Minkowski Fractal Circularly Polarized Planar Antenna for GPS Application

Minkowski Fractal Circularly Polarized Planar Antenna for GPS Application

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ScienceDirect Procedia Computer Science 00 (2018) 000–000 ScienceDirect

Available online at www.sciencedirect.com

Available at Science www.sciencedirect.com Procedia online Computer 00 (2018) 000–000

ScienceDirect

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Procedia Computer Science 143 (2018) 66–73

8th International Conference on Advances in Computing and Communication (ICACC-2018) 8th International Conference AdvancesininComputing Computing and (ICACC-2018) 8th International Conference on on Advances andCommunication Communication (ICACC-2018) Minkowski Fractal Circularly Polarized Planar Antenna for

GPS Application Minkowski Fractal Circularly Polarized Planar Antenna for GPS Application Salini Joya, Natarajamani Sa,*, S.M Vaitheeswaranb a b Department of Electronics and Communication Engineering Salini Joy , Natarajamani Sa,*, S.M Vaitheeswaran Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, India a

b CSIR-National Aerospace Laboratories, Bangalore, India Department of Electronics and Communication Engineering Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, India b CSIR-National Aerospace Laboratories, Bangalore, India a

Abstract

A novel fractal based circularly polarized GPS antenna is designed to meet the bandwidth requirements of satellite receiver (30 Abstract MHz) operating at a frequency of 1.575GHz. To achieve the circular polarization a truncated corner square patch technique is adopted. A 3-dBbased axial-ratio of 2.3405dB obtained at the gain obtained is 0.3694 A novel fractal circularly polarizedisGPS antenna is operating designed frequency. to meet theThe bandwidth requirements of dB. satellite receiver (30 MHz) operating at a frequency of 1.575GHz. To achieve the circular polarization a truncated corner square patch technique is adopted. A 3-dB axial-ratio of 2.3405dB is obtained at the operating frequency. The gain obtained is 0.3694 dB. © 2018 The Authors. Published by Elsevier B.V. © 2018 The Authors. by Elsevier B.V. This is an open accessPublished article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection andAuthors. peer-review underbyresponsibility © 2018 The Published Elsevier B.V.of the scientific committee of the 8th International Conference on Advances in Selection and peer-review under responsibility of the scientific committee of the 8th International Conference on Advances in Computing and access Communication (ICACC-2018). This is an open article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Computing and Communication (ICACC-2018). Selection and peer-review under responsibility of the scientific committee of the 8th International Conference on Advances in Keywords: Fractal; Circular polarization(CP); Truncated corner square patch ; ComputingMinkowski and Communication (ICACC-2018). Keywords: Minkowski Fractal; Circular polarization(CP); Truncated corner square patch ;

1. Introduction

1. Introduction GPS antennas provide an interface between satellites and the ground station which has been widely used for location information and tracking. To get reliable and uninterrupted communication GPS antenna are required to GPS provide an interface between satellites and size, the ground station has been widely used for meet theantennas performance specifications under constraints of small less weight andwhich low power requirements. location andGPS tracking. Todesign get reliable and uninterrupted communication antenna are to Fractalinformation concepts for antenna have been considered because they have GPS self-similarity [1]required properties meet specifications under constraints of small less weight andlength low power with the the performance parent structure, space filling property [2] in a size, smaller electrical and requirements. multiband/wideband Fractal concepts for GPS antenna design can havebebeen considered because they self-similarity independent performance. Fractal geometries grouped into deterministic andhave random structures. [1] properties with the parent structure, space filling property [2] in a smaller electrical length and multiband/wideband independent performance. geometries can be grouped into deterministic and random structures. * Corresponding author.Fractal Tel.: +918778296982 E-mail address: [email protected] * Corresponding author. Tel.: +918778296982 E-mail address: [email protected] 1877-0509 © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection peer-review under responsibility of the scientific 1877-0509and © 2018 The Authors. Published by Elsevier B.V. committee of the 8th International Conference on Advances in Computing and Communication (ICACC-2018). This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 8th International Conference on Advances in Computing and Communication (ICACC-2018). 1877-0509 © 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/) Selection and peer-review under responsibility of the scientific committee of the 8th International Conference on Advances in Computing and Communication (ICACC-2018). 10.1016/j.procs.2018.10.352

