A novel gold and SiO2 material based planar 5-element high HPBW end-fire antenna array for 300 GHz applications

Jagadeesh Babu Kamili; Rabah W. Aldhaheri; Anveshkumar Nella; Khalid H. Alharbi; Muntasir M. Sheikh

doi:10.1515/phys-2024-0116

Article Open Access

A novel gold and SiO₂ material based planar 5-element high HPBW end-fire antenna array for 300 GHz applications

Jagadeesh Babu Kamili , Rabah W. Aldhaheri , Anveshkumar Nella , Khalid H. Alharbi and Muntasir M. Sheikh

Published/Copyright: January 31, 2025

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From the journal Open Physics Volume 23 Issue 1

Abstract

This article is intended to propose a novel gold and SiO₂ material based planar 5-element high half power beam-width (HPBW) end-fire antenna array for 300 GHz applications. The proposed radiating structure composes of a 5-element off-set feed rectangular patch antenna array fed by a tapered microstrip line to accomplish high HPBW. Off-set feeding and parasitic patch resonators are incorporated to access the end-fire radiation characteristics. This antenna operating frequency ranges from 277.5 to 315 GHz with a peak gain and HPBW of the antenna as 4.98 dBi and around 100°, respectively, at 300 GHz, making it a good radiator at the specified band. A gold material of thickness 5 μm is used as the metal, while the SiO₂ with a thickness of 60 μm is adopted for the substrate material. Design, parametric analysis, and lumped element circuit models are also explored in this work. End-fire pattern, high HPBW, and good performance make this antenna to be eligible to use in THz applications such as imaging, scanning, communication, and bio-medical.

Keywords: end-fire antenna array; gold; HPBW; off-set feed; radiation pattern; SiO2

1 Introduction

Nowadays, terahertz (THz) frequency radiation has grabbed significant attention for its high data rates in wireless communications. Therefore, many broadband communication systems are currently being developed in the THz frequency range [1,2,3,4,5,6]. But Lossy propagation and high-power shortage are the issues associated with the THz frequencies. Antennas radiating in end-fire direction find several applications in the present advanced wireless communications. The short pulses, ultra-high-frequency carriers, and the very high bandwidth of the THz spectrum are able to revolutionize the today’s wireless communication by achieving maximum data rates of 100 GB/s [4]. As a result, the wireless data traffic, which is increasing exponentially, can be solved significantly [5]. Since THz frequencies have extremely small wavelengths and coherent non-ionizing property, the techniques used at THz are useful to facilitate high-resolution imaging and positioning, mainly for security and scanning the human body [6].

In the mentioned THz systems, the end-fire radiation antennas are the vital components to launch the electromagnetic energy into free space. A few finest end-fire antennas such as traveling wave antennas, Yagi-Uda antennas, substrate-integrated waveguide (SIW) antennas, and horn antennas, exist at THz bands as well. Horn antennas, which have advantages of simple structure, high gain, and wide band characteristics, have been reported in the literature at THz bands [7,8,9,10,11]. A 3D horn antenna that operates at 325–500 GHz was proposed in Fan et al. [9]. The radiation aperture of the horn antenna in E-plane and H-plane was enlarged for enhancing gain by employing a quasi-planar reflector. A dual polarized horn antenna was reported in Liang et al. [11]. To increase the impedance matching in its operational frequency band (i.e., 220–330 GHz), effective medium lens was introduced. Reported horn antennas at THz frequencies require complex fabrication procedures such as deep reactive ion etching and computer numerical control matching. Moreover, integration with other planar terahertz components is difficult as waveguides are used for exciting them.

SIWs are also used for microwave applications similar to waveguides. This technology is applied to design antennas with end-fire radiation at microwave and millimeter wave frequencies [12,13,14,15,16]. An end-fire SIW antenna, which operates at 26.6–38.7 GHz, was proposed in Li and Chen [13]. It achieved wideband characteristics by loading two face rectangular-shaped patches, which act as a meta-surface. A SIW antenna with circular polarization characteristic at Ka band was reported in Wang et al. [15]. Two antipodal notches were etched to make a complementary source. Also, to increase the gain of the antenna in the end-fire direction, a dielectric rod-like structure was loaded. Even though the SIW antennas have some advantageous characteristics at microwave and millimeter wave frequencies, they are very difficult to fabricate at THz frequencies due to the presence of metallic vials. Hence, they are very limited at THz frequencies.

