Reconfigurable Four-Parasitic-Elements Patch Antenna ... - IEEE Xplore

IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 13, 2014

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Reconfigurable Four-Parasitic-Elements Patch Antenna for High-Gain Beam Switching Application Muzammil Jusoh, Student Member, IEEE, Thennarasan Sabapathy, Student Member, IEEE, Mohd Faizal Jamlos, Senior Member, IEEE, and Muhammad Ramlee Kamarudin, Senior Member, IEEE

Abstract—A reconfigurable beamforming of a four-parasitic-elements patch antenna (FPPA) for WiMAX application is presented. The proposed FPPA is successfully capable to steer the radiation pattern in azimuth planes (0 , 45 , 135 , 225 , and 315 angles) and in elevation plane (0 , 13 , 15 , 10 , and 12 ). This is realized in the unique form of four parasitic elements encircling the center main radiator. The activation of the parasitic required a shorting pin to the ground that indicates ON state condition, and vice versa. It is discovered in CST simulation software that the specified location of the pins are really significant to ensure the parasitic performs either as a reflector or director. Moreover, each of the shorting pins is linked to the RF p-i-n diode BAR5002v switch. Also, the FPPA is fabricated on a 130-mm square Taconic substrate. The proposed antenna design has a maximum gain of 8.2 dBi at all desired angles with a half-power beamwidth of 58 . Index Terms—High-gain antenna, p-i-n diode switches, reconfigurable parasitic antenna.

I. INTRODUCTION

T

HE HIGH-DATA-RATE communication, minimum bit error rate (BER), and robust to interference in wireless services are the main concerns over the past several years [1]. Therefore, an adaptive array or switched beam antenna is potential for the current necessity. Such an antenna is capable to direct the main beam toward the desired signal and suppress the antenna beam in the unwanted signal direction. Microstrip antenna with beam-switching capability has drawn a lot of attention due to the low cost, ease of fabrication, and easy integration with microwave devices [2]. However, the main challenge is to achieve beam-switching coverage angle of 0 –360 at the compact dimension of mm [3], [4]. Besides, the beam-steering antenna has a drawback to achieving a high-gain antenna at all desired directions [5], [6]. Moreover, Manuscript received October 08, 2013; revised October 31, 2013; November 12, 2013; and November 28, 2013; accepted December 16, 2013. Date of publication January 02, 2014; date of current version January 24, 2014. This work was supported by the Universiti Malaysia Perlis and ScienceFund GUP 900500085. M. Jusoh and T. Sabapathy are with the School of Computer and Communication Engineering (SCCE), Universiti Malaysia Perlis (UniMAP), Campus Pauh Putra, 02600 Arau, Malaysia (e-mail: [email protected]; [email protected]). M. F. Jamlos is with the Advanced Communication Engineering Centre (ACE), School of Computer and Communication Engineering (SCCE), Universiti Malaysia Perlis (UniMAP), Campus Pauh Putra, 02600 Arau, Malaysia (e-mail: [email protected]). M. R. Kamarudin is with the Wireless Communication Centre (WCC), Faculty of Electrical Engineering, Universiti Teknologi Malaysia (UTM), 81310 UTM Skudai, Malaysia (e-mail: [email protected]). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LAWP.2013.2296491

the literature shows that it is difficult to achieve a beam-steering antenna with the stability [7], [8]. For instance, the coarse-grained structure composed of two reflectors and a feeder is only capable to execute beam switching from to [9]. In other related work [7], the reconfigurable antenna is realized with a spiral antenna structure with four p-i-n (PIN) diode switches integration. Despite that, the antenna has a finite ground plane with dimension of 175 170 mm . At the azimuth plane, the beam steers 65 at -axis and 130 at -axis. At the elevation plane, the -axis. However, the beam steers 20 at -axis and 335 at antenna has unstable reflection coefficient. The measured is shifted to the right for 200 MHz. Therefore, the proposed four-parasitic-elements patch antenna (FPPA) design has to ensure that the is stable at all desired phi directions. Kamarudin et al. discovered in [10] that a disk-loaded monopole array antenna with coplanar waveguide feed is capable to achieve a switchable beam pattern. With the help of RF/microwave devices, such a beam can be steered to the elevation and azimuth planes. The switching capability can be realized using RF switches such as p-i-n diodes, varactor diodes, microelectromechanical systems (MEMs), and gallium arsenide field-effect transistors (GaAs FETs) [11], [12]. Such devices change the effective length of the proposed antenna radiator, thus providing reconfigurable beam ability. In this letter, a beam-switching antenna with high-gain performance is designed for WiMAX application (2.36–2.40 GHz). The antenna has successfully steered the beam to five directions; phi of 0 , 45 , 135 , 225 , and 315 with the respective theta of 0 , 13 , 15 , 10 , and 12 . To the best of the authors’ knowledge, none of the beam-switching antennas have achieved a high gain at all beam directions. The stack FPPA has successfully performed high gain of 9.0, 8.1, 8.2, 7.9, and 7.7 dBi, respectively. This can be achieved by implementing a single main radiator surrounded by four parasitic elements with a full ground plane at the back side of the substrate. To realize a reconfigurable beam antenna, all parasitic elements are connected to the p-i-n diode switches via shorting pin. Four p-i-n diode switches are integrated to the FPPA. The parasitic becomes a reflector when the diode is active and connected to the ground plane. In contrast, it acts as a director when not connected to the ground or the diode is in OFF state. The switching components are mounted on the different plane that is located 5 mm underneath the antenna to minimize the unwanted signal produced by the switching elements. The main radiator positioned in the middle of the structure is excited by the coaxial probe feed. Balanis said in [2] that the SMA port position is really crucial in order to get better impedance matching. The feed is therefore positioned in such

