INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN ISSN 0976 6464(Print) ISSN 0976 6472(Online) Volume 4, Issue 4, July-August, 2013, pp. 226-231 IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2013): 5.8896 (Calculated by GISI) www.jifactor.com IJECET I A E M E VARACTOR DIODE LOADED DOUBLE SQUARE RECONFIGURABLE MICROSTRIP PATCH ANTENNA FOR WIRELESS APPLICATIONS 1 Chandrappa D.N., 2 P.A.Ambresh, 3 P.V.Hunagund 1, 3 Microwave Research Laboratory, Department of PG Studies and Research in Applied Electronics, Gulbarga University, Gulbarga (Karnataka) 585 106, India. 2 Central University of Karnataka, Gulbarga Gulbarga University Campus, Gulbarga (Karnataka) 585 106, India ABSTRACT In this paper, a frequency reconfigurable double square microstrip patch antenna is discussed and presented. By incorporating four bridges in between the two square patches, a characteristics of flat input resistance and a linear input reactance across a bridge with multiple bands are obtained in comparison with conventional patch antenna. The designed antenna also achieves a tunable frequency range from 1.11 GHz to 3 GHz, with a size reduction of 90 % at resonant frequency. Designed antenna finds application in dual-mode multiband WLAN transceivers which operate over a wide range of frequency as designated by TRAI for wireless communication. Measured and simulated data of return loss (RL) and radiation patterns are also presented. Keywords: Frequency reconfigurable antenna, square patch, multiple bands, WLAN, bandwidth. I. INTRODUCTION Reconfigurable antennas have recently received significant attention for their applications in communications, electronic surveillance and counter measures by adapting their properties to achieve selectivity in frequency, bandwidth, polarization and gain. Compared to broadband antennas, reconfigurable antennas offer the advantages of compact size, similar radiation pattern for all designed frequency bands, efficient use of electromagnetic spectrum and frequency selectivity useful for reducing the adverse effects of co-site interference and jamming. Multi-frequency reconfigurable microstrip antennas can offer additional advantages of frequency reuse for doubling the system capability and polarization diversity for good performance of reception and transmission or to integrate the receiving and transmitting functions into one antenna for reducing the antenna size [1]. Reconfigurable antennas are useful for wireless applications, which require an efficient use of the 226
electromagnetic spectrum and low interference between adjacent channels. This type of antenna provides wideband tuning range achievable without deteriorating the radiation pattern. Electromechanical or electrical switches such as RF MEMS, p-i-n diodes and varactors have been used for reconfigurable antennas design. Although RF MEMS for specific antenna designs can be used without bias lines and even though they exhibit high Q and low loss, they require expensive equipment, more fabrication time and cost. In contrast, reconfigurable antennas with p-i-n diodes or varactors which are simpler to fabricate. Antennas, when loaded with active elements like varactor, the tuning linearity depends strongly on the varactor characteristics [2]. Reconfigurable square patch antenna has been investigated for multiple band operation in the wireless applications. Hence, microstrip antennas loaded with active devices are increasingly being used for many wireless applications because of its low profile and light weight advantages [3]. In this paper, a design of simple multiband double square patch antenna is presented. Two square patches, which configure for multiband frequency are obtained by connecting two square patches each other by 4-briges. The important role of bridge is to have connectivity of each square patch to operate antenna in multiple frequency bands. In addition, the varactor diodes are connected to bridges which have a role of tuning the frequency bands by changing bridge width (BW). By adopting this technique, shift in frequency band is achieved by changing the bridge widths (BW). Double square patch microstrip antenna is operated at 1.1 GHz, 1.4 GHz, 1.7 GHz, 2.1 GHz, 2.7 GHz frequencies for the solution of Global positioning system (GPS), Digital communication system (DCS), satellite DMB, WiMax frequency bands respectively. II. ANTENNA CONFIGURATION Fig. 1(a) shows the fabricated geometry of conventional square patch antenna. The square patch is printed on the dielectric substrate fed by microstrip feedline. The dielectric substrate has permittivity ε r = 4.4 and thickness h = 1.6 mm. The size of rectangular substrate length L = 107 mm and width W = 67.6 mm. Fig. 1(b) shows simulated results of return loss (RL) versus frequency characteristics and Fig. 1(c) shows measured results of return loss (RL) versus frequency characteristics for the proposed conventional antenna. Fig:1 (a) Conventional antenna (b) Simulated Return loss for conventional Antenna 227
