Volume 114 No. 10 2017, 301-308 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu ijpam.eu Design and Simulation Of Circular Patch Log Periodic Microstrip Antenna Array With Frequency Reconfigurability Using IE3D Software Rajanarendra Sai 1, K.Sudha 2 & H.DPraveena 3 1 Sree Vidyanikethan Engineering College,Tirupati, India.. sai.rajanarendra@gmail.com 2 Sree Vidyanikethan Engineering College, Tirupati, India sudhak.ece@gmail.com 3 Sree Vidyanikethan Engineering College, Tirupati, India hdpraveena@gmail.com Abstract In this paper the design, simulation and analysis of a circular microstrip patch antenna with frequency reconfigurability using the log periodic technique has been described. Inset feeding Technique with a single transmission line has been used for feeding the three elements of circular shaped microstrip patches. The Log periodic Circular Microstrip array operates over 2.90 GHz to 3.4GHz. Three Diodes are placed at the transmission line and they can be reconfigured to operate the designed antenna over two sub-bands based on their switching conditions. Simulation results for parameters like return loss and gain for every sub bands were presented and discussed. Key words: log-periodic antenna array, reconfigurability, wideband, microstrip, PIN diodes. 1 Introduction Conventional antennas don t have the ability to provide diverse functions like changes in the operation frequency, polarization, and radiation pattern, where as the reconfigurable antennas have such ability and they have received more attention, especially with the proliferation of wireless Communication technologies. The ability of reconfiguration can be embedded in to antennas by many techniques, which causes the redistribution of antenna currents leading to alteration of electromagnetic fields across the antennas effective aperture. Importantly, Reconfigurable antennas can adapt to the changes in system requirements or environmental changes like change in operating frequency, radiation pattern, polarization or enhanced bandwidth. The concept of reconfigurability has become required feature of modern RF systems for wireless communications. Reconfigurable antennas find their potential applications in near future wireless systems like cognitive radio [1], and multi frequency communication. Electrical Reconfigurability can be incorporated by using MEMS devices [2], Varactor diodes or PIN diodes [3]. The features of PIN diodes like ease of use, cost effectiveness, efficiency and reliability in dynamic bandwidth allocation has made them default choices in incorporating electronic tuning within the antenna structures. The advantage of frequency reconfigurable antennas has the ability to change dynamically the frequency of operation and can be reconfigured into any frequency band in wideband range, thereby enabling the ability for using multiple antennas. transmission or reception over a single antenna instead of 301
Patch antennas are widely used structures for different types of wireless applications, like Mobile Internet devices and smart mobile phones. Patch antennas offers uniform radiation pattern over broadside. So, a lot of effort has been put into extending their operation frequency from a single frequency to cover multiple bands of frequency by reconfiguration. In [3], Yang and Rahmat Sami presented a way to construct a patch antenna with reconfiguration of frequency by using a switchable slot in to antenna structure. Across the vertical slot, diode switch is placed with a cut in the centre of the patch. When the switch is ON, the resonance of the first patch for the horizontal main current is slightly altered compared the switch when it is turned OFF; the current is forced to move around the slot and travels a longer path which results in decrease of patch antenna resonant frequency. Recently, switchable slots have been proposed on the ground plane for enabling frequency reconfiguration of the patch antenna design [4]. In this paper, a circular patch log-periodic reconfigurable antenna array with the scaling factor of 1.05 has been designed and simulated to meet the antenna parameters like gain, radiation pattern, and return loss. The proposed antenna has been designed from the combination of three circular patches to form an antenna array by using the log periodic technique. The log periodic antennas can select required band of operation from wideband than other wide band antennas with ease, as each of the element radiating at different frequencies. The performance of antenna has been estimated on several parameters like radiation pattern, return loss, gain, directivity and bandwidth by performing simulation of the designed antenna structure using IE3D software. 2 Antenna Design The top view of the proposed Circular patch log periodic antenna array with reconfigurability is as shown in figure 1. The feature of frequency reconfigurability is verified by configuring the state of PIN diodes to ON or OFF. This designed antenna operates over the frequency band from 2.92 GHz to 3.40 GHz with two different sub bands of operation. Three circular patches with a log-periodic array formation with inset feeding are connected on the top of the substrate to a 50 Ω micro strip transmission line. For, the antenna structure, a FR4 epoxy substrate with dielectric constant of 4.5, with 1.6 mm thickness and loss tangent of 0.019 has been considered. Microstrip antennas have very narrow bandwidth. Broadband Microstrip antennas can be implemented using log periodic technique. The design principle for wideband microstrip antenna with log periodicity requires an array of patch antennas with the dimensions and also the spacing of the patches are increased in a log periodic manner, so it results in the performance in periodic with the logarithm of frequency. The diameter (d) of the circular patch and the distance from inset feed line are related to the scaling factor (τ) by equation as shown below. d d I I m 1 m 1 (1) Initially a circular patch has been designed to have resonant frequency of 3 GHz and it has the diameter of 13.81 mm and it has been scaled to a factor of 1.05 to get the second circular m m 302
