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  • 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 188 TRIANGULAR SLOT CIRCULAR PATCH ANTENNA FOR CIRCULAR POLARIZATION RECONFIGURABILITY Uma Shankar Modani1 , Anubhav Kanwaria2 1 (Govt. Engg. College, Ajmer, Rajasthan, India) 2 (Govt. Engg. College, Ajmer, Rajasthan, India) ABSTRACT This paper proposes a reconfigurable microstrip patch antenna with polarization states being switched between left hand circular polarization (LHCP) and right hand circular polarization (RHCP). The CP mode has been excited by perturbation element which is a triangular slot in the circular patch. Two PIN diodes are symmetrically placed on each side of triangular slot to alter the current direction around the patch, which determines the polarization state. By changing the state of the PIN diode, the antenna has been made to switch between twp states of circular polarization. This polarization reconfigurable patch antenna covers IEEE 802.11 outdoor band and has good agile polarization performance with nearly 48MHz CP bandwidth and minimum axial ratio near to 1dB. The minimum axial ratio frequency for LHCP and RHCP are same as 5.80GHz. Keywords: Axial ratio, Circular polarization, Microstrip antenna, Reconfigurable antenna. 1. INTRODUCTION RECONFIGURABLE antennas play an important role in modern wireless communication systems, such as personal communications service (PCS) and wireless local area network (WLAN). Reconfigurability may be present in resonant frequency, radiation pattern and/or polarization state [1– 4]. Reconfigurable antennas with polarization diversity can realize frequency reuse, which expands the capability of communication systems, and are useful when the operating frequency band is limited [5, 6]. In addition, since a polarization diversity antennas can also alleviate the harmful influence caused by multipath effects [7], therefore a polarization control is required from linearly polarized to circularly polarized or a right-handed CP (RHCP) to a left-handed CP (LHCP) or vice versa. Circular polarized microstrip patch antenna using dual feed which symmetrically excite two orthogonal modes with 90 degree phase difference, needs a complicated feeding network [8– 10] therefore single feed circularly polarized antennas are currently receiving much attention, because it allows a reduction in the complexity, weight and the RF loss of any antenna feed and is desirable in situations where it is difficult to accommodate dual orthogonal feeds with a power divider network INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August, 2013, pp. 188-197 © IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2013): 5.8896 (Calculated by GISI) www.jifactor.com IJECET © I A E M E
  • 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 189 [11, 12]. The patch with a single point feed detunes degenerate modes of a symmetrical patch by perturbation segments. Many, electrically controllable antennas have been researched with switchable circularly polarization using perturbation technology such as switching slots [13– 16], switching feeding point [17–20], and a switching corner truncations [21–23]. In this paper, a single feed reconfigurable microstrip patch antenna with an annular triangular shaped slot has been proposed. The antenna has a simple configuration on a planar substrate. 2. ANTENNA DESIGN Fig. 1 shows the geometry of the proposed single-fed circular microstrip patch antenna with an annular triangular slot. The antenna consists of an inner equilateral triangle and outer circular patch on Roger 5880 substrate with the thickness of 1.6mm and a relative dielectric constant of 2.2. These two patches are connected by two pin diodes which are symmetrically placed with opposite polarities at a point P which is 10.5mm apart from the top vertex of inner triangular patch along the gap. Fig. 1 Geometry of proposed antenna The feeding point of the antenna is located at F which is 17.5mm apart from the center of the patch on the negative X axis. Table I Dimensions of the Radiating Patch Geometry Parameters Dimensions (mm) R(radius) 47.0 S(side) 43.2 P(position o f diode) 10.5(from top vertex) G(gap) 1.0 Ground size 110 × 110
