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[1] Yi Huang Kevin Boyle, “Antennas From Theory to Practice”, John. Wiley & Sons Ltd., 2008. [2] Gibson, P.J., “The Vivaldi aerial,” Proc. 9th. Eur. Microwave.
SPACES-2018, Dept. of ECE, K L Deemed to be UNIVERSITY

Design of Flag-shaped 3-Element Array Antenna for Directive Radiation in Ku-Band Applications K. Venkata Reddy1, T. Venkateswara Rao1, T. Anilkumar2 1

Department of ECE, Sir C. R. Reddy College of Engineering, Eluru, India 2 Department of ECE, K L University, Guntur, India 1 [email protected] a frequency band from 81GHz to 95GHz and gain up to 18.5±1.3 dBiC is achieved [10].

Abstract— In this article, Antenna with flag-shaped radiating elements in antipodal configuration is proposed. The design and the study focuses on geometrical parameters like length of the patch, width of the flared structure to enhance the operability of the antenna in Ku-band spectrum. The proposed antenna is designed and simulated in ANSYS HFSS ver15.0 and the characteristic features obtained after simulation indicates that the antenna operates from 11.1293 GHz to 19.18 GHz. The proposed antenna is configured into an array with 3-elements. The characterization of antenna array is done in terms of return loss, isolation and radiation performance. The array configuration has improved the directive radiation performance.

This article proposed a model to design an antenna which is operable in Ku-Band spectrum and most suitable for the fore mentioned applications. II.

ANTENNA DESIGN

A. Antenna Geometry The proposed antenna consists of a square shaped substrate considered with FR4 substrate having dielectric constant 4.4. The dimensions of substrate are considered as small as 25x25mm2 with thickness of 1.6mm. Instead of employing the design of a conventional patch antenna, different approach is employed. Initially a rectangular patch with micro-strip line feed having 50 ohm characteristic impedance is designed on the top of the substrate. The feed line is connected along the left extreme end of the patch such that it looks like a flag shaped structure. The top and bottom conductors of the FR4 PCB are modeled; the bottom side of the PCB will have the same structure as the top side which is aligned in antipodal configuration. The evolution of the proposed antenna design is explained in the following iterations in Fig. 1. The geometrical parameters are tabulated in Table I.

Keywords— Vivaldi antenna, Ku-Band, directive radiation, antenna array.

I. INTRODUCTION The current day research is focused on implementation of compact wideband antennas which can be incorporated in portable and mobile wireless devices. In earlier days, the frequency spectrum has larger wavelengths which compelled to have antenna with larger dimensions. With the evolution of microwave spectrum, designers had the feasibility of designing antennas with compact dimensions. It’s a fact that as the wavelength decreases, the length of the resonator will have smaller lengths. This key point is often preferred to design compact antennas [1]. The current design employs the Vivaldi type of antennas used in linear array structure which was first invented by Peter Gibson [2]. The Ku-Band microwave spectrum is dedicated to applications such as Satellite Communication, Tracking and Data relay satellite, Space shuttle and Backhaul broadcasting [3].Several advantages of Ku-Band are more targeted coverage which avoids signal Interference from other communication systems [4].In [5], advantage of using Microstrip antenna operating at Ku-Band is explained. In [6], possibility of using different material with Micro-strip antenna providing Ku-Band applications is discussed.

a)

Iteration 1

b)

proposed model

Fig. 1 Evolution of Proposed Antipodal Flag Shaped (AFS) antenna geometry

The design and performance of a low cost, light weight, Flag shaped three element array is presented. Recently a lot of experiments have been made in array configuration of antenna which is briefly explained in [7]. Flag shaped antenna with 3 element array is capable to interact with tagged objects and hidden objects to exchange data with them [8]. The design is developed to operate at 2.45GHz. Antipodal antenna in array configuration [9] has achieved good impedance matching over

TABLE I. Parameter Value in mm

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PARAMETERS OF PROPOSED ANTENNA

Ls

Ws

h

Lp

Wp

a1

Lf

Wf

25

25

1.6

15

14.17

7.5

9

3.34

SPACES-2018, Dept. of ECE, K L Deemed to be UNIVERSITY These geometrical values tabulated in Table-I are optimized through parametric optimization which is discussed in the following section.

The modelling parameter is ‘a1’ and to study the behaviour its value is varied from 3.5mm to 7.5mm. A new type patch antenna having flag-shaped geometry with linear configuration having inter element distance of 15mm is proposed and analyzed using ANSYS HFSS ver15.0 for its quality parameter study.