Another category of antennas known for generating end-fire radiation are Yagi-Uda antennas [17,18,19,20]. In the study by Deal et al. [17], a novel quasi-Yagi antenna is proposed using active planar array method. They comprise many directors, a reflector, and a driven element. This antenna achieves a measured 48% frequency bandwidth with 12 front-to-back-ratio (FBR), and less than-15 dB cross-polarization, and 3–5 dBi of absolute gain. In the study by Hu et al. [18], a vertically polarized top hat monopole Yagi-Uda antenna that operates at 0.55 GHz was presented. The folded top hat monopole acts as a driven element, whereas the four short-circuit monopoles act as directors. A Yagi-Uda antenna, which has an impedance bandwidth of 10 GHz, was presented in Pavanello et al. [19]. A transition balun, which originates from a co-planar waveguide to a co-planar strip-line at a frequency of 300 GHz, is used to excite the antenna. Moreover, the antenna was planar and was fabricated on a cyclic olefin co-polymer film, which has a thickness of 100 µ m. In the study by Wang et al. [20], a compact shared aperture antenna with high isolation characteristics is developed. The antenna is shown to give a peak radiation efficiency of 80%. This antenna uses the concept of combining monopole and dipole concept involving reconfigurable concept.

Another class of antennas that produces end-fire radiation is traveling wave antenna. It is generally based on a condition given by Hansen-Woodyard. The propagation constant of the antenna is typically needed to be more than the free space wavenumber slightly [21,22,23,24,25]. In the study by Hou et al. [22], a periodic leaky wave antenna with air as substrate is fed by a microstrip line. It has end-fire radiation characteristic and phase constant is manipulated by employing multiple monopoles. A traveling wave antenna was proposed in the study by Ge et al. [24] with end-fire radiation characteristic. It comprises crossover structures for phase reversal and satisfies the Hansen-Woodyard condition. As a result, it radiates electromagnetic energy into the free space constructively in the end-fire direction. The above-mentioned traveling wave antennas and Yagi-Uda antennas have some drawbacks such as limited bandwidth, complex 3-D geometries, and delicate structures with very thin substrates. Some other related works are also discussed in the available literature [26,27,28,29,30,31,32]. Moreover, none of the reported antenna structures in the literature has high HPBW. Hence, this article proposes a novel compact, lightweight, cost-effective, simple planar, and high performance 5-element off-set feed high HPBW end-fire antenna array for 300 GHz applications. This design adopts novelty by constructing a radiator with 5-element off-set feed rectangular patch antenna array fed by a tapered feedline to obtain high HPBW. This article is organized as follows: Section 2 reports the proposed antenna design, performance characteristics, equivalent model, and discussion. Section 3 presents the design steps, parametric variation, and results analysis. Section 4 concludes the work.

2 Proposed high HPBW antenna structure

In this design, gold of thickness 5 µm and silicon dioxide (SiO₂) of thickness 60 µm are used as metal and dielectric substrate, respectively. Top and bottom layers of the proposed antenna are shown in Figure 1(a) and (b), respectively. Overall dimensions (L × W) of the antenna are 1.25 × 1.3 mm².

Figure 1

Proposed antenna: (a) top view and (b) bottom view.

In the radiating structure, each patch element (L _p × W _p) is of size 0.075 mm × 0.15 mm, while the feed line length (L _f) is 0.125 mm. Each parasitic resonator (L _r × W _r) is with 0.05 mm × 0.1 mm, and partial ground has a length (L ₁) of 0.16 mm. Spacing between the parasitic elements along horizontal direction (h) is 0.135 mm, while that along vertical direction (v) is 0.2 mm. All the specified dimensions are mentioned in Table 1.

Table 1

Dimensions of the proposed antenna

Parameter	W	L	W _r	L _r	L _f	L ₁	v	h	a	b	f
Size (mm)	1.3	1.25	0.1	0.05	0.125	0.16	0.2	0.135	0.085	0.15	0.002

The scattering parameters of this developed antenna are presented in Figure 2. Figure 2 depicts that the antenna is operating in a frequency range between 277.5 and 315 GHz with a resonant frequency at 300 GHz.