  • 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 190 Fig. 2 shows the configurations of the prototype antenna. For the simulation purpose, the ON condition of PIN diode has been realized by the presence of conductor and OFF condition of the diode has been realized by the absence of conductor. In this way, the diode is assumed as ideal. The design process involves resonating inner equilateral triangle near to 5.80GHz band and then optimizing parameter mentioned in TABLE I for better results which include good matching, nearly same minimum axial ratio point for LHCP and RHCP mode, and better gain performance. (a) (b) Fig. 2 Geometry of the simulated prototype antenna: (a) LHCP mode. (b) RHCP mode The antenna polarization is controlled by switching the bias voltage between the triangular patch and the outer circular patch. As the Diode D1 off and D2 is ON, the antenna has LHCP mode and when Diode D2 off and D1 is ON, the antenna presents RHCP mode. The proposed antenna is simulated with the aid of Ansoft HFSS software. The simulated return loss and axial ratio plot of the proposed antenna have been shown in Fig. 3 and associated results are shown in TABLE II. 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 Freq [GHz] -30.00 -25.00 -20.00 -15.00 -10.00 -5.00 0.00 ReturnLoss(dB) RETURN LOSS m1 m2 Curve Info LHCP RHCP Name X Y m1 5.8025 -25.7164 m2 5.8025 -24.7289 (a)
  • 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 191 5.76 5.78 5.79 5.79 5.80 5.82 5.83 Freq [GHz] 0.50 1.00 1.50 2.00 2.50 3.00 3.50 AxialRatio(dB) AXIAL PLOT m1 m2 Curve Info LHCP RHCP Name X Y m1 5.8000 0.8680 m2 5.8000 1.0294 (b) Fig. 3 Rectangular plot (a) Return loss plot for LHCP and RHCP mode (b) Axial ratio plot for LHCP and RHCP mode TABLE III: RESULTS OF DESIGN ANTENNNA IN TWO MODES Parameters Return Loss (dB) Impedance BW (MHz/%) FL(GHz) FU(GHz) LHCP 5.802GHz -25.71 541/9.32% 5.442 5.983 RHCP 5.802GHz -24.72 533/9.23% 5.444 5.977 The design exhibits circular polarization reconfigurability around 5.80GHz resonant bands for nearly 48MHz bandwidth. Minimum axial ratio for LHCP mode is .868dB at 5.80GHz with total gain of 2.058dB while for RHCP mode minimum axial ratio is 1.029dB at 5.80GHz with total gain 1.774dB as shown in Fig. 3 and Fig. 4. It has also been shown in Fig. 4 that the total gain radiation patterns are having almost same shape for both the modes. 0.00 2.00 4.00 6.00 90 60 30 0 -30 -60 -90 -120 -150 -180 150 120 Radiation Pattern 4 m1 Curve Info Gain Total (dB) Name Ang Mag m1 0.0000 2.0580 (a)
  • 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 192 0.00 2.00 4.00 6.00 90 60 30 0 -30 -60 -90 -120 -150 -180 150 120 gain plot m1 Curve Info Gain Plot (dB) Name Ang Mag m1 0.0000 1.7745 (b) Fig. 4 Total gain radiation pattern (dB) at Minimum axial ratio point, 5.80GHz, for E plane (a) LHCP mode (b) RHCP mode Around polarization band and at minimum axial ratio point, the polarization ratio radiation pattern plot has been shown for both the modes in Fig. 5, which indicates that the proposed antenna is left hand circularly polarized (LHCP) in most part of the curve for LHCP mode and right hand circularly polarized in most part of the curve for RHCP mode. -18.00 -6.00 6.00 18.00 90 60 30 0 -30 -60 -90 -120 -150 -180 150 120 Pr LHCP Curve Info PR LHCP (dB) PR RHCP (dB) (a) -18.00 -6.00 6.00 18.00 90 60 30 0 -30 -60 -90 -120 -150 -180 150 120 gain plot1 Curve Info PR RHCP (dB) PR LHCP (DB) (b) Fig. 5 Polarization ratio radiation pattern for E plane at 5.80GHz (a) LHCP mode (b) RHCP mode
