# Design of a Modified MIMO Antenna Based on Tweaked Spherical Fractal Geometry for 5G New Radio (NR) Band N258 (24.25–27.25 GHz) Applications

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## Abstract

**:**

## 1. Introduction

## 2. Antenna Design

^{3}and has a simple construction. An economical FR4 substrate material is used to manufacture the antenna. The subsequent parts will cover the stepwise design process, optimization, and the accompanying results.

#### 2.1. Single Antenna Design Evolution Steps

_{o}is the free space speed of light; ε

_{r}is the dielectric constant of material.

#### 2.2. Two-Element MIMO Antenna Design

^{2}substrate dimensions. In order to create a dual-port MIMO antenna, two separate investigations are undertaken with the objective of attaining optimal outcomes. Initially, the focus of the study is on optimizing the spacing between two antenna elements. Subsequently, the antenna is examined in three distinct orientations, labeled as I, II, and III.

#### 2.2.1. Distance Optimization

#### 2.2.2. Analysis of Orientation

#### 2.2.3. Analysis of MIMO Antenna with Defective Ground Structure

## 3. Results and Discussion

#### 3.1. Analysis of Diversity Performance

#### 3.1.1. Envelope Correlation Coefficient

#### 3.1.2. Diversity Gain

#### 3.1.3. Mean Effective Gain

## 4. Comparison with Prior Research Works

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Design process. (

**a**) Conventional spherical patch antenna; (

**b**) fractal spherical patch antenna; (

**c**) MIMO antenna; (

**d**) MIMO antenna with DGS.

**Figure 12.**Distribution of surface current by exciting port 1 and discontinuing port 2 at (

**a**) 9.7 GHz (

**b**) 18.8 GHz, and (

**c**) 21.4 GHz.

**Figure 14.**Experimental setup. (

**a**) Measurement of reflection coefficient S11 dB; (

**b**) measurement of radiation pattern.

**Figure 16.**Radiation pattern simulation and measurement: (

**a**) (E plane) 9.5 GHz, (

**b**) (H Plane) 9.5 GHz, (

**c**) (E plane) 21.1 GHz, (

**d**) (H Plane) 21.1 GHz, (

**e**) (E plane) 26.6 GHz, (

**f**) (H Plane) 26.6 GHz.

Radius A1 | Radius A2 | Radius A3 |
---|---|---|

N1 = Number of circles = 5^1 | N2 = Number of circles = 5^2 | N3 = Number of circles = 5^3 |

L1 = Scaling factor L1 = (1/3)^1 = 0.333 | L2 = Scaling factor L2 = (1/3)^2 = 0.111 | L3 = Scaling factor L3 = (1/3)^3 = 0.037 |

A1 = 0.333 × 9.31 = 3.10 mm | A2 = 0.111 × 9.31 = 1.03 mm | A3 = 0.037 × 9.31 = 0.344 mm |

Parameters | Values | Parameters | Values |
---|---|---|---|

L_{S} | 28.22 mm | F_{L} | 11.007 mm |

W_{S} | 28.22 mm | F_{W} | 2.99 mm |

A | 9.31 mm |

Parameters | Bandwidth (MHz) | f_{r} (GHz) | S11 (dB) |
---|---|---|---|

0th iteration | 400, 5400, 3800 | 9, 18.8, 26.4 | −19.6, −24.2, −23.5 |

1st iteration | 1200, 5200, 3800 | 9.3, 21.7, 26.2 | −23.8, −26.2, −23.4 |

2nd iteration | 1000, 700, 5500, 3700 | 9.2, 10.6, 18.8, 26.6 | −24.7, −12.1, −24.5, −23.7 |

3rd iteration | 1000, 700, 200, 5500, 3800 | 9.2, 10.6, 16.3, 21.5, 26.7 | −26.8, −12.4, −10.8, −28.6, −25.5 |

Parameters | Bandwidth (MHz) | f_{r} (GHz) | S12 (dB) (Max. Isolation) |
---|---|---|---|

D = 2 mm | 3100, 400, 10,000 | 9.2, 16.3, 18.9, 21.3 | −38.9 |

D = 4 mm | 3100, 600, 10,100 | 9.7, 16.3, 18.8, 21.4 | −40 |

D = 6 mm | 2800, 600, 9900 | 9.1, 16.5, 18.9, 21 | −38.6 |

Parameters | Bandwidth (MHz) | f_{r} (GHz) | S12 (dB) (Max. Isolation) |
---|---|---|---|