Figure 2

S₁₁-parameter of proposed antenna.

3D-radiation pattern is shown in Figure 3(a), while the 2D-pattern is shown in Figure 3(b). The 3D-pattern in Figure 3(a) presents a peak gain of 4.98 dBi at 300 GHz with end-fire radiation pattern. The 2D-pattern in Figure 3(b) reveals high HPBW of around 100°. Surface current distribution on the proposed antenna at 300 GHz is also shown in Figure 4. Hence, it is evident that the strong surface currents are almost residing uniformly in the patch antenna array elements.

Figure 3

Radiation patterns at 300 GHz: (a) 3-D and (b) 2-D.

Figure 4

Surface current distribution at 300 GHz.

A lumped element equivalent model of the proposed antenna is shown in Figure 5. This circuit model is developed on the basis of conventional approach to approximate a microstrip antenna using R, L, and C model. In general, the feed line is assumed as a series combination of R and L. The antenna radiator is denoted using a series combination of R, L while a parallel combination of R, L, and C is considered between the top and bottom planes. Hence, in the proposed 5-element antenna array, each element is represented using a series R, L and a parallel R, L, and C, as shown in Figure 5(a). Moreover, each antenna element is terminated with a free-space impedance of 377 Ω. The equivalent model design, optimization, and performance study are executed using ADS tool. The quality of the presented image can be enhanced using the image pre-processing techniques such as discussed in the study by Versaci et al. [33], where fuzzy logic is used for better image quality. However, for brevity, the lumped model of the image is presented here. In this model, each parameter is tuned over a range of values so that overall model S-parameter performance matches with the antenna performance as shown in Figure 5(b). From the figure, it is observed that S₁₁-parameter values of both simulated and equivalent circuit model take same resonance, however giving different impedance bandwidth values.

Figure 5

(a) Proposed antenna equivalent circuit model and (b) S-parameter performance.

3 Design steps and parametric study

This section presents the design steps to realize the proposed antenna. This process follows three design steps. In the Design 1, an off-set fed monopole antenna with parasitic patch elements is designed with a tapered microstrip feed line as depicted in Figure 6(a) and (b). Off-set feeding mechanism is used to obtain the directional pattern in end-fire direction, while the parasitic patch elements are used to enhance the gain of the antenna. In the radiating structure, the patch element (L _p × W _p) is of size 0.09 mm × 0.185 mm, while the feed line length (L _f) is 0.125 mm. Each parasitic resonator (L _r × W _r) is with 0.05 mm × 0.123 mm, and partial ground has a length (L ₁) of 0.145 mm. These dimensions are noted to obtain the resonant frequency at 300 GHz as shown in Figure 7. The Design 1 radiation 3D and 2D patterns are shown in Figure 8. Peak gain of the antenna with this configuration is 8.58 dBi, as illustrated in Figure 8(a). Figure 8(b) also reveals that the pattern has less HPBW noting a narrow directional pattern. But the main objective of this design is to enhance the HPBW.

Figure 6

Evolution design steps (a) and (b) Design 1 (c) and (d) Design 2 (e) and (f) Design 3 (proposed antenna).

Figure 7

Reflection coefficient performance of the design steps.

Figure 8

Radiation patterns at 300 GHz for Design 1: (a) 3-D and (b) 2-D.

Hence, Design 2 is enhanced by adding three rectangular radiators using a tapered microstrip line, as depicted in Figure 6(c) and (d). In the radiating structure, the patch element (L _p × W _p) is of size 0.075 mm × 0.148 mm, while each parasitic resonator (L _r × W _r) is with 0.05 mm × 0.097 mm. A total of nine parasitic patch elements are used to get end-fire radiation characteristics. The -10 dB reflection coefficient bandwidth achieved with this configuration ranges from 280 to 313 GHz, as shown in Figure 7. The Design 2 radiation 3D and 2D patterns are shown in Figure 9. Peak gain of the antenna designed with this configuration is 7.03 dBi, as illustrated in Figure 9(a). It can be observed that the HPBW is enhanced, as depicted in Figure 9(b), due to the deployment of three patch elements. To further increase the HPBW, five rectangular radiators are fed by a tapered microstrip line, as depicted in Figure 1(a).