  • 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 193 The proposed antenna possesses positive gain at all planes in both the modes when theta (Ѳ) is 0 degree for desired polarization reconfigurable band extending from 5.770GHz to 5.882GHz and high gain is observed when ‘Ѳ’ is around 40 degree as shown in Fig. 6. 5.72 5.74 5.76 5.78 5.80 5.82 5.84 5.86 5.88 Freq [GHz] 1.70 1.80 1.90 2.00 2.10 2.20 2.30 2.40 2.50 2.60 TotalGain(dB) gain plot thetazero m1 m2 Curve Info LHCP RHCP Name X Y m1 5.8025 2.0534 m2 5.8025 1.7646 (a) 5.72 5.74 5.76 5.78 5.80 5.82 5.84 5.86 Freq [GHz] 6.15 6.20 6.25 6.30 6.35 6.40 6.45 6.50 6.55 TotalGain(dB) gain plot thetazero 40 m1 m2 Curve Info LHCP RHCP Name X Y m1 5.8025 6.3190 m2 5.8025 6.4888 (b) Fig. 6 Total gain rectangular plot (a) Ѳ is 0 degree (b) Ѳ is 40 degree 3. STUDY OF VARIOUS PARAMETERS OF PROPOSED ANTENNA DESIGN In this section, the antenna design parameters are varied and the effects of these variations on the return loss and axial ratio of the antenna have been observed. For this study, the antenna design shown in Fig. 2(a) has been used. Return loss curve has shown four resonating bands with third band being the main resonant mode. Their matching is tightly controlled by feed position, position of diode and outer circular patch radius which directly affects -10dB bandwidth also. It has been observed that as feed moves along negative X axis, lower band matching increases and higher band matching reduces. The affect of other parameters, varying one and keeping other constant have been studied. 3.1 Variation In The Position Of Diode (P) The position ‘P’ has been varied keeping all other parameters same as shown in Table I and the results of return loss plots and axial plots for three values have been shown in Fig. 7. As diode position move farther from top vertex of inner equilateral triangle, the matching of first and third
  • 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 194 band increases while the second and fourth band matching disturbs, therefore bandwidth decreases. Reverse effect has been observed when diode position P is decreased. It has been shown that P at 10.5mm distance offers best trade off, between AR bandwidth and minimum axial ratio. Also, minimum axial ratio point at P of 9.5mm is same for both the modes. 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 Freq [GHz] -30.00 -25.00 -20.00 -15.00 -10.00 -5.00 0.00 ReturnLoss(dB) RETURN LOSS m1 m2 m3 Name X Y m1 5.7850 -19.6816 m2 5.8025 -25.7164 m3 5.7675 -22.2229 Curve Info P 9.5 mm P 10.5 mm P 11.5 mm (a) 5.72 5.74 5.76 5.78 5.80 5.82 5.84 Freq [GHz] 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 AxialRatio(dB) AXIAL PLOT m1 m2 m3 Curve Info P 9.5 mm P 10.5 mm P 11.5 mm Name X Y m1 5.7675 1.4360 m2 5.8000 0.8680 m3 5.8150 0.8270 (b) Fig. 7 Rectangular plot for variation in position of diode (P) (a) Return loss plot (b) Axial ratio plot 3.2 Variation In Radius Of Circular Patch (R) The Radius ‘R’ has been varied keeping all other parameters same as shown in Table I and the result of return loss plots and axial plots for three values have been shown in Fig. 8. Parameter R affect design antenna attributes opposite to P parameter. As radius increases higher band matching increases and lower band matching disturbs as shown in Fig.8 (a). In contrast to parameter P, patch radius greatly affects minimum axial ratio value with leftwards movement of axial ratio band. Minimum axial ratio value improvement from 1.28dB to 0.46dB has been observed as patch radius varies from 46.5mm to 47.5mm as shown in Fig. 8(b) but observed total gain at circularly polarized band also decreases to less than 1.50dB as shown in Fig. 9. Therefore, patch radii of 47mm has been chosen with the optimum gain and minimum axial ratio of 2.053dB and .868dB respectively. The other parameter such as peak directivity, peak gain and radiation efficiency are shown in TABLE III.
