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Note for Advanced Digital Signal Processing - ADSP by Sanaullah Khan

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Arun & Marx : Internet of Things Controlled Reconfigurable Antenna for RF Harvesting second ring is 22 mm and 26 mm, respectively. Both the rings are connected in the upper side with a square patch of 4 mm × 4 mm. The antenna ground is taken to be 50 mm × 50 mm to allow radiation above and below the substrate is described in the Table 1. Table 1. Details of length and width of the antenna Ring antenna (Parameters) Dimension (mm) Patch length 50 Patch width 50 Outer ring diameter 38 Inner ring diameter 26 Centre patch diameter 10 Feed length 11 Feed width 4 Ground plane length 50 Ground plane width 50 FR4 Substrate thickness 1.6 The prototype model testing is made with Vector Network Analyser (VNA) of 0 - 18 GHz. The equivalent circuit of the ring antenna will consist of lumped values of ground, PIN diode and radiating element of ring patch structure. This combined element of ring shaped antenna consists of parallel and series combination of RLC elements. At ON state of this antenna’s reconfigurable switching process the capacitance of respective PIN diodes (D1, D2) are getting cancelled. 3. IoT SWITCHING Switching for this antenna is provided by PIN Diode which is controlled by NodeMCU unit as like the micro-controller switching device3. The block diagram for IoT based switching of Ring Antenna with the help of PIN Diode switches is shown in the Fig. 3. The NodeMCU switches the Diodes D1 and D2 as per the software programmed in it. The Biasing voltage from the NodeMCU can switch on and off the D1 and D2 PIN diodes. Based on the diode switching of The antenna is designed with the help of circular patch antenna dimension equation as follows12. a= F= F 1  2h   Π F    2 ln  1 +  + 1.7726   Πε F   2h     r  8.791*109 f r ε (1) (2) r where a is area of the ring structure and F is antenna frequency. The substrate FR4 thickness and relative permitivity is denoted as h and ε correspondingly. After r including the fringing effect of the circular patch antenna, the effective radius (ae) of the patch antenna is derived from the Eqn. (3) as follows, 1    2 2h   Π a  a = 1 + ln   + 1.7726   e Πε a   2h     r (3) With the assistance of Eqn. (3) the resonant frequency (fr) of the antenna is derived as per the Eqn. (4) 1.8412ν 0 (4) = f r 110 2Πa ε e r ( ) (b) (a) Figure 1. Antenna layout: (a) Top view and (b) Bottom view (all dimensions are in mm). (a) (b) Figure 2. Prototype design of ring antenna with PIN diodes D1 and D2 (a) Front view (b) Back view. The outer ring patch is connected to the inner ring patch with PIN diode D1 and the inner ring is in contact with the center circular patch with PIN Diode D2. Here in this proposed work SOD323 PIN diodes are used, which provides switching to the reconfigurable antenna. The antenna is simulated using HFSS simulator tool and the switching is provided using Lumped RLC boundary. The detail layout structure of antenna is as shown in the Fig. 1. Figure 3. Block diagram of IoT based reconfigurable ring antenna. 567

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Def. SCI. J., Vol. 68, No. 6, november 2018 ON and OFF, the flow of RF signal through the Ring Antenna is varied and the different band of operating frequencies can be achieved. The NodeMCU unit itself consists of WiFi based connectivity with the Internet. This combined reconfigurable antenna and NodeMCU unit control, change of program and monitor through World Wide Web. The prototype model of PIN diode embedded Reconfigurable Ring shaped antenna is connected with the IoT device (NodeMCU) is as shown in above Fig. 4. Frequency (GHz) (a) Figure 4. IoT device connected with the ring antenna. 4. RESULTS AND DISCUSSION The proposed IoT-based reconfigurable antenna is designed and validated using HFSS software. In the experimental measurement PIN diodes used as a switching element and the Prototype antenna results are obtained with VNA. When the D1 and D2 is in off state the antenna operates in the frequency band of 2 GHz to 5 GHz and suitably providing peak response (fp) in 4.5 GHz frequency range, this is considered as a state ‘0’ of the antenna and the results are as shown in the Fig. 5(a). In the state ‘1’, the D1 is in on condition while the D2 is remains off condition, and the obtained frequency range of 2 GHz to 3.7 GHz and concentrates on 3.5 GHz band is as shown in Fig. 5(b). As shown in the Fig. 6(a) the return loss results for stage 3, where the diodes D1 and D2 is in OFF and ON conditions respectively. Here in this state the operating frequency ranges from 1.8 GHz to 3.4 GHz, and it focuses the 2.4 GHz Band. In state 4 both the diodes are in ON condition and the results as shown in Fig. 6(b). In this state the frequency ranges from 1 GHz to 3.7 GHz and it concentrates on the 1.8 GHz band. There is a discrepancy between simulated and measurement results due to switch installation and measuring environment. The comparison table for the four switching states diode’s condition, its working/ resonant frequency range and bandwidth for the appropriate states of the antenna is as given in Table 2. The radiation pattern in E-plane (i.e. X-Z plane represented in brown colour) and the radiation pattern in H-plane (i.e. Y-Z plane represented in red colour) at 2.4 GHz in OFF state and 3.2 GHz and 4.5 GHz in ON state is revealed in the Figs. 7(a), 7(b) and 7(c). The radiation pattern remains same for all the 568 Frequency (GHz) (b) Figure 5. Measured and simulated return loss: (a) state 1 and (b) state 2. Frequency (GHz) (a) Frequency (GHz) (b) Figure 6. Measured and simulated return loss: (a) state 3 and (b) state 4.

