Analysis and Design of Sub-6 Beam Steerable Antenna Array Using Meta-material Loaded Vivaldi Elements.

doi:10.21203/rs.3.rs-1756851/v1

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Analysis and Design of Sub-6 Beam Steerable Antenna Array Using Meta-material Loaded Vivaldi Elements.

https://doi.org/10.21203/rs.3.rs-1756851/v1

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published 21 Mar, 2023

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in this paper, a sub-6 beam-steerable antenna array system is introduced. The main radiating element in the proposed array is a gain-enhanced Vivaldi antenna, whose overall realized gain is improved by introducing near-zero-index metamaterial [NZIM] with broadband characteristics at 3.6 GHz. The proposed system is intended to be integrated with fifth-generation (5G) automotive applications. The 4x4 butler matrix is resonating at 3.6 GHz to feed the designed antenna array elements and steer the radiating beam, which is suitable for automotive applications. All the system components, including antenna elements and the [4x4] butler matrix, are designed, simulated, and optimized by using CSTMWS 2020 and HFSS. In order to verify the proposed design, the system is fabricated using the photolithographic technique. The experimental results show very good agreement with the simulated ones. The NZIM-loaded antenna element achieves a -10 dB bandwidth of 2.9 GHz, while the overall array system achieves a 600 MHz bandwidth. The steered beam of the proposed system has an overall realized gain of 11.2 dB and covers an angle from 45^o to 135^o.

Automotive antenna

Vivaldi antenna

Butler matrix

meta-material

Beam-steering.

Over recent years, automotive technology has been rapidly changing, which requires a significant increase in the data rate transferred. Development in the wireless network industry is becoming very necessary to meet the huge demand for such data rates. Many countries have adopted the fourth generation (4G) wireless communication system. However, some drawbacks, including overcrowded spectrum, high energy consumption, and high data rates, are not solved by 4G [1]. In comparison to the previous generation of 4G, 5G introduces significant differences and promises more benefits, such as wider bandwidth and less congested spectrum. The main goal of 5G technology is to improve the data rate by 1000 times compared to common communication standards and to connect 100 billion devices. The high data rates of several Gbps need even more support from the use of higher frequency bands, so 5G needs a wide spectrum across low, mid ,and high ranges to deliver widespread coverage and support all use cases. AutomotiveWireless communications include various applications, including automated driving of vehicles, driver assistance systems, vehicle-to-everything (V2X), vehicle-to-vehicle (V2V), and vehicle-to-infrastructure (V2I) [2]. The automotive applications need antennas that have some properties like beam steerable, wide bandwidth, and high realized gain. However, the automotive applications are loaded with optional antennas, so the proposed system is loaded with an antenna that has beam-steering, high gain, and wide bandwidth properties to work in different environmental conditions to cover important automotive services and support a high data transfer rate [3]. Antenna-array systems with butler-matrix are one of the methods to achieve the desired aims. In this paper, the single-element antenna is a Vivaldi, which was suggested by Gibson [4]. The single element is loaded with NZIM to improve the overall realized gain [5]. Beam steering is a technique to steer the beam by controlling the phase of each element. The [4x4] butler matrix is optimized for this aim [6, 7].

A single Vivaldi element is designed and optimized to operate at 3.6 GHz with broadband characteristics. The Vivaldi antenna meets the desired purpose [8]. Roger RT5880 with relative permittivity (ε_r = 2.2), a thickness of .787mm, and low tangent losses (tan δ = .0009) is chosen for sub-6 antennas to reduce losses, especially in antennas that operate at high frequencies. The single element geometry is shown in Fig. 1. The proposed design dimensions are presented in Table 1. Also, the simulated return loss S₁₁ is shown in Fig. 2. CSTMWS 2020 and HFSS, two software packages that differ in their simulation techniques, were used to simulate the proposed designed system [9].

Table 1

The Optimized Dimensions of Proposed Vivaldi Antenna.
parameter	ws	Lt	Lp	Ln	Lc	S	Wq	D	Rs	Rw	Sd	r	α
Value (mm)	86	80.30	68.80	8.60	39.11	12.58	1.20	4.80	2.45	2.64	1.20	15	90^o

The results simulated by the two programs are close to the measured results, achieving a -10 dB bandwidth of 2.9 GHz for a single Vivaldi element.

The phase velocity of propagating electromagnetic waves tends to infinity in the NZIM metamaterials. As a result, the final wavelength also tends to infinity. The NZIM metamaterial is used as a high refractive index impact to result in a confined pattern and high directivity [10]. Also, by providing a high-refractive-index effect, the metamaterial is intended to replace dielectric lenses for gain enhancement [10]. So, the NZIM units use the same thickness of dielectric material to be introduced within the front of a Vivaldi antenna [11, 12]. The NZIM metamaterial is used in essential applications such as producing unwanted impedance mismatch in the desired system [13]. The unit cell dimension is optimized and simulated using CSTMWS 2020. The NZIM unit cell dimensions are (Ls = 7mm, Lm = 6mm, and Wx = 0.5mm) as shown in Fig. 3.

The value of the n index is approximately near zero, its real value is 0.1885, and the image value is zero. The designed element of the Vivaldi antenna aperture is filled with NZIM to improve the overall realized gain, as shown in Fig. 4.

It was required to analyze the impact of the NZIM units on the realized gain after they were added to the proposed single element. Hence, the realized gain versus frequency is simulated using CSTMWS 2020 in Fig. 5.

The value of the maximum overall realized gain is 8.6418 dB at a frequency of 3.6 GHz when three columns of the NZIM unit cells are added to a single Vivaldi element. The NZIM unit cells achieve a confined pattern with high directivity and increase the overall realized gain by 1.12 dB.