  • 8. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 195 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 Freq [GHz] -30.00 -25.00 -20.00 -15.00 -10.00 -5.00 0.00 ReturnLoss(dB) RETURN LOSS m1m2 m3 Name X Y m1 5.8200 -26.4596 m2 5.8025 -25.7164 m3 5.7850 -24.3543 Curve Info R 46.5 mm R 47.0 mm R 47.5 mm (a) 5.76 5.77 5.78 5.79 5.80 5.81 5.82 5.83 Freq [GHz] 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 AxialRatio(dB) AXIAL PLOT m1 m2 m3 Curve Info R 46.5 mm R 47 mm R 47.5 mm Name X Y m1 5.8050 1.2801 m2 5.8000 0.8680 m3 5.7850 0.4613 (b) Fig. 8 Rectangular plot for variation in radius of circular patch (R) (a) Return loss plot (b) Axial ratio plot 5.76 5.77 5.78 5.79 5.80 5.81 5.82 5.83 Freq [GHz] 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60 TotalGain(dB) gain plot thetazero1 Curve Info R 46.5 mm R 47 mm R 47.5 mm Fig. 9 Total gain rectangular plot for variation in radius of circular patch (R) at circular polarized band
  • 9. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 196 TABLE III: SIMULATED RESULTS OF ANTENNA PARAMETERS Parameters Peak Directivity Peak Gain Radiation Efficiency Mode Minimum axial ratio point LHCP 5.80GHz 5.907 5.889 99.68 RHCP 5.80GHz 6.097 6.093 99.94 4. CONCLUSION A single probe-fed polarization reconfigurable microstrip antenna with a triangular slot has been proposed for polarization diversities. It has been shown that the polarization of the proposed antenna can be controlled between left hand circular polarization and right hand circular polarization states by switching the PIN-diodes located near to the top vertex of equilateral triangular slot inside the main circular patch. The proposed simple polarization reconfigurable planar antenna can be applicable for WLAN communication terminals with polarization diversities. REFRENCES [1] Uma Shankar Modani, and Anubhav Kanwaria, “Frequency Reconfigurable Multiband Microstrip Patch Antenna for Various Wireless Services,” IEEE International Conference on Advanced Research in Engineering and Technology (ICARET), Publication year 2013, pp. 496-500. [2] G. Monti, L. Corchia, and L. Tarricone, “Planar Bowtie Antenna with A Reconfigurable Radiation Pattern,” Progress in Electromagnetic Research C, Vol. 28, 61-70, 2012. [3] Uma Shankar Modani, and Anubhav Kanwaria, “A Survey on Polarization Reconfigurable Patch Antennas,” International Journal of Recent Technology and Engineering (IJRTE), Vol. 1, Issue-6, pp. 126-129, Jan. 2013. [4] Uma Shankar Modani, and Anubhav Kanwaria, “Triangular Slot Circular Patch Antenna for Polarization Reconfigurability,” International Journal of Electronics and Communication and Technology (IJECET), Vol. 4, Issue-4, Aug. 2013, pp. 166-175. [5] K.-H. Chung, Y.-S. Nam, T.-Y. Yun, and J.-H. Choi, “Reconfigurable Microstrip Patch Antenna with Switchable Polarization,” ETRI Journal, Vol. 28, No. 3, pp. 379- 382, July 2006. [6] D. Jung, T. Fukusako, N. Kitamura, N. Mita, and C. Ha, “Polarization Switchable Microstrip Antenna Using PIN-diodes,” IEICE Trans. Comm., Vol.E87-B, No.1, pp.152-157, Jan. 2004. [7] R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon, : Microstrip antenna design handbook, Artech House, Norwood, May 1995. [8] W.B. Wei, Q.Z. Liu, Y. Z. Yin, and H. J. Zhou, “Reconfigurable Microstrip Patch Antenna with Switchable Polarization,” IEEE Transactions on Antennas and Propagation, Vol. 28, No. 11, 2010. [9] Eisuke Nishiyama, and Masayoshi Aikawa, “Circular Polarizations Switchable Microstrip Antenna with SPDT Switching Circuit,” Proceedings of the 36th European Microwave Conference, 2006. [10] Fabien Ferrero, Cyril Luxey, Robert Staraj, Gilles Jacquemod, Matthew Yedlin, and Vincent Fusco, “A Novel Quad-Polarization Agile Patch Antenna,” IEEE Transactions on Antennas and Propagation, Vol. 57, No. 5, May 2009.
