Slot-Notch Mechanism Enabled Circularly Polarized High Gain Antenna for 5G mm-Wave RF Energy Harvesting

doi:10.21203/rs.3.rs-4645295/v1

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Slot-Notch Mechanism Enabled Circularly Polarized High Gain Antenna for 5G mm-Wave RF Energy Harvesting

https://doi.org/10.21203/rs.3.rs-4645295/v1

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This article describes the design of a slot-notch mechanism-enabled broadband and high-gain microstrip antenna fed by a microstrip line for fifth-generation (5G) millimeter-wave applications. The antenna is designed using Rogers 4003 substrate having a relative permittivity of 3.38, thickness of 0.8 mm, and fed by a 50 Ω microstrip line. The suggested design comprises a rectangular patch with a rectangular slot at the center. Further, two open-ended rectangular notches at the upper edges and two rectangular-shaped stubs at the lower edges are included to achieve the desired requirements. The antenna is resonant at 32.6 GHz, exhibiting |S₁₁| around − 24.8 dB over a bandwidth of 1.5 GHz (31.7–33.2 GHz) and offering a maximum gain of 7.2 dBi. Circularly polarized radiation is achieved at 32.6 GHz with a 3-dB axial ratio bandwidth of 0.5 GHz (32.4–32.9 GHz). The antenna is fabricated and its simulated results are validated experimentally. Subsequent comparative analysis revealed that the proposed antenna is almost 60% more compact than similar designs reported in the literature.

Broadband

Circular Polarization

Energy harvesting

High gain

Millimeter-wave

The emergence of 5G technology has attracted substantial interest in modern wireless communication systems, mainly because of its wide-ranging applications across various fields. A notable application is the utilization of millimeter-wave (mm-wave) frequency spectra, especially those exceeding 20 GHz. However, the 5G spectrum has been allocated and categorized into the Sub-6-GHz band (< 6 GHz) and mm-wave bands. However, in the sub-6-GHz band, there is a shortage of available spectrum, prompting the adoption of mm-wave bands that satisfy the growing demand for higher data rates and enhanced reliability [1], [2]. The frequency spectrum designated for the mm-wave band ranges from 30 GHz to -300 GHz, but only the spectrum between 24 GHz and − 100 GHz is utilized currently [3]. This technology boasts numerous advantages, including expanded bandwidth, enhanced resolution, and minimal interference, and so it is well-suited for satellite communications, radar systems, virtual reality, routers etc. [4]. Despite the advantages, mm-wave communications still possess some drawbacks. One such limitation is the high atmospheric attenuation and associated loss in signal transmission. Therefore, mm-wave antennas require high-gain and a stable radiation pattern [5]. According to the World Radio Communication Conference (WRC-15), the usable mm-wave spectrum is classified into specific frequency bands, which include 24.25–28.35 GHz, 31.8–33.4 GHz, 37-43.5 GHz, 45.5–52.6 GHz, 66–76 GHz, and 81–86 GHz [6]. These frequency bands offer wider bandwidth and higher data rates, thus making them suitable for highly efficient designs [7]. Because of substantial power absorption in air, propagation, the electromagnetic spectrum between 20–60 GHz presents a problem for deployment [8], [9]. Significant advancements have been made in the past two decades with near-field coupling being the dominant approach while far-field wireless power transfer (WPT) has been employed for for replacing batteries.

Wireless energy harvesting (WEH) is similar to WPT but focuses on converting electromagnetic energy from the environment to power low-power IoT devices, reducing the need for batteries. Unlike WPT, WEH operates at much lower power levels and potentially across a wide frequency band. However, the power harvested is typically less than 1 µW, which may be insufficient for most practical applications [10], [11]. Thus, mm-wave antennas are needed to capture the corresponding electromagnetic spectrum for power transferring and energy harvesting applications, directly impacting harvesting efficiency. Also, wideband mm-wave antennas are essential to harvest energy from designated frequency spectrums [12].

In recent years, researchers have been increasingly exploring the potential of the mm-wave frequency spectrum in various wireless applications, including 5G communication systems [13]. Work in 5G applications demonstrates the utilization of different antenna types for constructing wireless communication systems [14], [15]. These include monopole [16], dipole [17], loop [18], antipodal Vivaldi [19], fractal [20], planar inverted F antennas [21], and others. Among these, the microstrip patch antenna (MPA) stands out as a promising candidate due to its special features, including a low profile, lightweight, low cost, and compatibility with MMIC (monolithic microwave integrated circuit), commonly utilized in mobile communication systems [22]. In [23], Radio Frequency Energy Harvesting (RFEH) technique is explored to reduce the dependency on conventional batteries. The RFEH method has been investigated extensively in spite of the fact that the surrounding environment has low power density available [24]. Single-band antenna designs are currently used because of their compact size and easy fabrication. Several planar antenna layouts, including broadband and multiband, have been used in [25], [26]. A thorough analysis of using high-gain antennas in energy harvesting systems was demonstrated in [27]. A series-coupled patch array [28] and an antipodal Vivaldi-based antenna [29] were also employed to realize high-gain. However, these techniques were especially susceptible to polarization mismatch. A series feeding structure incorporating a microstrip feeding line addressed this issue [30]. The antenna design demonstrated in [31]-[37] was intended for 5G applications and RF energy harvesting/wireless power transfer (RFEH/WPT) in the mm-wave spectrums. A dipole antenna array was designed to operate within a broad spectrum of 26.5–38.2 GHz and it achieved a gain of 4.5–5.8 dBi for 5G mobile applications [31]. Likewise, a CPW-fed circular slot antenna is designed in [32] for 5G smartphone applications. The reported antenna yielded an operational bandwidth of 5.5 GHz (26.5–32 GHz) and a forward gain of 8–9 dBi. Wagih et al. [33] proposed a textile-based on-body mm-wave antenna system operating at 26 GHz and 28 GHz with a gain of 7 dBi for RF energy harvesting. A novel mm-wave antenna system configuration for smartphone applications was reported in [34], exhibiting a wide frequency band of 24–28 GHz. An array of 16 such elements to exhibited beam steering capabilities with low side lobe levels. In [35], a novel approach to designing a self-complementary Bowtie antenna was presented for wireless power transfer applications. The design offered a compact size with a wide operational bandwidth of 25.8–40.1 GHz and a gain of 10.4 dBi. A highly flexible compact mm-wave antenna system for 5G wireless applications was proposed by Shariff et al. [36], utilizing a circular radiator with a T-shaped stub that operated over a wide bandwidth of 3.2 GHz, demonstrating outstanding performance. Authors in [37] presented a flexible, inkjet-printed mm-wave rectenna system. The design comprised an antenna array integrated with a rectifier operating at 24 GHz and a realized gain of 5 dBi. Generally acceptable performance was achieved in terms of compactness, operational bandwidth, and gain for 5G mobile communications and RF energy harvesting/wireless power transfer in the mm-wave spectra, [31]-[37]. Nevertheless, most of the designed antennas were bulky and had shortcomings in achieving satisfactory levels of symmetric radiation patterns. In addition, no significant attention was paid to address the mm-wave antenna designs for RFEH/WPT. Therefore, in the present work, a single-band microstrip antenna comprising a rectangular patch with the slots-notched mechanism on the radiating surface is employed to improve impedance matching, gain, and bandwidth at the desired frequency. The proposed work can offer a broad working bandwidth of 1.5 GHz (31.7–33.2 GHz), exhibiting a reflection coefficient of -24.8 dB. The recommended antenna structure provides a maximum gain of 7.2 dB, with circularly polarized radiation at 32.6 GHz with an axial ratio bandwidth of 0.5 GHz (32.4–32.9 GHz). The paper is structured into four sections. Section 1 presents the introduction. In Section 2, the geometrical design and simulated performance characteristics have been discussed. Section 3 outlines the experimental validation. Finally, Section 4 provides the conclusion.

The proposed antenna configuration is presented in Fig. 1. The top view in Fig. 1(a) incorporates a rectangular radiating patch with a central rectangular slot, two open-ended notches from the upper edge, and two short stubs at the lower edge to achieve the desired frequency band of interest. Figure 1(b) shows the ground plane layer backing the patch and the microstrip line. The antenna exhibits an overall size of 12.4×6×0.8 mm³ and it has a Rogers 4003 substrate having a relative permittivity of 3.38. The other optimized dimensions (in mm) are W = 6, L = 12.4, W₁ = 3.8, L₂ = 8.2, W₂ = 0.5. L₃ = 2, W₃ = 0.57, W₄ = 0.77, L₇ = 1, and W_f = 1. Figure 2 illustrates the evolution progression of the proposed antenna structure. A reference rectangular microstrip patch antenna is designed at the outset, denoted as Design-0, as illustrated in Fig. 2(a). This antenna resonates at 33.3 GHz with poor impedance matching, as shown in Fig. 3(a). The key objective of our design is to achieve a wide operational bandwidth within the mm-wave spectrum. Therefore, Design-0 is modified by inserting rectangular slots at the center of the radiating patch (Design-1). Design-1 shifts the resonant frequency towards 33.02 GHz with |S₁₁| = -12.6 dB. To verify the performance of Design-1, a parametric analysis corresponding to the design parameters L₂ and W₂ is demonstrated in Figs. 4(a) and 4(b). It seems that altering the values of L₂ and W₂ does not yield a notable impact on the resonance. Consequently, the optimized parameters are set at L2 = 8.2 mm and W2 = 0.5 mm. The gain of Design-1 is observed to be 5.1 dBi. However, Design-1 achieves no resonance with acceptable impedance matching. However, the desired requirements have not yet been fully met. Therefore, to achieve the required resonant frequency with wide impedance bandwidth and enhanced gain, Design-1 is further modified by introducing two open-ended rectangular notches, resulting in Design-2. Design-2 provides a resonance at 32.8 GHz with |S₁₁| = -12.5 dB. Nevertheless, Design-2 fails to improve the bandwidth but enhances the gain up to 6.6 dBi. In both Design-1 and Design-2, the resonant frequency shifted lower, as desired, but the impedance match is not acceptable. The resonant frequency is lowered due to the introduction of effective shunt inductance because of slot and open-ended notches that forced surface current to flow through a longer path, as marked with the arrow in the surface current distribution in Fig. 6. A parametric study of values of length L₃, and width W₃ of Design-2, illustrated in Figs. 4(c) and 4(d) show that as L3 and W3 increase, the antenna impedance matching simultaneously improves. The maximum values of L₃ and W₃ are observed to be 2 and 0.57 mm, respectively.

In Design-3 two asymmetric rectangular stubs at the lower edges of the patch are introduced, as illustrated in Fig. 2(d). This leads the antenna structure to resonate within the desired frequency band of 32.6 GHz with an operational bandwidth ranging from 31.7–33.2 GHz with a maximum gain of 7.2 dBi for 5G mm-wave applications. A parametric analysis of design parameters L7 and W4 (width and length of the rectangular notches) is performed. Figure 5 shows that increasing L7 and W4 shifts the antenna's resonant frequency higher. In the final design configuration, the antenna resonates at the desired frequency when L7 = 1 mm and W4 = 0.77 mm. In this case the antenna exhibits circularly polarized radiation at 32.6 GHz with an axial ratio bandwidth (ARBW) of 0.5 GHz (32.4–32.9 GHz). Figures. 3(a) to 3(c) show the simulated S11, gain, and axial ratio for the designed antennas (Design-1 to Design-3) summarized in Table 1 for comparison.

Table 1

Performance evaluation of different design steps
Design Steps	Geometry	f (GHz)	\|S₁₁\| (dB)	BW (GHz)	G (dBi)	AR-BW (dB)
D-0	Rec. Patch	33.3	-10.03	33.1–33.4	-1.04	NA
D-1	D-0 + Slot	33.02	-12.6	33.6–33.2	5.1	NA
D-2	D-1 + 2 notches	32.8	-12.5	32.4–33.0	6.6	32.7–32.9
D-3	D-2 + 2 stubs	32.6	-24.8	31.7–33.2	7.2	32.4–32.9

D-i: Design-i, i = 0, 1, 2, 3, f: Resonant frequency, BW: Bandwidth, G: Gain, AR-BW: Axial Ratio Bandwidth, NA: Not Available

This section explores the effectiveness of the proposed antenna design, supported by experimental measurements. The antenna was fabricated using a Rogers 4003 substrate, utilizing an accurate photolithographic etching process. Figures 7(a) and 7(b) show the top and bottom views of the fabricated antenna prototype, respectively. The experimental setup is depicted in Fig. 7(c) -Figure 7(e). The comparison between simulated and measured |S₁₁|, gain, and axial ratio are shown in Fig. 8(a)-Figure 8(c). The measured |S₁₁| has a bandwidth of 1.2 GHz (31.9–33.1 GHz).

The gain and axial ratio (AR) displayed in Figs. 8(b) and 8(c) exhibit good agreement between simulated and measured results. The measured peak gain is 7.05 dBi, with an observed ARBW of 0.3 GHz (32.5–32.8 GHz). The far-field radiation patterns (φ = 0⁰ and φ = 90⁰ planes) for the described antenna at 32.6 GHz are shown in Fig. 9. In both planes (φ = 0⁰ and φ = 90⁰), the antenna offers an almost omnidirectional radiation pattern. To demonstrate the benefits of the proposed work, a comparative analysis has been performed against similar work in the current literature, as shown in Table 2. The comparison covers the antennas' geometrical structures, the extent of size reduction achieved, operational bandwidth, gain, and circular polarization. Based on the findings presented in Table 2, it can be noted that the dimensions of the proposed antenna layout are more compared than Refs. [32], [33], [34], and [35] while the operational bandwidth and gain are very good. The antennas presented in Refs. [31], [36] and [37] are more compact than the proposed antenna but they suffer from lower gain and bandwidth. None of the antennas discussed in Refs. [31]-[37] exhibit circularly polarized radiation.

Table 2

Comparative analysis with the existing literature
Ref.	Antenna Geometry	Volume (mm³)	Size Red. (%)	fr (GHz)	Bands (GHz)	BW (GHz)	Gain (dBi)	Cir. Pol.	Applications
[31]	Dipole	10×18×0.254 (45)	< 32	32	26.5–38.2	11.7	4.5–5.8	No	5G
[32]	Slotted	20×16×0.508 (162)	> 63	28	26.5–32	5.5	8–9	No	5G
[33]	Vivaldi	NA	NA	26, 28	20–30	10	7	No	5G/RFEH
[34]	Phased Array	41.5×4×0.508 (84)	> 29	25	20-28.5	8.5	7.8-9	No	5G
[35]	Bowtie	9.2×8.7×1.54 (123.2)	> 51	29.5	25.8–40.1	14.3	10.4	No	WPT
[36]	Modified Circular Patch	6×6×0.1 (3.6)	---	30.5	29-32.2	3.2	5.6	No	NA
[37]	Ink-Jet Printed	12.06×12.06×0.18 (26.1)	< 128	24	23.8–24.5	0.7	5	No	RFEH
[38]	Slots-notched Rect. Patch	12.4×6×0.8 (59.5)	----	32.6	31.7–33.2	1.5	7.2	Yes	5G/RFEH
NA: Not Available, BW: Bandwidth, Size Red: Size reduction, fr: Resonant frequency, WPT: Wireless Power Transfer

A high-gain broadband monopole antenna has been successfully designed and investigated. The performance characteristics such as resonating frequency, operating bandwidth, gain, and axial ratio of circular polarization have been examined. Several parametric studies have been carried out to investigate the performance behavior. The reported antenna operates at 32.6 GHz with a reflection coefficient of -24.8 dB bandwidth of 1.5 GHz (31.7–33.2 GHz). and circular polarization properties with a maximum gain of more than 7.8 dBi. Therefore, it has been concluded that the reported antenna is suitable for mm-wave 5G communications.

Ethical Approval:

Not Applicable

Funding

This work was partly supported by the Science and Engineering Research Board (SERB) under the VAJRA Scheme under Grant VJR/2019/000009.

Author Contribution

Authors Contributions:Mamoni Saha and Daasari Surender conceptualized the work and wrote the manuscript.Taimoor Khan and Fazal Ahmed Talukdar supervised and reviewed the work.Sembiam R. Rengarajan, Ahmed A. Kishk and Yahia M.M. Antar reviewed and edited themanuscript.

Availability of data and materials:

Not Applicable

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No competing interests reported.

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Slot-Notch Mechanism Enabled Circularly Polarized High Gain Antenna for 5G mm-Wave RF Energy Harvesting

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Abstract

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1. Introduction

2. Antenna Design and Performance Characteristics

3. Experimental Analysis

Conclusion

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Funding

Author Contribution

Availability of data and materials:

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