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Arun & Marx : Internet of Things Controlled Reconfigurable Antenna for RF Harvesting (a) (c) (b) Figure 7. Radiation pattern: (a) state 1, (b) state 3, and (c) state 4. Table 2. Comparison of Four switching states 0, 0 (state 1) OFF OFF 2-5 (fp = 4.5) 3 0, 1 (state 2) OFF ON 2 - 3.7 (fp = 3.5) 1.7 1, 0 (state 3) ON OFF 1.8 - 3.4 (fp = 2.4) 1.6 1, 1 (state 4) ON ON 1 - 3.7 (fp = 1.8) 2.7 gain (dB) Antenna PIN Diode Working/ resonant Bandwidth switching states D1 frequency (GHz) (GHz) D2 reconfigured frequencies and bidirectional radiation pattern is obtained in the all switching states of antenna. The following Fig. 8 shows the cumulative gain plot of the proposed antenna’s four switching states. It is inferred that the antenna presents a positive gain in operating frequency bands all the states. In state 1, the maximum gain of 2.5 dB is obtained at the frequency of 4.5 GHz. Similarly, in the state 2 and state 3, a gain of 2.7 dB and 1.9 dB is obtained at 3.5 GHz and 2.4 GHz, respectively. Where, in 4th state a peak gain of 1.6 dB at 1.8 GHz and a moderate gain of 0.7 dB at 3.5 GHz is obtained. The obtained gain values for the four switching states of the antenna are as given in Table 3. Where, the Fig. 9 shows the current distribution in antenna switching from state 1 to state 4. In switching state 3 (D1-ON; D2-OFF), the majority of the current flow is distributed in the lower side of the circular ring patch antenna. In state 4 (D1-ON; D2-ON) the current in concentrated both in the outer and inner ring of the antenna. Table 3. Maximum gain obtained at each switching state Switching states Peak gain State 1 2.5 dB at 4.5 GHz State 2 2.7 dB at 3.5 GHz State 3 1.9 dB at 2.4 GHz State 4 1.6 dB at 1.8 GHz Due to the variation in current distribution different frequency reconfiguration is obtained. Frequency (GHz) Figure 8. Measured gain plot of the antenna. Figure 9. Current distribution :(a) state 1,(b) state 2,(c) state 3, and (d) state 4. 5. RF ENERGY HARVESTING This Novel experimental setup is made as shown in the Fig. 10 (a) to scavenge the various ranges of ambient RF energy and can act as a permanent energy harvesting resource for the low power VLSI devices. Compared to the existing harvesting technologies, this 569