B. Parametric Study The proposed antenna is designed with few variables which can decide the characteristics of the antenna. To study those effective parameters, length of the patch ‘Lp’, width of the flared structure ‘a1’ are varied.

It is observed that the increase in flaring width enhances the bandwidth. At lower values 3.5mm the return loss level is nearer to -10dB and offers the multiband pheneomenon. As the width increases the gap between the antipodal elements also increases thus enhancing the field distribution and contributes to bandwidth enhancement. The value ‘7.5mm’ is considered as optimum as it is covering the Ku-band which keeps the return loss level to a minimum of -31dB.

Case1: Effect of varying the length of the patch ‘Lp’ The length of the patch is a critical parameter which effects the resonant frequencies and cut-off frequencies in the return loss characteristics. The nominal value of 11mm is taken as length of the patch which offers more reflections for the excitation signal. Later, the parameter Lp is varied from 11mm to 15mm. The corresponding return loss variations are presented in Fig. 2.

Case3: Effect of length of flared patch ‘Lp’ Now the length of the antipodal patch elements is varied after flared structure is incorporated. The parametric study is conducted at 7.5mm flaring width.

Fig. 2 Parametric study on length of the patch S11 vs. frequency characteristics

Case2: Effect of varying the width of the flared structure ‘a1’

Fig. 4 Parametric study on length of the flared patch S11 vs. frequency characteristics

From the characteristics in the Fig.2 it is observed that the alignment of antipodal elements in a superimposed manner are separated through a dielectric substrate leads this kind of reflections and hence a flaring structure is incorporated for the both antipodal elements.

The parametric effects plotted in Fig.4 depicts that, at a constant flaring width, at 11mm patch length, the antenna operates under 12.54 GHz and extends beyond 20 GHz. At 13mm length, it makes the antenna to operate at 11.86 GHz and extends upto 20 GHz. The lower cut off frequency further shifted to the lower end to a value of 11.09 GHz and stops at 19.18 GHz. Thus at a constant flaring width, the increase in patch length tunes the operating band to range between 11 GHz to 18 GHz. The parameters considered here are optimized values since they provide the required solutions.Thus proposed structure operating between 11 GHz to 18 GHz is applicable to all Ku band applications.Flag shaped vivaldi antenna in antipodal configuration meets S11 < −10 dB criteria.

Fig. 3 Parametric study on width of the flared structure S11 vs. frequency characteristics

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SPACES-2018, Dept. of ECE, K L Deemed to be UNIVERSITY III.

IV. DESIGN OF 3-ELEMENT ARRAY

SIMULATION RESULTS

The Antipodal flag shaped patch antenna is configured into an array of 3-elements. The three elements are aligned back to back with the inter-element spacing of d = 15mm as shown in Fig. 7.

A. Return loss, Peak gain & directivity characteristics The return loss characteristics of proposed antenna are plotted in Fig. 5. The operating band of the antenna starts from 11.1293 GHz and stops at 19.1822 GHz. The minimum reflections are obtained at three frequencies at 12.8 GHz, 15.5 GHz, and 17.95 GHz where the achieved return loss values are -30.74 dB, -22.03 dB and -16.48 dB respectively. To compute the operating band of the proposed antenna, -10 dB return loss criteria is chosen.

Fig. 7 Fig. 5 Simulated return loss, peak gain & peak directivity vs. frequency characteristics of proposed AFS single element antenna.

Geometry of proposed 3-element linear array antenna.

The increase of the antenna elements will result in mutual coupling. The effects on return loss and isolation performance are plotted in terms of S-parameters in Fig. 8. The characteristics are simulated using individual excitation of antenna element.

The proposed antenna achieves maximum peak gain of 6.02 dB and maximum peak directivity of 7.09 dB at 15.85 GHz. The antenna maintains the average gain value of 5.05 dB and directivity of 6.08 dB throughout the band.

The characteristics shown in Fig. 8 clearly represents that the return loss characteristics of individual antenna elements also operates in the bandwidth ranging from 11-19 GHz that covers entire Ku-band. Moreover, the isolation characteristics are below -20 dB which is better than usual limit of -15 dB.

