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Inverted K-shaped antenna with partial ground for THz applications

Usha Keshwala, Sanyog Rawat, Kanad Ray

PII: S0030-4026(20)30928-1
DOI: https://doi.org/10.1016/j.ijleo.2020.165092
Reference: IJLEO 165092

To appear in: Optik

Received Date: 3 April 2020

Accepted Date: 7 June 2020

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Inverted K-Shaped antenna with partial
Ground for THz applications

Usha Keshwala1, Sanyog Rawat2, and Kanad Ray3

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1
ECE, Amity University, Noida, India
2
ECE, Manipal University Jaipur, India
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ASAP, Amity University Jaipur, India
Corresponding author: Sanyog Rawat (sanyog.rawat@gmail.com)

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Abstract

This article presents design and analysis of inverted K-shape super wideband antenna for Terahertz
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frequencies. The initial design of square patch antenna is modified to inverted K-shaped antenna
(proposed prototype) by inserting triangular slots in the patch. The parametric analysis is carried out for
the partial ground size optimization and impedance bandwidth is enhanced by etching slots in the antenna
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patch, thus making it inverted K-shape. In addition to wide bandwidth a very high gain of 22.1dB is
obtained at 8.8 THz.

Keywords
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K- Shaped antenna, Square Patch antenna, Partial Ground.

Introduction
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Wireless communication technology has undergone unprecedented increase in demand for high data rates
with high spectral efficiency and strong wide-band fading reduction over the last few years. The data
traffic has increased in wireless domain dramatically due to a change in the way information
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continuously generated, exchanged, and handled by today's society. In order to handle these
tremendous data rates, new spectral bands will be required due to the scarcity of available
spectrum for wireless communication [1]. These led to WC (Wireless Communication) beyond
microwave frequency i.e. THz (Terahertz) and Sub-THz communications, which covers the 0.1-
10THz unallocated frequency band. Terahertz band can be utilized for high data rate (10 Gbps-
Giga Bits per Second) within short distance up to10m [2]. The electromagnetic spectrum at
terahertz (THz) system is rich in unique features for screening for weapons, low transmission
power, explosives and bio-hazards, imaging of hidden objects, water content, and skin, wide
bandwidth and scaled-down system dimensions, high resolution and these benefits can be
exploited by utilizing the efficient THz sources and detectors [3-6].

The size of an antenna reduces to sub millimeter at Terahertz frequencies [7]. Due to
advancement in photonics and semiconductor devices which are operating at terahertz frequency
the realization of these sub millimeter systems is possible. Short communication distance is the
main constraint at terahertz frequency which is imposed due to very high path loss at these
frequencies. Typically, the depth of penetration is lower than that of the microwave radiation,
thus the applications extend to the checking of hidden defects/faults, non-uniformity and crack
on the material surface [8].To mitigate this constraint various high gain THz antennas have been
designed [9-12]. In [9-10] GaAs membrane supported THz dipole antenna with high input

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impedance is proposed to improve the efficiency of THz photo mixer. In [10] high input
resistance Yagi-Uda antenna designed on very thin substrate is presented for THz frequency. An
Elliptical ring shaped antenna of size 800μm x600μm with impedance bandwidth ranging from

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0.3-9.3THz is presented for terahertz applications [11]. A similar kind of hexagonal fractal
antenna is presented for terahertz application for the frequency range of 0.2- 11.5 THz [12].

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In this paper a simple inverted K-shaped antenna is presented for Wireless body area Network
(WBAN) at THz frequencies. The evolution of antenna designs are divided in to three stages i.e.
Antenna 1, antenna 2 and antenna 3(Final proposed design). In section I evolution of antenna
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design is presented and in Section II the concerned results are discussed.