(c) Measured Return loss for conventional Antenna These simulated and measured results are in good agreement with each other. Fig. 2(b) shows the geometry of fabricated reconfigurable double square patch antenna. The inner square patch (P 1 ) in the center configures for lower frequencies and its square width is 13 mm. The outer square patches (P 2 ) configure for higher frequencies and its square width is 28 mm. Four-bridges make a connection between inner patch (P 1 ) and outer patch (P 2 ). Operating frequency of antenna is acheived by changing bridge width (BW) from 1 mm to 4 mm. Varactor diode is integrated with the bridge slot, and is used to tune the operating frequencies without affecting the radiation characteristics. Desired operating frequency values can be obtained by incorporate the active devices, i. e, varactor diode, which will take some amount of power from the source (Network analyzer) through SMA connector. This active device will energize itself and provides a long path for current to flow in the radiating patch. This result in shifting of frequency hence reduction in antenna size is observed. Transmission lines are avoided in between the non-linear components and the radiating patch, so that, added noise and ohmic losses are suppressed and the resulting structure is more compact [4-5]. III. RESULTS AND DISCUSSION Reconfigurable double square patch antenna is analyzed using Zeland IE3D-full wave simulator and also practically tested on Vector Network Analyzer (VNA). Return loss (RL) and radiation pattern for linear polarization are simulated and measured. Fig. 2(c) shows comparison between simulated and measured return loss at bridge width (BW) = 2 mm with one diode. From the figure it is clear that antenna is operating at multi frequencies 1.1 GHz, 1.4 GHz, 1.7 GHz, 2.1 GHz and 2.7 GHz respectively. 228
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 6464(Print), ISSN 0976 6472(Online) Volume 4, Issue 4, July-August August (2013), IAEME Fig.2 (a) Reconfigurable antenna with BW = 2mm with one diode (b) Photograph of the fabricated antenna (c) Simulated and measured return loss for proposed reconfigurable econfigurable antenna Comparison of return loss (RL) for the three different bridge widths, BW = 1 mm, BW = 2 mm, BW = 2 mm with two diodes are shown in Fig. 3 (a), 3 (b) and 3 (c) respectively respectively. Fig: 3(a) (a) Return loss for BW=1mm without diode 229 (b) Return loss for BW=2mm without diode
(c) Measured Return loss for BW=2mm with two diodes Fig: 4. Radiation pattern for proposed reconfigurable antenna For bridge width BW=1, the operating frequencies are 1.1 GHz, 1.7 GHz and 2.0 GHz are obtained. For bridge width BW=2, the operating frequencies are 1.1 GHz, 1.9 GHz and 2.1 GHz are obtained. For bridge width BW=2 mm with two diodes, the operating frequencies are 1.12 GHz, 1.18 GHz, 1.6 GHz, 1.7 GHz, 2.1 GHz, 2.7 GHz, 834 MHz and 1.7 GHz are obtained. The wide bridge width makes strong connection between outer patch (P 2 ), which is operated at higher frequency. In addition, operating frequency moves to the highend frequency by increasing bridge width as shown in Fig. 3(c). Also, it is seen that, the operating frequency moves to the low frequency band by decreasing bridge width (BW) as shown in Fig. 2(c). These simulated results are obtained using IE3D software. Measured normalized radiation pattern for 2.1 GHz at bridge width BW = 2 mm is shown in Fig.4. By inserting a varactor diode at second bridge slot will generate multi frequency bands useful for different applications. IV. CONCLUSION A multi band reconfigurable double square patch antenna is designed, simulated, fabricated and tested for various wireless applications, which operates for 1.1 GHz, 1.4 GHz, 1.7 GHz, 2.1 GHz, 2.7 GHz frequencies having wide multiband characteristics suiting for wireless applications. From the results it is also clear that, change in bridge width (BW) will affect multifrequency band. This concept can be simply adopted to design other antennas operating for different frequency band. 230
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