Orientation I | 3100, 600, 10,100 | 9.7, 16.3, 18.8, 21.4 | −40 |

Orientation II | 3000, 600, 9900 | 10.3, 16.4, 18.8, 21.5 | −38.74 |

Orientation III | 2700, 9800 | 8.2, 19.2 | −37.21 |

Parameters | Bandwidth (MHz) | f_{r} (GHz) | S12 (dB) (Max. Isolation) |
---|---|---|---|

MIMO | 3100, 600, 10,100 | 9.7, 16.3, 18.8, 21.4 | −40 |

MIMO DGS | 2200, 400, 9900 | 9.7, 16.3, 18.8, 21.4 | −52.72 |

Parameters | Value |
---|---|

ECC | <0.004 |

Diversity gain | >9.99 dB |

Mean effective gain | <1.2 dB |

Ref | Bandwidth (MHz) | No. of Port | No. of Band | Element Spacing (mm) | Isolation | ECC | Diversity Gain | Range |
---|---|---|---|---|---|---|---|---|

[9] | 400, 400, 11,000 | 2 | 3 | - | −32.3, −35.4, −27.23, −28.44 | <0.05 | ---- | Sub 6 GHz and mm Range (5G) |

[13] | 1069, 1430 | 2 | 2 | 10.13 | −27 | <0.0020 | ---- | mm Range (5G) |

[15] | 6400 | 2 | 1 | - | −35.8 | <0.005 | >9.99 | mm Range (5G) |

[16] | 7900 | 2 | 1 | - | <−18 | <0.01 | >9.96 | C Band and X Band |

[17] | 1900, 5500 | 2 | 2 | 4.3 | <−34, <−22.2 | <0.0001, <0.0002 | >9.99 | mm Range (5G) |

[18] | 8700 | 2 | 1 | - | < −30 | <0.05 | >9.99 | mm Range (5G) |

[21] | 500, 1800, 800, 1000 | 4 | 4 | 10 | ---- | <0.06 | >9.99 | mm Range (5G) |

[22] | 1000 | 2 | 1 | 6 | <−25 | <0.002 | ---- | mm Range (5G) |

[25] | 821, 1630 | 2 | 2 | 8.8 | <−16 | 0.0002, 0.005 | >9.98 | Sub 6 GHz and mm Range (5G) |

[26] | 6000 | 2 | 1 | 3 | <−24 | <0.0013 | >9.99 | mm Range (5G) |

[28] | 200, 600, 1000 | 2 | 3 | 3.3 | >15 | <0.04 | >9.5 | Sub 6 GHz (5G) |

[29] | 1000, 500, 800 | 4 | 3 | 3.85 | <−20 | <0.01 | 10 | Sub 6 GHz (5G) |

Proposed | 1000, 1000, 600, 800, 10,300 | 2 | 5 | 4 | −31.4,−22.8, −26.8, −22, −24.4 | <0.004 | >9.99 | X, Ku Band and mm Range (5G) |

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**MDPI and ACS Style**

Bisht, N.; Malik, P.K.; Das, S.; Islam, T.; Asha, S.; Alathbah, M.
Design of a Modified MIMO Antenna Based on Tweaked Spherical Fractal Geometry for 5G New Radio (NR) Band N258 (24.25–27.25 GHz) Applications. *Fractal Fract.* **2023**, *7*, 718.
https://doi.org/10.3390/fractalfract7100718

**AMA Style**

Bisht N, Malik PK, Das S, Islam T, Asha S, Alathbah M.
Design of a Modified MIMO Antenna Based on Tweaked Spherical Fractal Geometry for 5G New Radio (NR) Band N258 (24.25–27.25 GHz) Applications. *Fractal and Fractional*. 2023; 7(10):718.
https://doi.org/10.3390/fractalfract7100718

**Chicago/Turabian Style**

Bisht, Nitasha, Praveen Kumar Malik, Sudipta Das, Tanvir Islam, Sivaji Asha, and Moath Alathbah.
2023. "Design of a Modified MIMO Antenna Based on Tweaked Spherical Fractal Geometry for 5G New Radio (NR) Band N258 (24.25–27.25 GHz) Applications" *Fractal and Fractional* 7, no. 10: 718.
https://doi.org/10.3390/fractalfract7100718