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Fig. 1. Simulation design of the stack FPPA. (a) Radiating element. (b) Ground plane. (c) Oblique view.

Fig. 2. Prototype of the FPPA. (a) Radiating element. (b) Ground plane. (c) Layout view. (d) p-i-n diode switches. (e) Side view.

a way to have good impedance matching for the antenna. Moreover, the proposed antenna has a physical substrate dimension of 130 mm square. The coaxial probe position, radiator radius, and aperture slot dimension have significant influence on the radiated circle surface current distribution and the impedance matching. II. ANTENNA DESIGN The proposed antenna has been designed on a 130-mm square Taconic substrate with a dielectric constant of 2.2, board thickness of mm, and tangent loss of 0.0009. Figs. 1 and 2 depict the simulation and prototype of the antenna. It has been designed in two layers: The upper layer is where the main antenna structures are located, while the bottom layer is mainly created for the p-i-n diode switches placement. Both layers are connected via shorting pins with a gap of 5 mm. The upper layer consists of a single main radiator on the center of the circular antenna and four parasitic elements denoted as parasitic A, B, C, and D. All parasitic elements are uniquely located around the radiator as depicted in Fig. 1(a). The FPPA implemented a full ground plane to achieve high-gain antenna by suppressing the unwanted back and side lobes. Moreover, the induce current is excited to the driven element via a coaxial probe. The feed is placed at - and -axes of 4 mm with an intersecting angle of 45 that gives an optimum impedance matching. The performances of such an antenna are significantly influenced by the dimension of the antenna ground plane, presence of slot, and radius of the radiator. Therefore, some optimizations on the antenna structures have been done. As a result, the optimum antenna dimension indicates that the driven element

Fig. 3. (a) Simulated and (b) measured reflection coefficient of the FPPA. Each p-i-n diode not mentioned is in ON state.

radius

mm and all parasitic elements have a radius of mm as depicted in Fig. 2(a). The optimization ensured that with these dimensions, the driven element and the parasitic help the overall antenna to be resonating from 2.36 to 2.4 GHz. All parasitic elements are positioned close to the driven element with a separation distance of 3 mm. In CST simulation, it has been identified that increasing the element spacing between the parasitic elements and the driven element has shifted the operating frequency to the higher resonant frequency. Meanwhile, the slot presence contributed to the better simulated efficiency of 96%. As illustrated in Fig. 1, all parasitic elements are positioned in the direction of 45 , 135 , 225 , and 315 to the main radiator. Such a parasitic arrangement contributed to the FPPA size compaction of 20% with equivalent performance as compared to the parasitic element arrangement of 0 , 90 , 180 , and 279 . The activation of the parasitic elements via a shorting pin to the ground indicates ON state, and the deactivation of parasitic requires an opening pin to the ground that leads to the OFF state. Parasitic element with the ON state performed as a reflector, while the parasitic with OFF state functioned as a director that will push and pull the radiation pattern, respectively. The concept of Yagi–Uda antenna has been applied in this research. The originality of this design is that the parasitic elements are connected to diodes by shorting pins to enable beam steering. The advantage of having a switching board underneath the radiating and parasitic elements is that this could reduce the effect

JUSOH et al.: RECONFIGURABLE FOUR-PARASITIC-ELEMENTS PATCH ANTENNA

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Fig. 4. Surface current distribution at 2.38 GHz. Each p-i-n diode that not mentioned is in ON state. (a) PIN A is OFF. (b) PIN B is OFF. (c) PIN C is OFF. (d) PIN D is OFF.

Fig. 6. Simulated and measured normalized beam pattern for cut. Each p-i-n diode that not mentioned is in ON state. (a) All switches are ON. (b) PIN A is OFF. (c) PIN B is OFF. (d) PIN C is OFF. (e) PIN D is OFF.