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Typical examples of deterministic types are Koch curve, Koch snowflake, Sierpinsky gasket, Minkowski loop [34], where each one offers different advantages such as multiband, circular polarization and improvement in performance characteristics. Natural phenomenon like dendrites and lightning bolts are the typical examples for random fractal geometries[5]. GPS antenna features such as circular polarization (CP), radiation efficiency, and directivity are the important parameters to be investigated during antenna design. A trade of between these parameters has to be validated with minimum size. The GPS signals are right hand circularly polarized (RHCP), after reflection they will convert to left hand circularly polarized. Thus, the use of circularly polarized antennas at the receiver can suppress the reflected signals. Planar circularly polarized fractal antennas have been proposed in literature for WLAN applications because of their compact dimension [6]. A novel design based on modification of Koch fractal geometry has been designed for circular polarization in square radiator by creating two asymmetric Koch fractal geometries on x-and y-planes of the single-probe feed [7]. A Defected Ground Structure (DGS) is designed by combining with fractal theory for improving parameters like bandwidth, cross polarization and gain in [8-9]. For GPS application a circular patch cross over has been presented in [10]. A MIMO antenna with two radiating elements has been reported in [11] for better isolation performance. This paper proposes the design of a circularly polarized fractal antenna for GPS system using a tailored and optimized Minkowski structure to meet the GPS antenna requirements within the size and volume constraints. Truncated corner square patches are used to obtain circular polarization requirement. Section 2 describes the design of the geometry and section 3 describes the optimization performance of the proposed antenna. In section 4 the simulated results are explained in detailed to understand the antenna performance. Section 5 gives the conclusion of the work. 2. Geometry of Proposed Fractal Antenna Minkowski loops are typically used to reduce the size of the antenna. In this work, the design of the antenna is evolved from a patch of length ’L’ and width ‘W’. The Minkowski curve fractal geometry [2-3] is introduced at the lower edge of the square patch. In the Minkowski island curve, we consider an initiator as a straight line having length ’l’. The line is divided into three equal parts of length (l / 3) and the middle segment is further replaced by two vertical and a horizontal segment of equal lengths (l / 3). This is known as the first iterated version of geometry. It is called generator and for the future iterations we divide the generator repeatedly using the following steps. The initiator and generator geometry are shown in Fig. 1.

Fig. 1: Minkowski curve fractal geometry

In the second iteration each segment of the generator is further divided into three equal parts of length (l / 9) and the middle segment is replaced by two vertical segments of length l / 18 and a horizontal segment of length l/ 9. In

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the third iterated Minkowski fractal structure, step 2 is applied at the lower edge of the square patch as shown in Fig. 2. Coaxial feeding technique is used to feed the antenna for impedance matching. To generate circular polarization, two electric field components of equal magnitudes with 90 degree phase difference are required. Here the concept of truncated corner patch is introduced to obtain circular polarization [12]. The top two corners of the patch are truncated and the two corner segments are separated from the patch by a narrow slot. The length of the corner square portion L2 is made larger than L3. The corner square segments have a dimension of L2×L2 mm2. 3. Optimized Performance of the Proposed Fractal Antenna FR4 epoxy material is used as antenna substrate with relative permittivity of 4.4, and thickness of 1.6 mm. The patch and ground are etched at the top and bottom of the substrate respectively. The patch dimensions are calculated

Fig. 2: Geometry of the proposed antenna

Fig. 3: Geometry of the proposed antenna with truncated corner square patch

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using length and width equations of microstrip patch antenna [13]. A fractal antenna with Minkowski fractal structure is designed and optimizations are carried out by using the commercial software High Frequency Structure Simulator (HFSS). From the optimization L2 is chosen as 6.2 mm and the slot is chosen as 0.5mm. The antenna structure with truncated corner square patch is shown in Fig. 3. The optimized dimensions of the antenna are given in Table 1. The x and y position of the probe feed is finalized at (-10, -10) location. Table 1. Optimized dimensions of the antenna Parameter

L

L1

L2

L3

W

W1

W2

Size (mm)

55

27.5

6.2

5

55

45

6.2

4. Simulation Results and Discussion 4.1. |S11| (dB)

The reflection coefficient S11 (dB) characteristics of three antennas are shown in Fig. 4. Antenna 1 is the square patch antenna with dimension L × L ×h mm3. Antenna 2 is the proposed fractal antenna without truncated corner patch and Antenna 3 is with truncated corner patch. The S11 value for Antenna 1 without truncation is obtained as -26.3710 dB at 1.63 GHz. For Antenna 2 with the fractal antenna the resonating frequency is shifted to 1.58 GHz to match the required operating GPS frequency with S11 value of -21.3803 dB. With the truncated corner square patch, the resonating frequency is found to remain at 1.58 GHz, however with reduced S 11 value of -12.5 dB. However, this still is within the limits of desired design specifications. The simulated and measured S11 values of the proposed antenna with truncated corner square patches are shown in Fig. 5. While simulation the resonating frequency was obtained as 1.58 GHz, but during measurement the resonating frequency shifted to 1.616 GHz due to the losses in SMA connector. The measurement setup for S11 is shown in Fig. 6.

0 -5

S11(dB)

-10 -15 -20 -25 -30 1.0

Square patch antenna Proposed antennawithout truncated square patch Proposed antenna with truncated square patch

1.2

1.4

1.6

Frequency(GHz) Fig. 4: S11(dB) curve of the antenna

1.8

2.0

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Fig. 5: Simulated and measured S11(dB) curve of the proposed antenna

Fig. 6: |S 11| Measurement setup for the proposed antenna

4.2. Axial Ratio Results

The corner segments provide perturbation to generate CP. The simulated axial ratio results of proposed antenna with and without the truncated corner patch as shown in Fig. 7. The axial ratio obtained without the truncated corner square patch is 32.4127 dB, which indicates that the antenna is not circularly polarized. With the truncated corner square patches at the top corners of the antenna the axial ratio has become 2.3405 dB which indicates circular polarization. Axial Ratio less than 3 dB is required to obtain circular polarization. From the simulation results it is evident that the axial ratio value is less than 3 dB when the truncated corner patch is introduced in the antenna which indicates the polarization is circular. The axial ratio measurement was carried out and the measurement result is shown in Fig. 8.