B. RADIATION PATTERNS OF THE PROPOSED ANTENNA The far-field characteristics of the proposed antenna are presented in three of its principle planes XY, YZ and XZ shown in Fig. 6. From the patterns, it is observed that the antenna has directive beam pattern and it is oriented towards the direction of propagation of the excitation signal. This indicates the provision of flaring structure in the antenna design facilitating the V-shaped notch which helps to concentrate the radiated energy through the flared structure. Finally, the antenna has the radiation pattern similar to the horn antenna having three resonant frequencies with similar characteristics are obtained.

Fig. 8 Simulated return loss and isolation vs. characteristics of proposed antipodal flag shaped antenna.

Fig. 6 2D-radiation pattern of proposed antipodal flag shaped antenna in principle planes.

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SPACES-2018, Dept. of ECE, K L Deemed to be UNIVERSITY Sir C. R. Reddy College of Engineering, Eluru for providing the licensed 3D EM simulation software ANSYS HFSS Vs. 15.0 and their esteemed guidance and support to the work.

The peak gain and directivity characteristics of the proposed 3-element array antenna are presented in Fig. 9 which shows the maximum values of 10.97 dB and 11.66 dB respectively observed occurring at 12.5 GHz and 13 GHz respectively. Whereas, the corresponding average values are maintained as 10.19 dB and 11.08 dB that represents the enhanced radiation performance of the single element antenna by transforming into array structure.

REFERENCES [1]

Yi Huang Kevin Boyle, “Antennas From Theory to Practice”, John Wiley & Sons Ltd., 2008 [2] Gibson, P.J., “The Vivaldi aerial,” Proc. 9 th Eur. Microwave Conf.,No.1,101-105,1979. [3] H. Liu, A. Qing, Z. Ding and C. Zhang, "Broadband circularly polarized antenna with high gain for Ku-band applications," 2017 International Applied Computational Electromagnetics Society Symposium (ACES), Suzhou, China, 2017, pp. 1-2. [4] A. S. Bhadouria and M. Kumar, "Wide Ku-Band Microstrip patch antenna using defected patch and ground," 2014 International Conference on Advances in Engineering & Technology Research (ICAETR - 2014), Unnao, 2014, pp. 1-5. [5] N. Misran, M. T. Islam, N. M. Yusob and A. T. Mobashsher, "Design of a compact dual band microstrip antenna for Ku-band application," 2009 International Conference on Electrical Engineering and Informatics, Selangor, 2009, pp. 699-702. [6] V.R. Tumati, Kolli. R and A. Tirunagari "Design of a Compact Wideband Bow-Tie Dielectric Stacked Patch Antenna for Ku-Band Spectrum," Computer Communication, Networking and Internet Security, Lecture Notes in Networks and Systems, Springer, Singapore, 2017. pp. 567-575. [7] V.R. Tumati and A. Tirunagari "Design and Study of Serially Fed Array Antenna for Ultra-Wideband Applications.", Lecture Notes in Electrical Engineering-434,Micro-Electronics, Electromagnetics and Telecommunications, Springer, Singapore, 2016, pp. 465-473. [8] L. Kouhalvandi, S. Paker and H. B. Yagci, "Ku - Band slotted rectangular patch array antenna design," 2015 23nd Signal Processing and Communications Applications Conference (SIU), Malatya, 2015, pp. 447-450. [9] Y. Yao, X. Cheng, C. Wang, J. Yu and X. Chen, "Wideband Circularly Polarized Antipodal Curvedly Tapered Slot Antenna Array for 5G Applications," in IEEE Journal on Selected Areas in Communications, vol. 35, no. 7, pp. 1539-1549, July 2017. [10] T. R. Rao, C. Sarath, N. Tiwari and R. Jyoti, "Design of SIW fed antipodal linearly tapered slot antenna array with hat-shaped dielectric loading for 60 GHz wireless communications," 2016 IEEE Indian Antenna Week (IAW 2016), Madurai, 2016, pp. 67-70.

Fig. 9 Simulated peak gain & peak directivity vs. frequency characteristics of proposed AFS antenna with 3 elements.

V. Conclusion Flag shaped Vivaldi antenna with linear configuration having inter-element distance of 15mm is proposed and analyzed using ANSYS HFSS simulation software. By making use of Antipodal configuration with variations in length of patch and width of flared structure, better simulation results in terms of Return loss, Gain, Isolation are obtained. The proposed antenna has a return loss of −31.5 db that ranges from 11.1293 GHz to 19.18 GHz that are compatible with Ku-band applications. ACKNOWLEDGMENT Authors would like to express their sincere gratitude to the Research Centre of Dept. of ECE and management of

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