A Design of Switched Beam Antenna For Wireless Sensor Networks

Transcription

1 Indian Journal of Engineering Research and Technology (IJERT) ISSN Volume 2, Number 1 (2015), pp. 1-8 GBS Publishers & Distributors (India) A Design of Switched Beam Antenna For Wireless Sensor Networks 1 Ms.M.Sujatha Faculty of ECE, Research Scholar, Sathyabama University & Associate Professor, Prathyusha Institute of Technology and Management, Chennai, 1 sujatha.ece@prathyusha.edu.in 2 Dr. R.S. Bhuvaneswaran Associate Professor, Annauniversity, 2 bhuvan@annauniv.edu 3 Mr. D.kaviyarasan Prathyusha Institute of Technology and Management,Chennai. Abstract Saving energy is the most important constraint in Wireless Sensor Network(WSN). This is mainly due to the battery's life time as it is inconvenient to replace the batteries. Hence the power transmission could be controlled and made in an efficient manner thus reducing the usage of battery. In order to achieve this, Switched beam antennas and WSN nodes are integrated which extends the sensor lifetime by optimizing power transmission. The switched beam antenna overcomes the disadvantage of omni directional antenna in the context of wastage of power. The proposed antenna consists of four arrays of two L-shaped quarterwavelength slot antenna elements arranged in a symmetrical planar structure. The array is replicated three times and rotated 90 degrees along the axis perpendicular to the x-axis and passing through the center of the circumference. The radiating structure is fed at the center of the antenna. The array of two L-shaped quarter-wavelength slot antenna elements exhibits a directional radiation pattern with the main lobe direction oriented as the bisector of the angle identified by the two antenna elements. Some arrays have been combined in order to have a uniform coverage of the 360 degrees in the azimuth plane. Simulations and experimental results, demonstrate the appropriateness of the proposed switched-beam antenna system as hardware element enabling new power saving strategies in WSN contexts. Keywords: Energy Efficiency, Switched beam antenna, Wireless Networks.

2 2 M.Sujatha, R.S. Bhuvaneswaran and D.kaviyarasan Introduction A mote is a WSN node which has several sensors to sense and collect information about the surrounding environment. It has a low power processor, a small memory to store data and a battery power supply. A radio frequency transceiver of 2.96 GHz, equipped with a proper antenna which is a simple dipole is used to perform data communication among motes. Energy efficiency is an important objective in WSN. Motes are usually placed in situations and places where it is very difficult to replace the batteries and it is a very time consuming process. The motes lifetime should be increased so as to reduce the maintenance and outages. The RF front end requires more power for data communication. The power required by the mote processor to perform thousand operations is equal to that needed by the RF transceiver to transmit a single bit. A technique to minimize the energy consumption is proposed in [1-2]. These techniques use specific protocols to optimize data transmission by periodically switching the mote into sleep mode or controlling the radio transceiver activation. To further increase the mote lifetime and energy efficiency opportunely controlled directional or switch beam antennas can be used. A new model with pattern reconfigurable antenna based on micro strip parasitic array elements is proposed in [3]. It is very simple and compact but it does not provide uniform coverage in all directions. This model occupies large volume and does not provide uniform pattern. To overcome this, a new model based on switched beam antenna composing of a four element array is proposed in [4]. It has one omnidirectional and eight switchable directional patterns and provides a uniform coverage of 360 degree horizon. It is very compact and inexpensive. Each single beam exhibits an HPBW of 120 which causes too large overlapping area for energy saving. To overcome this, a new model reconfigurable beam steering antenna is presented in [5]. It has eight micro strip antennas in a 3d configuration and a vertical half wavelength dipole antenna to provide nine radiation patterns. A digital control circuit is used to switch among nine radiation patterns which have an HPBW of nearly 60 degrees. It provides a uniform coverage of 360 but the main issue is it is very difficult to use with a WSN node due to its 3d configuration. A conventional L-slot antenna is described in [6-7]. The slot composed of two slots which are connected at their ends with 90 degree angle. The total slot length is equal to the quarter wavelength with the reference frequency. A 50 ohm micro strip feeding line is used to feed the antenna, which is suitable for integration with the electronic devices. The slot antenna acts as a small dipole antenna oriented along the y axis with a directional pattern in the azimuth plane. The L shaped antenna exhibits maximum gain in the maximum radiation direction and this will consume more power. A full planar and compact switched beam antenna in the ISM band is modeled for WSN applications. It replaces the omni-directional antenna and a digital interface is used to control the radiation properties. There are four radiating structures each with two L shaped elements and hence there are eight L shaped quarter wavelength slot antennas. These elements are arranged in a compact and symmetrical planar structure. There are eight switchable radiation patterns with 360 degree covering the azimuth plane. The operating frequency of this antenna is 2.96GHz. This will reduce the transmission power and extend the lifetime of the mote.