Beam-steering is one of the important properties in automotive communications. The proposed system is fed by a Butler matrix, which is considered a passive beam-steering network. The Butler matrix was proposed by Butler and Lowe in 1961. It consists of a 90° hybrid Coupler, crossover, and phase shifter[14].

4.1. 90° Hybrid Coupler

A hybrid coupler is a passive four-port network, as shown in Fig. 6, that splits the input power into two equal-power signals at the outputs, and the fourth port is isolated. The coupling is 3 dB and half-power split at the outputs. For a 90° hybrid coupler, the outputs differ in phase by 90° [6, 14].

The 3-dB coupler is designed in HFSS and CSTMWS 2020 to obtain the S-parameters, and phase difference between coupled ports as shown in Fig. 7.

4.2. Crossover

The crossover is optimized with a high level of isolation between the input ports to avoid overlapping signals during crossings. It is simple to construct by cascading two-hybrid 3-dB couplers [15]. The designed crossover and simulated results with good isolation between ports are shown in Fig. 8.

4.3. Phase shifter

In the designed system, phase shifters are critical components. The power at the output of the micro-stripline phase shifter should be identical to the input power, implying a 0 dB insertion loss. However, there are dielectric and conductor losses that degrade the insertion loss owing to the non-ideal transmission line length [16]. At higher frequencies, these losses are more pronounced. The phase difference between the input and output ports can be easily changed by changing the electrical length of the line [7].

4.4. The [4x4] Butler matrix

The butler matrix is designed, optimized, and fabricated. The simulation results are obtained using CSTMWS 2020 and HFSS. The output ports are separated by (𝝺o/2), which is equal to approximately 42 mm at an operating frequency of 3.6 GHz to avoid mutual coupling between array elements. The proposed design layout is shown in Fig. 9.

The results for the [4x4] butler matrix phase difference between output ports simulated by using CSTMWS 2020 and HFSS are shown in Fig. 10.

In this section, the complete designed system results are obtained by using the Advanced Design System (ADS 2019) simulator to show mutual coupling between input ports and return loss for input ports [17]. The results were presented in Fig. 12 and compared with the measured ones. The data is extracted from CSTMWS 2020 (Touchstone files) and is used to obtain results in ADS 2019 as shown in Fig. 11.

The results obtained by ADS 2019 are approximately as measured. To achieve beam steering, the phase of the input signal is adjusted for all radiating components [18, 19].As shown in Table 2, the Butler matrix achieves this goal. Also, Fig. 13 shows beam steering simulated results by using CSTMWS 2020 compared to measured results.

Table 2

The phase difference between ports by using CSTMWS 2020 at an operating frequency of 3.6 GHz.
cases :	case 1	case 2	case 3	case 4
port Excitation	port (p1)	port (p2)	port (p3)	port (p4)
port (p5)	-108.239	-6.401	-60.390	30.313
port (p6)	-66.042	-154.906	65.874	-20.218
port (p7)	-20.218	65.874	-154.906	-66.042
port (p8)	30.313	-60.390	-6.400	-108.239

At the operating frequency of 3.6 GHz, the maximum measured realized gain is 11.2 dB, and the butler matrix enabled the system to cover an angle from 45^o to 135^o, which steered the beam in the desired direction as shown in Fig. 13. Also, the proposed system achieves a -10 dB bandwidth of 600 MHz as shown in Fig. 12. The high gain, wide bandwidth, and beam steering technology in the designed system make communications possible in remote locations and critical environmental conditions for automotive applications. Beam steering in automotive applications helps to reduce multipath fading occurrences by forming the beam in the desired direction to avoid interference and noise sources. In addition, steerable antennas enable sensors to achieve longer ranges, higher data rates, and lower power consumption (longer battery life) [20, 21].

In this paper, the proposed design is simulated and fabricated, showing good results. The proposed single Vivaldi element supports the entire sub-6 GHz frequency bands and is loaded by the NZIM units to increase overall realized gain. The passive beam steering network is a butler matrix, which is optimized at an operating frequency of 3.6 GHz with good isolation between ports and covers an angle from 45^o to 135^o. The proposed system has some properties that support automotive applications, such as high gain, wide broadband, and the property of beam steering. Automotive applications are becoming increasingly important in our life, and include very essential services such as v2x, v2v, and global positioning system (GPS), so the proposed system can be considered as a good candidate for this purpose.

Acknowledgments: The authors would like to thank Prof. Dr. Fawzy Ibrahim, Dean of the Egyptian Academy for Engineering and Advanced Technology, as well as the Ministry of State for Military Production for making available the measurements of fabricated circuits.

Author Contribution: All authors contributed to the study's conception and design. Abdel-Hamid Shaalan developed the final vision for the study as well as reviewed the work. Circuit preparation, data collection, and analysis performed by Ahmed Khairy. The first draft of the manuscript was written by Ahmed Khairy, Ayman Elboushi, and Mai Ahmed. All authors commented on previous versions of the manuscript.

Funding: No funding from an individual or organization.

Declarations: Availability of data and material upon request.

Conflict of Interest: The authors declare that they have no conflict of interest.

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No competing interests reported.

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Journal Publication

published 21 Mar, 2023

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Editorial decision: Major revision
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Reviewers agreed at journal
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You are reading this latest preprint version

Analysis and Design of Sub-6 Beam Steerable Antenna Array Using Meta-material Loaded Vivaldi Elements.

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Single Element Design

3. Near-zero-index Metamaterial [nzim]

4. Butler Matrix Components Design.

4.1. 90° Hybrid Coupler

4.2. Crossover

4.3. Phase shifter

4.4. The [4x4] Butler matrix

5. System Design And Result For Discussion.

6. Conclusion

Declarations

References

Additional Declarations

Status:

Journal Publication

Version 1