  • 10. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME 197 [11] Ravindra Kumar Yadav, Jugul Kishor, and Ram. Lal Yadava, “Compensation of Dielectric Cover Effects on CP Hexagonal Microstrip Antenna,” IJECET Volume 4, Issue 1, pp. 43-54, January- February (2013). [12] Xue-Xia Yang, Bing-Cheng Shao, Fan Yang, Elsherbeni, and Bo Gong, “A Polarization Reconfigurable Patch Antenna with Loop Slots on the Ground Plane,” IEEE Antennas and Wireless Propagation Letters, Vol. 11, 2012. [13] Won-Sang Yoon, Sang-Min Han1, Seongmin Pyo, Jung-Woo Baik, and Young-Sik Kim, “A Polarization Switchable Microstrip Patch Antenna with a Circular Slot,” IEEE 978-1-4244- 2642-3-08-2008. [14] M. K. Fries, M. Gräni, and R. Vahldieck , “A Reconfigurable Slot Antenna with Switchable Polarization,” IEEE Microwave and Wireless Components Letters, Vol. 13, No. 11, pp. 490 - 492, Nov. 2003. [15] D.-H. Hyun, J.-W. Baik, S. H. Lee, Y.-S. Kim, “Reconfigurable Microstrip Antenna with Polarization Diversity,” Electronics Letters, Vol. 44, No. 8, pp. 509-510, Apr. 2008. [16] H. Aissat, L. Cirio, M. Grzeskowiak, J.-M. Laheurte, and O. Picon, “Reconfigurable Circularly Polarized Antenna for Short-Range Communication Systems,” IEEE Transactions on Microwave Theory and Techniques, Vol. 54, No. 6, pp. 2856-2863, Jun. 2006. [17] Chia-Luan Tang, Jui-Han Lu and Kin-Lu Wong, “Circularly Polarized Equilateral-Triangular Microstrip Antenna with Truncated Tip,” Electronics Letters Vol. 34 No. 13, 25th June 1998. [18] Pratibha Sekra, D. Bhatnagar, V.K. Saxena and J.S. Saini, “Single Feed Circularly Polarized Edge Truncated Elliptical Microstrip Antenna,” International Conference on Emerging Trends in Electronic and Photonic Devices & Systems (Electro), 2009. [19] Shing-Lung Steven Yang and Kwai-Man Luk, “A Wideband L-Probes Fed Circularly- Polarized Reconfigurable Microstrip Patch Antenna,” IEEE Transactions on Antennas and Propagation, Vol. 56, No. 2, February 2008. [20] N. Jin, F. Yang, and Y. Rahmat-samii, “A Novel Patch Antenna with Switchable Slot (PASS): Dual Frequency Operation with Reversed Circular Polarizations,” IEEE Transactions on Antennas and Propagation, Vol. 54, no. 3, pp. 1031-1034, Mar. 2006. [21] Y. J. Sung, T. U. Jang, and Y.-S. Kim, “A reconfigurable microstrip antenna for Switchable polarization,” IEEE Microwave and Wireless Components Letters, Vol. 14, No. 11, pp. 534- 536, Nov. 2004. [22] Kyungho Chung, Yongsik Nam, Taeyeoul Yun, and Jaehoon Choi, “Reconfigurable Microstrip patch Antenna with Frequency and Polarization-Diversity Functions,” Microwave And Optical Technology Letters, Vol. 47, No. 6, December 2005. [23] Kyungho Chung, Yongsik Nam, Taeyeoul Yun, and Jaehoon Choi, “Reconfigurable Microstrip Patch Antenna with Switchable Polarization,” ETRI Journal, Vol. 28, No. 3, June 2006. [24] Uma Shankar Modani and Gajanand Jagrawal, “A Slotted E-Shaped Stacked Layers Patch Antenna for 5.15-5.85 Ghz Frequency Band Applications”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 4, Issue 3, 2013, pp. 11 - 23, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472. [25] Uma Shankar Modani and Gajanand Jagrawal, “Microstrip Line Fed Stacked Layer E- Shaped Patch Antenna for Wlan and Wimax Applications”, International Journal of Electronics and Communication Engineering & Technology (IJECET), Volume 4, Issue 3, 2013, pp. 48 - 55, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.