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Fig. 7: Simulated Axial Ratio value versus Theta (deg) of the proposed antenna at 1.575 GHz (a) without truncated corner square patch (b) with truncated corner square patch.

Fig. 8: Measured AxialRatio

4.3. Surface Current Distribution at 1.575 GHz (with truncated corner patch) The simulated surface current distribution of the proposed antenna with the truncated corner patch is as shown in Fig. 9. The truncated patch provides the required perturbation to generate circular polarization.

Fig. 9: Simulated surface current distributions of the proposed antenna with truncated corner patch (a) Phase=0deg (b) Phase=90deg (c) Phase=180deg (d) Phase=270deg

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4.4. Simulated Radiation Pattern The co-polarization and cross-polarization patterns of the antenna are given in Fig. 10. The GPS signals are right hand circularly polarized. The RHCP gain is 0.3694 dB in E and H plane of the antenna and the LHCP gain is -18.8326 dB. The summary of the simulated results for the proposed antenna without (Antenna 2) and with (Antenna 3) the truncated corner square patch is given in the Table 2.

Fig. 10: Simulated radiation pattern (a) E-plane (b) H-plane Table 2: Simulated results of proposed antenna

Antenna2 Antenna3

Resonating Frequency(GHz) 1.58

Return loss(dB)

Axial Ratio(dB)

-21.3803

32.4127

1.58

-12.5195

2.3405

5. Conclusion A novel fractal antenna with tailored Minkowski fractal geometry at GPS frequency is designed, optimized and simulated. With the fractal structure the antenna size is reduced. Circular polarization is obtained with the use of truncated corner square patch. An axial ratio of 2.3405 dB is obtained at the resonating frequency. Gain of 0.3694dB is obtained. 6. References [1] Singh, M., Sharma, N., (2016). “Comparison of multi-fractal antenna with star shaped fractal antenna for wireless applications” International Journal of Computer Applications (0975–8887) Volume. [2] Sinha, S. N., Jain, M., (2007). “A self-affine fractal multiband antenna”. IEEE Antennas and Wireless Propagation Letters 6, 110–112. [3] Tiwari, A., Rattan, M., Gupta, I., (2014). “Review on: Fractal antenna design geometries and its applications”. International Journal of Engineering and Computer Science 3 (09). [4] Khanna, G., Sharma, N., (2016). “Fractal antenna geometries: A review”. International Journal of Computer Applications 153 (7). [5] Poonam, S., Jadhav, M.M., (2016). “Review on Fractal Antennas for Wireless Communication”. International Journal of latest Trends in Engineering and Technology (IJLTET), Volume 6, Issue 3. [6] Pakkathillam, J. K., Kanagasabai, M., (2015). “Circularly polarized broadband antenna deploying fractal slot geometry”. IEEE Antennas and Wireless Propagation Letters 14, 1286–1289. [7] Farswan, A., Gautam, A. K., Kanaujia, B. K., Rambabu, K., (2016). “Design of koch fractal circularly polarized antenna for handheld UHF RFID reader applications”. IEEE Transactions on antennas and propagation 64 (2), 771–775. [8] Wei, K., Li, J., Wang, L., Xu, R., Xing, Z., (2017). “A new technique to design circularly polarized microstrip antenna by fractal defected ground structure”. IEEE Transactions on Antennas and Propagation 65 (7), 3721–3725. [9] Prajapati, P., Kartikeyan, M., Murthy, G., and Patnaik, A., (2015). “Design and testing of a compact circularly polarised microstrip antenna with fractal defected ground structure for L-band applications”, IET Microwaves, Antennas and Propagation, Vol. 9. [10] Jayakrishnan, V. M., Sreedevi, K. M., (2017). “Circular Microstrip Patch Assisted Planar Crossover for GPS Application”, Progress In Electromagnetics Research Symposium — Spring (PIERS), St Petersburg, Russia, 22–25 May. [11] Prakash, J., Vijay, R., Natarajamani, S., (2017). “MIMO antenna for mobile terminals with enhanced isolation in LTE band”. In: Advances in Computing, Communications and Informatics (ICACCI), 2017 International Conference on. IEEE, pp. 2231–2234. [12] Rahman, M. A., Nishiyama, E., Toyoda, I., (2017). “A frequency diversity reconfigurable antenna with circular polarization switching

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capability”. In: Antennas and Propagation & USNC/URSI National Radio Science Meeting, 2017 IEEE International Symposium on. IEEE, pp. 1367–1368. [13] Garg, R., Microstrip antenna design handbook. Boston, MA: Artech House, 2001.