patch to operate at resonant frequency at 3.15 GHz with the diameter of 13.15 mm. The second circular patch diameter by same scaling factor to obtain the third patch diameter of 12.52 mm with a resonant frequency at 3.30 GHz. The circular patch is placed apart by half of wavelength, thus resulting in a forward radiation pattern and reducing the effect of mutual coupling. Reconfiguration can be achieved by the RF PIN diodes by integrating them with Centre feed transmission line as shown in fig.1 to act as switches and can be controlled to have ON/OFF mode. For the simulation purpose, the switching action of PIN diodes is modelled by an opening and shorting with the transmission line. So, metal stripes 3.2mm x 1.5 mm have been replaced for PIN diode to represent the ON state of the switch at the transmission line. Similarly an slot of dimension 3mm x 1mm have been replaced for PIN diode to represent the OFF state of the switch. When all switches are in ON state wideband operation can be achieved. By changing the state of the switches, the required band of operation can be selected. Here, two sub-bands have been achieved by altering the states of switches as tabulated in Table 1. The first band operation has been achieved by switching the first two PIN diodes switches ON while the PIN diode at position three is switched OFF. While band two operation has been achieved when first PIN diode is switched OFF while the other two PIN diodes are in switched ON. The sub bands operation is shown in Table 1. Fig. 1. Proposed Three Element Circular Logperiodic Antenna Array(Top View) 303
Fig. 2. PIN diode Switch Modelling in simulation Table 1. Switching Conditions No. of the PIN diode WIDE BAND SUB BAND 1 SUB BAND 2 1 ON ON OFF 2 ON ON ON 3 ON OFF ON 3 Simulation Results The proposed log-periodic circular microstrip patch antenna array is simulated on IE3D software platform to evaluate the performance of the designed antenna. The return loss characteristics of the wideband operation are as shown in fig.3 where all the pin diodes are in ON state. Fig. 4 shows the return loss characteristics for two different sub different bands are for different switching condition of PIN diodes. The log-periodic micro strip antenna operates from 2.9 GHz until 3.4 GHz or over 15.31 % bandwidth. The different sub bands bandwidth for each band is as shown in Table II. The Simulated Antenna array gain for wideband operation is as shown in fig.5 where all the pin diodes are in ON state. While the gain after simulation for sub bands are as shown in fig. 6. The gain and directivity characteristics for each of the band are given by Table 3. 304
Fig. 3. Return Loss characteristics for wideband of operation. Fig. 4. Return Loss characteristics for the two sub-bands 305
Fig. 5. Simulated Gain Response for Wide band of operation Fig. 6. Simulated Gain vs Frequency response for two sub-band operation. Table II. Comparison of Return loss Characteristics BAND F L GHz F C GHz F H GHz B.W (%) B.W (MHz) WIDE 2.92 3.16 3.40 15.31 484 BAND1 2.95 3.08 3.21 8.63 266 BAND2 3.09 3.23 3.38 9.04 292 Table III. Comparison of gain and directivity BAND FREQUENCY FC GHz Max. Gain (dbi) Max. Directivity (dbi) 306
WIDE 3.16 3.69 8.69 BAND 1 3.08 3.20 8.31 BAND 2 3.23 4.53 9.37 The realized gain at all frequency bands is about 3.2 db to 5 db and the directivity of the antenna is about 8 db for various sub bands as tabulated above. 4 Conclusion The proposed Log-periodic Circular Microstrip Antenna with frequency reconfigurability has been design and simulated. It operates from 2.9 GHz to 3.4 GHz with realised gain of 3 dbi to 6 dbi for directivity of 8 dbi to 10.5dBi. It has been shown that the required band of operation can be achieved by choosing different switching combinations. The designed antenna operates over two sub-bands over Wide band of operation by switching ON two groups of patches. For each of the frequency of operation band, a return loss, gain and radiation pattern have been obtained are in acceptable range. Hence, the proposed antenna structure with more elements with further wide bandwidth could be used for cognitive radio, which requires sensing over a wideband of frequency and dynamically switching over the band that is being sensed. References 1. B. Z. Wang, S. Xiao and J. Wang, Reconfigurable patch-antenna design for wideband wireless communication system, IET Microwave Antennas Propagation, vol.1,issue 2, pp. 414-419, 2007. 2. A.H.Ramadan, K.Y.Kabalan, A.El-Hajj, S.Khoury and M.Al-Husseini, A Reconfigurable U-Koch Microstrip Antenna for Wireless Application, Progress In Electromagnetics Research, PIER 93, pp.355-367,2009. 3. F. Yang and Y. Rahmat-Samii, Patch antennas with switchable slots (PASS) in wireless communications: Concepts, designs, and applications, IEEE Antennas Propagation Magazine., vol. 47, pp. 13 29, Feb. 2005. 4. E. Erd il, K. Topalli, M.Unlu, O. A. C ivi, and T. Akin,Frequency tunable patch antenna using RF MEM S technology, IEE E Trans. Antennas Propag., vol.55, no.4, pp.1193 1196, Apr 200 5. S. Shelley, J.Costantine, C.G.Christodoulou, D.E.Anagnostou, and J.C.Lyke, FPGA controlled switch reconfigured antenna, IEEE Antennas Wireless Propag.Lett, vol.9, pp. 355 358, 2010. 6. D. Peroulis, K.Sarabandi, and L.P.B.Katehi, Design of reconfigurable slot antennas, IEEE Trans Antennas Propag., vol.53, no.2, pp.645 654, Feb. 2005. 7. A Grau, J.Romeu, M.Lee, S.Blanch, L.Jofre and F.DeFlaviis, A dual linearly polarized MEMS reconfigurable antenna for narrowband MIMO communication systems, IEEE Trans. Antennas Propag., vol.58, no.1, pp.4 16,Jan2010. 8. J. T. Bernhard, Reconfigurable Antennas, Rafael, CA, USA: Morgan and Claypool. 307
308