Figure 9

Radiation patterns at 300 GHz for Design 2: (a) 3-D and (b) 2-D.

An important observation in this present work is the study of S₁₁-parameters on ground length variation and material changes. The impact of ground length L ₁ on the variation of S₁₁-parameters is studied and portrayed in Figure 10. From the figure, it is obvious that for L ₁ = 0.16 mm, better reflection coefficient values are obtained compared to the other values of L ₁ such as 0.1, 0.125, 0.15, and 0.175 mm. Hence, in the design of this antenna, the value of L ₁ considered is 0.16 mm, giving better return loss. Another important parameter to study in the present work is to know the impact of material selected on the reflection coefficient values of the designed antenna as the chosen material may affect the antenna’s radiation properties at THz frequencies. The variation of S₁₁-parameters on the material used in the antenna is presented in Figure 11. From the figure, it is clearly seen that at the chosen THz frequencies, the material has almost no impact on the reflection coefficient values, and hence, in this study, gold is selected in the design of the antenna.

Figure 10

S₁₁-parameter variation w.r.t ground length (L ₁).

Figure 11

S₁₁-parameter variation w.r.t to metal.

The proposed work is compared with some existing antennas in the literature as in Table 2. In the study by Ohno et al. [26], a novel phased array of dielectric cuboid is designed at 300 GHz having a size of 1 mm × 5.5 mm. In the study by Rey et al. [27], a phased array of horn antenna operating at 300 GHz is designed. The antenna has an overall size of 3 mm × 3.5 mm with HPBW of 20°. In the study by Yamada et al. [28], another cuboid antenna operating at 300 GHz is designed with a size of 1.36 mm × 1.36 mm and HPBW of 25°. In the study by Zheng et al. [29], a 130 nm × 130 nm sized SiGe patch antenna operating at 300 GHz is designed and developed. In the study by Ishihara et al. [30], lens-based dielectric antenna with 10 mm × 10 mm dimension is designed. The proposed antenna covers the band 277.5–315 GHz with dimensions 1.25 mm × 1.3 mm, and HPBW of 100° is designed and developed.

Table 2

Comparison with existing works

Ref.	Technique used	Resonant frequency (GHz)	Dimensions	HPBW
[26]	Dielectric cuboid	300	1 mm × 5.5 mm	17.6°
[27]	Horn antenna	300	3 mm × 3.5 mm	20°
[28]	Dielectric cuboid	300	1.36 mm × 1.36 mm	25°
[29]	SiGe patch	300	130 nm × 130 nm	—
[30]	Dielectric lens antenna	270	10 mm × 10 mm	7.4°
[31]	On chip horn	300	1 mm × 1.5 mm	20°
[32]	Vivaldi antenna	292	1.8 mm × 0.76 mm	—
This work	Microstrip patch	300	1.25 mm × 1.3 mm	100°

4 Conclusion

A novel planar HPBW 5-element end-fire antenna array for 300 GHz applications has been presented. It has a fractional bandwidth of 12.6% and a peak gain of 4.98 dBi. Design steps, parametric variation, and equivalent circuit model have also been presented. It is very advantageous at 300 GHz applications where high HPBW and end-fire radiation patterns are major concerns. Moreover, the antenna design is simple, planar and obtains good directional performance. Hence, the structure can find its THz applications, including THz imaging, scanning, communication, and security.

Funding information: This work was funded by the Deanship of Scientific Research (DSR) at King Abdulaziz University, Jeddah, Saudi Arabia, under Grant No (RG-46-135-42).
Author contributions: The conceptualization, simulation, and experimental part were carried out by A. K. N. Conceptualization, methodology, and supervising the research were done by R. W. A. The manuscript preparation and part of simulations were carried out by J. B. K. Result validation and formal analysis were carried out by K.H.A. and M.M.S. All authors have read and agreed to the published version of this manuscript, design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Conflict of interest: The authors state no conflict of interest.
Data availability statement: All data generated or analyzed during this study are included in this published article.

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Received: 2024-10-01

Revised: 2024-11-26

Accepted: 2025-01-10

Published Online: 2025-01-31

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/phys-2024-0116

Keywords for this article

end-fire antenna array; gold; HPBW; off-set feed; radiation pattern; SiO2

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