22}\right|}^2-{\left|S_{12}\right|}^2)}$$

(5)

The diversity gain (DG) is a measure of the performance level of antenna diversity approaches [15,35]. Equation (6) can be used to evaluate the proposed MIMO antenna diversity performance. Figure 16 depicts the simulated and measured DG plots as a function of frequency where DG of approx. 10 dB is achieved across the working band.

$$DG=10\sqrt{1-{\left|EC{C}_{S-Parameters}\right|}^2}$$

(6)

Individual antenna S-parameter values are insufficient to analyze MIMO system performance when two or more antennas are placed next to each other. When both antenna elements are activated simultaneously, the radiation impacts the other antenna. Individual self-impedance and mutual impedance will vary. The S-parameters of individual MIMO antennas will not provide a perfect analysis. Total active reflection coefficient (TARC) is used to assess MIMO system behavior. TARC considers self and mutual impedance changes [36,37]. The following equation calculates the TARC for a two-port MIMO system (7). The proposed structure has TARC values below −10 dB across the spectrum Figure 17a,b.

$$TARC=\sqrt{\frac{\left|{\left(S_{11}+S_{12}{e}^{j\theta }\right)}^2\right|+\left|{\left(S_{21}+S_{22}{e}^{j\theta }\right)}^2\right|}{2}}$$

(7)

The channel capacity loss (CCL) defines how many bits are lost when two or more channels transmit signals at the same time. The mutual coupling between antenna elements is one of the main causes of capacity loss. Equations (8)–(10) are used to find the CCL in terms of S-parameters. The simulated and measured CCL plots are given in Figure 18. The proposed design delivers the CCL of <0.02 in the entire band.

$$C_{Loss}=-lo{g}_{2}det\left({\alpha }^R\right)$$

(8)

where ${\alpha }^R=\left[\begin{array}{cc}{\alpha }_{ii}& {\alpha }_{ij}\\ {\alpha }_{ji}& {\alpha }_{jj}\end{array}\right]$.

$${\alpha }_{ii}=1-\left({\left|S_{ii}\right|}^2+{\left|S_{ij}\right|}^2\right); {\alpha }_{ij}=-\left(S_{ii}{}^{*}{S}_{ij}+S_{ji}{}^{*}{S}_{jj}\right);$$

(9)

$${\alpha }_{ji}=-\left(S_{jj}{}^{*}{S}_{ji}+S_{ij}{}^{*}{S}_{ii}\right); {\alpha }_{ii}=1-\left({\left|S_{jj}\right|}^2+{\left|S_{ji}\right|}^2\right).$$

(10)

The mean effective gain (MEG) is a diversity performance indicating parameter that describes an antenna’s ability to receive electromagnetic signals in a multipath environment [38]. Equation (11) is used to calculate the MEG of the proposed antenna. Figure 19a,b illustrates the simulate and measured MEG plots, respectively. It is seen that the MEG of −3 dB is obtained in complete band from 3.3 to 6.0 GHz.

$$ME{G}_i=0.5{\eta }_{i,rad}=0.5\left[1-{\displaystyle \sum }_{j=1}^M{\left|S_{ij}\right|}^2\right]$$

(11)

Table 2. Performance comparison.