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Def. SCI. J., Vol. 68, No. 6, november 2018 (a) (b) Figure 10. RF energy harvesting module: (a) Block diagram of IoT based reconfigurable ring antenna and (b) Testing setup. proposed IOT controlled reconfigurable antenna module tunes to the appropriate frequency band available in that zone. The complete module has been fixed and tested in the open area of a building terrace in the range of 25 m away from the mobile phone tower (GSM 1800) is shown in Fig. 10 (b). With the help of DC to DC booster (LTC3105) circuit, the harvested energy from the antenna is rectified and boosted. Finally, a constant 5 V output is obtained from this embedded module. 6. CONCLUSIONs This novel frequency reconfigurable ring antenna with IoT based controlled switch for wireless communication is presented. The importance of these techniques is that the total reconfigurable antenna setup is monitored and controlled from the remote in anywhere worldwide. The switching provided by NodeMCU with PIN diodes (SOD323) has high isolation and also high voltage interference with antenna radiation is eliminated. Switching bands of 4.5 GHz, 3.5 GHz, 2.4 GHz and 1.8 GHz are attained in each states of 1st, 2nd, 3rd and 4th state respectively. This prototype reached a maximum gain of 2.7 dB in 3.5 GHz, 2.5 dB in 4.5 GHz, 1.9 dB in 2.4 GHz, and 1.6 dB in 1.8 GHz. Bidirectional radiation pattern is attained in all condition and shows a positive gain response throughout its operating frequency band. This reconfigurable antenna can work on different wireless standards like GSM 1800, DCS 1900, ISM Band, Wi-Fi, Bluetooth, 4G (LTE), Wi-Max, WLAN and some of Satellite Frequency bands. A constant 5 v is obtained with the RF harvesting module in 1800 MHz band. 570 REFERENCES 1. Shah, S.A.A.; Khan, M.F. ; Ullah, S. & Flint, J.A. Design of a multi-band frequency reconfigurable planar monopole antenna using truncated ground plane for Wi-Fi, WLAN and WiMAX applications. In IEEE International Conference on Open Source Systems and Technologies (ICOSST), 2014, pp. 151-155. doi: 10.1109/ICOSST.2014.7029336 2. Sulakshana, Chilukuri & Lokam Anjaneyulu. Reconfigurable antennas with frequency, polarization, and pattern diversities for multi-radio wireless applications. Int. J. Microwave Wireless Technol., 2017, 9(1), 121132. doi: 10.1017/S1759078715000926 3. Zhang, Jian; Yang, Xue-Song; Li, Jia-Lin & Wang, Bing-Zhong. Triangular patch yagi antenna with reconfigurable pattern characteristics. App. Computational Electromagnetics Soc. J., 2012, 27(11), 918-924. 4. Costantine, Joseph; Youssef, Tawkb & Christos, G. Christodoulouc. Reconfigurable antennas and their applications. In Handbook of Antenna Technologies, Springer, Singapore, 2015. pp. 1-30. doi: 10.1007/978-981-4560-75-7_61-1 5. Arun, V. & Karl Marx, L.R. Micro-controlled tree shaped reconfigurable patch antenna with RF-energy harvesting.  Wireless Personal Commun.,  2017, 94(4), 2769-2781. doi: 10.1007/s11277-017-3975-z 6. Yang, Xiaofan; Yao, Chen; Longfang, Ye; Manxi, Wang; Min, Yu & Qing, Huo Liu. Frequency reconfigurable circular patch antenna using PIN diodes. In  IEEE International Conference on Microwave and Millimeter Wave Technology (ICMMT), 2016, 2, pp. 606-608. doi: 10.1109/ICMMT.2016.7762382 7. Onodera, Shoichi; Ryo, Ishikawa; Akira, Saitou & Kazuhiko, Honjo. Multi-band reconfigurable antennas embedded with lumped-element passive components and varactors. In  IEEE Microwave Conference Proceedings (APMC), 2013 Asia-Pacific, pp. 137-139. doi: 10.1109/APMC.2013.6695216 8. Christodoulou, Christos G.; Youssef Tawk; Steven A. Lane & Scott R. Erwin. Reconfigurable antennas for wireless and space applications. In  Proceedings of the IEEE, 100(7), pp. 2250-2261. doi: 10.1109/JPROC.2012.2188249 9. Genovesi; Simone; Agostino, Monorchio; Michele, Borgese Borgese; Sara, Pisu, & Fabio, Michele Valeri. Frequency-reconfigurable microstrip antenna with biasing network driven by a PIC microcontroller. IEEE Antennas Wireless Propag. Lett., 2012, 11, 156-159. doi: 10.1109/LAWP.2012.2185673 10. Pal, Heena & Choukiker, Yogesh Kumar. Design of frequency reconfigurable antenna with ambient RFenergy harvester system. In International Conference On Information Communication and Embedded System (ICICES2016), India, 2016, 2(1), 1-5. doi: 10.1109/ICICES.2016.7518857 11. Sun, Hucheng; Yong-xin, Guo; Miao, He & Zheng, Zhong.

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