3 A Design of Switched Beam Antenna For Wireless Sensor Networks 3 Antenna Design To obtain the characteristics of the radiating structure of the designed switched beam antenna, the geometry of the two L shaped quarter wavelength slot antenna elements are firstly designed. The geometry of the proposed antenna elements array is given in Fig.1 The proposed antenna array has two L shaped quarter wavelength slot antenna elements. They are separated at a distance of quarter wavelength at reference frequency and they are perpendicular to each other. The L shaped slot antennas are separated at a distance of quarter wavelength to increase the gain and directivity. To obtain the geometrical pattern and to reduce the HPBW and to increase the gain the ground plane is designed with a trapezoidal shape. The shape and direction of the radiation pattern depends on the parameters t1 and t2. The gain in the main lobe of the direction pattern is 5.09dbi and in the azimuth plane the radiation pattern rotates about 45 degree from x axis. The dipole antenna produces high gain so as to reduce the power and will increase the lifetime of the mote. Figure 1: Structure of The Proposed Switched Beam Antenna Table 1: Parameters of Designed Antenna Parameters Value unit εr 4.7 h 0.8 mm e 1.5 mm l 18 mm ls 4.3 mm g 17.8 mm g s 6.1 mm t1 48 mm t2 11 mm t3 25 mm t4 20 mm k 4 mm

4 4 M.Sujatha, R.S. Bhuvaneswaran and D.kaviyarasan Antenna Structure The antenna has four arrays of radiating structure each with two L shaped quarter wavelength slot antenna elements in symmetrical planar structure. Each array rotates by 90 degree along the axis perpendicular to the xy axis. It is fed by a 50 ohm SMA connector at the center of the antenna and will provide geometrical symmetry of the L shaped antenna and this will maintain the feeding point away from the radiating elements. The efficiency is reduced by the proximity due to connectors, switches and the radiating elements. The feeding to the antenna elements is controlled by the RF switches, which interrupt the eight micro strip transmission lines. The digital circuit controls the RF switches by the signal cnt and it is powered through the lines Vdd and Gnd. The RF2 output is connected to the feeding line and it is connected to the RFC input when the cnt is set to 3V and the related antenna radiates. When the antenna is not radiating, the RFC input is connected to the open line RF1 by setting the cnt to 0V. The proposed switched beam antenna can switch among eight different directional radiation patterns spaced 45 degree by carefully setting the cnt value. Figure 2: RF Switch Result The electromagnetic properties of the proposed antenna are accurately measured by designing a cost effective prototype of the switched beam antenna. The size of the antenna is 10*10 cm and it is fabricated in a FR4 substrate with thickness M=0.8mm and dielectric constant εr = 4.7. The design parameters of the proposed switched beam antenna are given in table 1. The switching IC used is the Peregrine PE4283 RF Ultra CMOS switches with single pin CMOS logic. It has a ESD tolerance of 1.5kV, a low insertion loss of 0.5 db at reference frequency, a 33.5dB isolation between the output ports, a +3 V supply input with an operating band of 4GHz and a very low power supply current of 8µA. STM32W-EXT WSN boards with a 32 bit ARM microprocessor and an IEEE transceiver is used to study the radiation patterns.

5 A Design of Switched Beam Antenna For Wireless Sensor Networks 5 Figure 3: Design of Proposed Switched Beam Antenna 0 S11 m1 freq= 2.964GHz db(pavi2_mom_a..s(1,1))= M ag. [db] m Frequency Figure 4: Return Loss Graph of Proposed Antenna The return loss of the proposed switched beam antenna is -34.4dB at frequency 2.96GHz as shown in Fig 4. Since the return loss of the antenna is very low, the antenna is very efficient.

6 6 M.Sujatha, R.S. Bhuvaneswaran and D.kaviyarasan Figure 5: Radiation Pattern of Antenna 1 and 2 Figure 6: Radiation Pattern of Antenna 3 and 4 Figure 7: Radiation Pattern of Antenna 5 And 6

7 A Design of Switched Beam Antenna For Wireless Sensor Networks 7 Figure 8: Radiation Pattern of Antenna 7 and 8 Conclusion A switched beam antenna with four arrays of two L shaped quarter wavelength slot antenna elements arranged in symmetrical plane are presented in this paper for WSN applications. Eight digital control lines are used to select the appropriate radiation pattern depending on the WSN needs. The proposed switched beam antenna is compact and cost effective and it is very power efficient compared to the traditional slot antennas. References [1] 1.Anchora, L., Capone, A., Mighali, V., Patrono, L., Simone, F., A novel MAC scheduler to minimize the energy consumption in a Wireless Sensor Network, Ad Hoc Networks, vol. 16, pp , May [2] 2.Catarinucci, L., Colella, R., Del Fiore, G., Mainetti, L., Mighali, V., Patrono, L., Stefanizzi, M.L., A cross-layer approach to minimize the energy consumption in wireless sensor networks, International Journal of Distributed Sensor Networks, vol. 2014, [3] 3.S. Zhang, G. H. Huff, and J. T. Bernhard, A pattern reconfigurable microstrip parasitic array, IEEE Trans. Antennas Propag., vol. 52, no. 10, pp , Oct [4] 4.L. Catarinucci, S. Guglielmi, L. Mainetti, V. Mighali, L. Patrono, M. L. Stefanizzi, L. Tarricone, An Energy-Efficient MAC Scheduler based on a Switched-Beam Antenna for Wireless Sensor Networks, Journal of Communications Software & Systems, vol. 4, Jun [5] 5.L. Catarinucci, S. Guglielmi, L. Patrono, and L. Tarricone, Switchedbeam antenna for wireless sensor network nodes, Progress in Electromagnetics Research C, vol. 39, pp , [6] 6.L. Ming-Iu, W. Tzung-Yu, H. Jung-Chin, W. Chun-Hsiung, J. Shyh- Kang, Compact Switched-Beam Antenna Employing a Four-Element Slot

8 8 M.Sujatha, R.S. Bhuvaneswaran and D.kaviyarasan Antenna Array for Digital Home Applications, IEEE Trans. Antennas Propag., vol. 56, no.9, pp , Sept [7] 7.S. K. Sharma, L. Shafai, and N. Jacob, Investigate of wide-band microstrip slot antenna, IEEE Trans. Antennas Propag., vol. 52, no. 3, pp , Mar