Ref.	No., of Elements	Size (in mm3)	Size (in Terms of λ)	Bands (GHz)	Isolation (dB)	Gain (dBi)	R.E (%)	ECC	DG (dB)	TARC (dB)	CCL (bits/sec/Hz)	MEG (dB)
[8]	2	46 × 30 × 1.6	0.276 × 0.18 × 0.0096	1.8–3.63, 5.07–7.96	17.21, 22.42	1.14–4.12, 1.42–4.78	>72	<0.003	10	−5	<0.35	<−3
[9]	2	150 × 75 × 0.8	1.7 × 0.85 × 0.009	3.4–3.6, 4.8–5.0	17.5, 20	-	>70	<0.14, <0.12	-	-	-	-
[10]	2	20 × 14.75	0.1586 × 0.1170	2.38–3.00, 3.21–3.61, 5.02–6.18	>15	7.93, 4.23, 7.57	-	<0.027	9.998	<−10	-	<−3
[11]	2	160 × 70 × 0.787	2.986 × 1.306 × 0.01469	5.6–5.67	>30	-	>85.1	<0.005	9.999	-	-	-
[12]	2	50 × 100 × 1.5	0.45 × 0.9 × 0.0135	2.7–3.6	>13	>3	>80	<0.009	-	-	-	<−3
[13]	2	23 × 19 × 0.406	0.253 × 0.209 × 0.004466	3.3–3.6, 4.8–5.0	>25	-	-	<0.3	-	-	-	-
[14]	2	16 × 26 × 0.8	0.144 × 0.234 × 0.0072	2.7–14.9	>20	0.8–6.6	≥86	<0.06	9.975	≤−10	-	-
[15]	2	16 × 26 × 1.6	0.1504 × 0.2444 × 0.01504	2.82–14.45	>22	6.86	>91	<0.08	9.984	<−10	-	-
[16]	2	2.61λ × 1.49λ	2.61 × 1.49	26.7–29.2	>34.76	7.81	86	-	-	-	-	-
[17]	2	22 × 26 × 0.8	0.2273 × 0.2686 × 0.00826	3.1–11.8	>20	3.6–6	>85	<0.03	-	-	-	-
[18]	2	18 × 21 × 0.8	0.168 × 0.196 × 0.00746	2.8–12.2	>25	2–5	>80	<0.013	-	-	-	-
[19]	4	50 × 50 × 1.6	0.566 × 0.566 × 0.01813	3.4–3.8	>12	>3.6	-	<0.08	-	-	-	-
[20]	4	Size not mentioned clearly	-	3.4–3.8	>20	5	>80	<0.004			<0.2
[21]	4	75 × 150 × 1.6	0.825 × 1.65 × 0.0176	3.3–7.1	>12	4.6–6.2	>48	<0.07	-	<−10	<0.4	-
[22]	4	30 × 40 × 16	0.32 × 0.4266 × 0.1706	3.2–5.85	>17.5	3.5	85	<0.05	9.98	<−10	<0.4	<−6
[23]	4	75 × 150 × 1.6	0.825 × 1.65 × 0.0176	3.3–3.9	18	3	>60	<0.001	-	<−10	<0.4	-
[24]	4	30 × 30 × 0.8	0.34 × 0.34 × 0.00906	3.4–6.3	>15	4	96	<0.001	-	-	<0.4	-
[25]	8	80 × 150 × 0.8	0.96 × 1.8 × 0.0096	3.6–3.8, 5.15–5.92	>15	>3	>54	<0.05	-	<−6	-	-
[26]	8	68 × 136 × 1	0.578 × 1.156 × 0.0085	2.55–2.65	>12.5	3	>53	<0.15	-	-	-	<−5
[27]	8	68 × 136 × 6	0.578×1.156×0.051	2.55–2.65	>13	2.2–3	>48	<0.1	-	-	-	<−5
Pro.	8	72 × 72 × 1.6	0.792 × 0.792 × 0.0176	3.3–6.0	>15	>2.5	>95	<0.005	9.99	<−10	<0.05	<−3

shows the performance evaluation of the proposed MIMO antenna compared to others that have been described earlier. It is found that the proposed design offers better performance with respect to the impedance bandwidth, isolation, peak gain, ECC, DG, TARC, CCL, and MEG when compared with the existing antennas. Additionally, the size of the proposed eight-element antenna is small compared to existing eight-element antennas.

4. Conclusions

This communication proposes a novel compact fractal loaded two- and eight-element MIMO with high diversity for 5G Sub 6 GHz and WLAN applications. The presented antenna comprises fractal loaded circular patch elements and a partial ground with protruded T-shaped stub. Four triangle shaped slots in the substrate, along with a T-shaped stub on the ground, are employed to achieve good isolation in the complete band. The proposed antenna works at (3.3–6.0) GHz, covering the 5G sub-6GHz bands N77, N78, N79, and WLAN, with good impedance matching and high isolation characteristics. The antenna results are validated using the TCM analysis, and there is good agreement between the results. The antenna has a peak gain of >2.5 dBi, a radiation efficiency of above 95%, and steady boresight radiation patterns, making it well suited for 5G sub-6 GHz and WLAN communication.