I. Evolution of Antenna Design

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The proposed antenna is made of polyamide substrate and PEC as patch and the conducting
ground plane. The antenna is 600 x 600 μm2 and fed by microstrip line as can be seen from
Fig.1.The evolution of proposed antenna is shown in Fig.2. The initial antenna (antenna 1)
design is started with simple rectangular patch with dimensions of 400 x 315μm as appears in
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Fig. 3(a). The lower cut off frequency is calculated as follow by equating the areas of cylindrical
monopole antenna and rectangular patch antenna [13].
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Fig. 1 Proposed geometry (a) front view (b) Rear View

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Fig.2 Antenna evolution stages
𝑐 7.2
𝑓𝑙 =𝜆 = (𝐿+𝑟+𝑝) 𝐺𝐻𝑧 (1)

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Where, L is the height of the patch antenna in cm (equivalent to height of cylindrical monopole
antenna), the effective radius of equivalent cylindrical monopole antenna is r cm, and the feed

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line length is p. If L is the length of the rectangular patch and W is the width of the rectangular
patch then the L and r of the cylindrical monopole is calculated as follow.
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𝐿=𝑊 (2)

𝐿
𝑟= (3)
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The final dimensions of an antenna is outlined in Table 1.Thus by considering the final
optimized dimensions of an antenna presented in Table 1 lower cut off frequency obtained is
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0.13 THz. It can be clearly seen from the Fig. 3(b) (variation in the return loss characteristic) the lower
cut-off frequency is 0.11THz.

II. Results and Discussion

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The parametric analysis is carried out for the selection of ground length and concerned return
loss variation as shown in Fig. 4.
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Table 1 Optimized parameters of an antenna

Symbols Values (μm) Symbols Values (μm)

Ws 600 p 185
Ls 600 L1 141.421
W 400 t 100
L 315 Lg 130
Wf 130 L2 115
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Fig. 3 (a) square patch antenna (b) return loss (S11) variation with frequency

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Fig.4 Return loss variation with frequency for various ground size

The conventional square patch (antenna 1) is altered to antenna 2 by inserting two symmetric
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triangles (right angle triangles) and by etching rectangular shape at the top of square patch as
shown in Fig. 5(a). The impedance bandwidth is improved as compared to antenna1 as shown in
Fig 5(b).
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Fig.5 (a) Geometry of antenna 2 (b) Return loss variations with frequency

The radiating patch of final antenna consists of inverted K shape structure, formed from the basic

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square patch monopole antenna. The Antenna 2 is modified to antenna 3(the final proposed
antenna) by inserting triangular slot in the antenna 2.Thus the antenna design obtained is inverted
K shaped structure. The angle in the K shape patch is kept 900.After adding triangular slot in the
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patch the impedance bandwidth is increased significantly as depicted in Fig 6. The antenna
covers bandwidth from 0.46-8.84THz shown in the return loss variation graph for antenna 3. Fig.
7 presents the VSWR and gain of the antenna. The antenna has very high gain of 22.1dB at 8.8
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THz frequency and VSWR<2 in the obtained impedance bandwidth.

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Fig. 6 Return loss variation of proposed antenna

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Fig. 7 Gain and VSWR variation of proposed antenna

In addition to VSWR, gain and return loss characteristics, radiation efficiency and radiation

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pattern are introduced in Fig.8. The radiation efficiency of antenna varies between 0.72 and 0.93.
The maximum radiation efficiency is obtained as 0.93 at 1.75 THz and maximum total efficiency
is obtained as 0.92 at 1.75 THz. The radiation patterns of an antenna at 3 THz, 6THz, and 9 THz
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are presented in Fig. 9. At 3 THz frequency the main lobe is at 3550 and 550 in E- field and H-
field respectively. The shift in the main lobe is observed as 00 and 1000 at 6 THz for the E and H-
field respectively. The directions of main lobes remain same for E-field at 9 THz and slightly
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shift at 950 for H-field as shown in Fig 9.

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Fig. 8 Radiation and total efficiency of proposed antenna

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(a) (b)

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(c)
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Fig. 9 Radiation Patterns of proposed antenna

Conclusion
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An inverted K shaped antenna with defected ground structure is proposed for Terahertz (WBAN)
applications. The antenna achieves very wide impedance bandwidth of 0.46-8.84 THz in addition
to high gain of 22.1 dB at 8.8THz. The bandwidth is enhanced as compared to initial square
patch antenna by etching triangular slots in the square patch and modifying prototype to inverted
K-shaped antenna. The simple structure, wide bandwidth, and high gain make an antenna
appropriate for terahertz (WBAN) applications.
Declaration of interests

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.

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