Fig. 5. Simulated 3-D beam-switching pattern. Each p-i-n diode that not mentioned is in ON state. (a) All switches are ON. (b) PIN A is OFF. (c) PIN B is OFF. (d) PIN C is OFF. (e) PIN D is OFF.

on the steering beam patterns. Each of the shorting pins is indicated as pin A, pin B, pin C, and pin D. These shorting pins are linked directly to the p-i-n diode switches as illustrated in Fig. 2(d). III. RESULTS AND DISCUSSION The simulated and measured of the FPPA is illustrated in Fig. 3(a) and (b), respectively. It can be observed that the proposed antenna has a similar simulated resonant frequency regardless of the p-i-n diode configurations. However, the measured depicts that there is a slight shift in the resonant fre-

quency and lower impedance matching compared to the sim. This is maybe due to the signal deterioration by ulated the switching components (diodes, inductors, and capacitors). However, the relatively small shift in the resonant frequency is acceptable for WiMAX application. Both simulated and measured antennas produced a bandwidth from 2.36 to 2.40 GHz under tolerable reflection coefficient of 10 dB. Since a driven element deals with four parasitic elements, a mutual coupling phenomenon is the significant factor that needs to be considered. The mutual coupling effect exists due to the electromagnetic interaction between the reflector and the director elements. It can be minimized with a sufficient interelement spacing (IES) and using an isolator. Therefore, each of the parasitic elements is separated to the other parasitic element with an IES of in order to achieve better antenna efficiency of 85%. This high element isolation can be observed through the H-field of surface current distribution. Fig. 4 shows the surface current distribution at 2.38 GHz of four p-i-n diode configurations. As PIN A is OFF in Fig. 4(a), more current has excited to the parasitic A, while other parasitics

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TABLE I CONFIGURATIONS OF P-I-N DIODE SWITCHES

gives significant contribution in terms of beam-switching angle. Details of the beam direction and switching sequence are tabulated in Table I. In practical, such an antenna is suitable for an application that requires a directional beam in one particular angle to have a more reliable connection with small losses in overall performance. IV. CONCLUSION

(B, C, and D) almost have null interaction. It can be observed in Fig. 4(b) that the surface current only exists at parasitic B with PIN B OFF. Fig. 4(c) and (d) depicts the surface current at parasitic C and D with PIN C and D OFF, respectively. At each specific PIN “OFF” state, all other unmentioned PINs are in the “ON” state. It is discovered that more current has distributed at the particular activation parasitic element according to the p-i-n diode configurations due to the least mutual coupling effect. Moreover, all the parasitic configurations have a circular current distribution that leads to an almost circular polarization. It is discovered that the changes of the p-i-n configurations do not influence the operating frequency, but lead to the changes of the beam pattern. The 3-D simulated radiated pattern is shown in Fig. 5. When all PINs are active, the stack FPPA achieved a maximum gain of 9.0 dBi. This can be considered as the default state where the beam pattern is at the broadside angle. On the other hand, for the situation when only one PIN is OFF and the remaining PINS are ON, the antenna produces a gain of 8.1 dBi (when PIN A is OFF), 8.2 dBi (when PIN B is OFF), 9.0 dBi (when PIN C is OFF), and 7.7 dBi (when PIN D is OFF) as shown in Fig. 5(b)–(e). The variance in gain may be due to the asymmetry of the p-i-n diode arrangement and the difference of shorting pin position for all parasitic elements. Apart from that, the dc lines and the biasing circuit at the bottom substrate also influence the measured gain. A change in the main-beam radiation angle is achievable by certain p-i-n diode configuration as shown in Fig. 6. It shows the polar graphs of beam-pattern measurements that are normalized to their peak values. It is realized that the E-field pattern is radiated on the -axis with the theta angle of 0 –360 . Fig. 6(a) shows the beam steer at 0 when all switches are ON. In Fig. 6(b), the proposed antenna has a radiation pattern with maximum gain at 13 with beamwidth of 55 , when p-i-n diode A is turned OFF. By turning OFF the p-i-n diode B, the main beam would be steered to 15 and would have a beamwidth of 56 as denoted by Fig. 6(c). Fig. 6(d) demonstrates a switching angle of 10 with beamwidth of 58 achievable by turning OFF the p-i-n diode C. In Fig. 6(e), the main beam is steered to 12 with beamwidth of 55 when the p-i-n diode D is OFF. It is worth noting that the beam switching is effectively achieved by the good coupling effect between the driven and the parasitic elements. Moreover, the optimum shorting pin position

A novel reconfigurable beam-switching microstrip antenna using parasitic element is successfully developed in this letter. It is discovered that the mutual coupling effect and parasitic element implementation contribute to the achievement of the beam-switching antenna at desired of 0 , 45 , 135 , 225 , and 315 . The FPPA is designed with a single main radiator, four parasitic elements, and a full ground plane. It is discovered in CST simulation software that the specified location of the pins has ensured the parasitic to perform either as a reflector or a director. It is shown through the measurements that the radiation patterns can be well steered at five different directions with the optimized dimension and position of the parasitic elements. The reconfigurable beam-switching ability is developed using p-i-n diode switches. These four p-i-n diodes are placed on the different Taconic substrates in order to avoid signal deterioration. The compact FPPA of 130 130 mm has a minimum gain capability of 8 dBi at the steered angle phi of 0 , 45 , 135 , 225 , and 315 with the respective theta of 0 , 13 , 15 , 10 , and 12 . