Design and Performance Investigation of Miniaturized Multi‐Wideband Patch Antenna for Multiple Terahertz Applications

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Abstract

In this paper, a highly efficient multiband optimized slotted pentagonal terahertz patch antenna and its 2 × 2 multi-input multi-output (MIMO) planar array is proposed for multiple terahertz (THz) applications like high-speed indoor communications, explosive detections, arms detection, medical imaging, pharmaceutical analysis, and industrial inspections, etc. Here, the proposed patch antenna is developed from the simple rectangular patch antenna (SRPA) by optimizing the shape of radiating patch and ground plane. Such proposed antenna is designed on the transparent polyimide substrate material having a dielectric constant of r = 3.5 and thickness 21.5 µm. The particle swarm optimization (PSO) technique is used to enhance the performance parameters of proposed antenna. The performance parameters like reflection coefficient, gain, directivity, radiation pattern, and antenna efficiency are computed at the resonating frequencies of proposed antenna. It covers wide bandwidth, which resonates at 3.00 THz, 4.85 THz, 7.02 THz, 8.87 THz, 9.43 THz, and 10.785 THz frequencies having reflection coefficient less than −10 dB. It is also noted that as compared to early reported THz antennas, it has achieved a maximum gain of 13.92 dB and radiation efficiency of 85.77% within the resonating band. Also, a 2 × 2 MIMO antenna array is designed using an optimized antenna element for more effective terahertz communication. The performance of such MIMO array is computed in terms of the transmission coefficient, envelope correlation coefficient (ECC), and Mean effective gain. It has achieved <−15 dB isolation between the antenna elements. The proposed antenna could be a successful choice for multiple terahertz applications.

Introduction

Terahertz (THz) identifies the segment of the electromagnetic spectrum between the microwave region and the infrared field. It ranges within the 0.1–30 THz frequency band. The huge bandwidth delivered by the THz band opened the door to several applications that require high data speeds. The high-speed wireless communication requirements are increasing day by day, so researchers from both the academic community and industry have started research into higher frequency bands and attempted to deliver wireless communication within the unassigned terahertz frequency range [1], [2], [3]. Besides providing high-speed and broadband communications, THz radiation is helpful in a wide variety of fields including explosive detections, weapons detection, medical imaging, pharmaceutical research, and industrial inspections. Devices based on THz technologies can see through hurdles such as plastic, clothes, and creased cardboard. These radiations help to detect dangerous materials, conceal arms, and synthetic drugs. THz radiations are effectively reflected by non-metals and non-polar devices upon exposure, and this property of THz radiations makes it ideal for many security and informatics applications [4], [5]. So, after knowing this wide range of applications in the THz spectrum, there is a need to develop a new highly efficient multiband and wideband antenna that can support these high THz frequencies efficiently. But there is always some obstacle for wireless communication in the high THz regime like high attenuation, Multipath fading, absorptions, and path loss are the factors limiting the boundless use of THz technology. These obstacles diminish the quality of the signal and cause serious errors in any communication channel [6], [7]. Due to its unique features, including compact size, minimal volume, and ease of production, printed antennas are widely used in wireless connectivity components. Given these highlights, scientists concentrated on printed planar antennas which can be utilized for wireless communication purposes in the THz zone. Printed planar antennas did a tremendous job in advancing antenna innovations in wireless communications networks [8], [9]. Many terahertz single-band antennas and arrays have already been developed to combat the attenuation effects with good signal efficiency and wide spatial coverage. The single antenna, however, exhibits the same capacity as the antenna arrays, because all radiating elements are fed with a single port. In comparison to single port antennas, MIMO antennas manage multi-path propagation with a higher data rate, greater performance, and more reliability. MIMO system has multiple antennas for transmitting and receiving sides to increase the efficiency of the radio link. It also overcomes the consequences of multipath fading in various communications [10]. Multiple approaches to design a THz band antenna for THz applications are previously published [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29] in the literature. The antenna prototypes operating on THz band having a low gain and narrow bands are not sufficiently qualified to deal with environmental and propagation losses. A few numbers of high gain antennas are developed by some experts to alleviate the problems of attenuation loss [11], [12], [13], [14], [15], [16], [17] such as the Yagi-Uda antenna, leaky-wave antenna, superstrate, and metamaterial-based antenna, substrate integrated waveguide antennas, log-periodic micromechanical antenna, and lens antenna. All the above-mentioned configurations had massive and complicated three-dimensional geometries that cannot be easily fabricated and integrated with the on-chip integrated circuits. Thus, the geometries of the planar microstrip antennas are known as the most suitable antenna structures for the THz devices. There are several planar antenna geometries [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29] that are already listed in the available literature for terahertz applications. A single band planar antenna has been investigated by Temmar et. al in Ref [18] for THz applications by using the synthesized photonic bandgap substrate material and attain a maximum gain of 7.3 dB. Kushwaha et al. [19] investigated the performance of a highly effective dual narrow-band antenna and achieved a maximum gain of 7.94 dB for THz applications. Dhillon developed a planar antenna at resonant 0.63 THz frequency by using the polyimide substrate and achieved 7.93 dB gain for defense applications [20]. For vitamin K2 detections, Prince et al. [21] registered a single band printed antenna at a resonance frequency of 3.356 THz within 5.23 dB gain. Mrunalini et al. design and investigated a dual-band reconfigurable antenna at 2.17 THz and 2.58 THz frequency by utilizing the graphene as conducting material and attain a peak gain of 5.03 dB for wireless THz applications [22]. Shahid et al. introduced a single band highly efficient planar THz antenna by utilizing photonic bandgap material with defective ground structures (DGS) and attain a maximum effective gain of 6.793 dB at resonant frequency 0.696 THz [23]. Singh proposed a multiband antenna using a photonic band structure that resonates with a peak gain of 10.5 dB at the THz frequency [24]. Goyal et al. [25] design and analyzed a dual-band planar antenna configuration using a graphene patch on the transparent substrate material and achieved a peak gain of 6.05 dB and a maximum bandwidth of 15.09%. Hossein and Behbod had developed a highly efficient wideband THz antenna having a bandwidth of 118% (0.434–1.684 THz) and a maximum gain of 5.72 dB [26]. Bansal et al. [27] and Singhal [28] developed and investigate the performance of wideband, high-gain THz planar antennas but neglected to measure important parameters like antenna efficiency. Cheng et al. [29] improved planar antenna gains by using the metamaterial-based superstrate epsilon-near-zero and observed that the antenna gain is enhanced from 5.37 dB to 7.79 dB. The various strategies such as photonic bandgap (PBG), electronics bandgap (EBG), DGS, multilayered structures, nanoribbon wires, and complex multilayer substrate material are being used to maximize antenna's gain, bandwidth, and efficiency. But, adding these complex structures to planar antenna raises the antenna system's complexity and expenses. It is noticed from the literature that several antennas resonate on a singular or dual-band and suffer from low gain, limited bandwidth, and large size. Thus, such antennas are not suitable for multiple terahertz applications. Some researchers have achieved multi-band, high gain, and broad bandwidth, but did not bother with the antenna's efficiency that cannot be considered in this lossy environment.

This research paper is planned as the design, evolution, and optimization of the proposed antenna is discussed in the second section and the parametric analysis for a slot within the proposed antenna is discussed in the third section. The different performance parameters of the antenna are evaluated at THz frequency in the fourth section. A 2 × 2 MIMO antenna array for high-performance THz communications is designed in the fifth section and different results for MIMO antenna system are determined. In the last, a comparison between the previously reported antenna and the proposed antenna is done for terahertz applications.

Section snippets

Evolution and optimization proposed multi-wideband antenna

The multiband optimized slotted pentagonal patch antenna is developed in this section from a simple rectangular patch antenna (SRPA) for multi-wideband THz operation. The proposed antenna is modeled with the polyimide transparent substrate material having a dielectric constant of 3.5 and a thickness of 21.5 µm. The copper patch is used as a conducting material with conductivity 5.8×107s/m. The square shape substrate material having a size (90 × 90) µm and copper patch with a thickness of 0.5 µm

Parametric analysis of proposed optimized antenna

The parametric study is carried out to study the effect of pentagonal shape slot of proposed antenna on resonating frequency and gain. From Fig. 1(e), it is observed that the optimized proposed antenna is loaded with DGS and a pentagonal shape slot inside an irregular pentagonal patch. To find out the impact of slot on resonating frequency and gain, the width of slot i.e Sw is varied from 1 to 5 µm. On increasing the width, the side length of slot St will also increase. After the simulation,

Results and discussion

The proposed antenna is modeled, simulated, and optimized by using the highly powerful CST Microwave Studio. This planned antenna is analyzed by using a time-domain solver in CST. The rectangular waveguide port, which is the real port created through boundaries, is used to feed the antenna. The specific boundaries surrounding the waveguide port specify the EM distribution on the waveguide port and the EM waves emitted from the waveguide port. The Open (add space) boundaries are used which

Design of 2 × 2 MIMO antenna

In this section, the 2 × 2 MIMO antenna is proposed for terahertz applications. As it is discussed in Section 4, an optimized antenna design C is showing proper impedance matching, wider bandwidth, and high gain as compared to antenna designs A and B. So, the antenna design C is used for the MIMO antenna array.

To develop a 2 × 2 MIMO antenna, as shown in Fig. 8, the four irregular slotted pentagonal patches are assembled on a single substrate with a size (180 × 180) µm. By calculating the

State-of-the-art-comparison

In this section, comparisons between proposed optimized antenna design C with previously reported antennas have been done for terahertz applications. The comparison is done based on performance parameters like resonating bands, radiation efficiency, gain, bandwidth, and size of the antenna elements (see Table 4). In Refs. [19], [21], [23], [26], [29] the reported antennas are resonating at a single band but these are suffering from low gain, so it will diminish the quality of service of a

Conclusion

Current research work focused on the multi-band, small scale, large gain, and broad bandwidth THz frequency band antennas. Multi-band THz antenna can be used in applications like the detection of explosive material, sensing, spectroscopy, spacecraft, automobiles, and aerospace, etc. In this research, a compact-sized (μm) THz antenna is recommended which has been packed with high efficiency, gain, and directivity. In first designed antenna A, a planar pentagonal shape antenna is proposed having

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors would like to thanks the Visvesvaraya Ph.D. scheme, Meity (India) and Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India and for financial support under grant number EEQ/2019/000115.

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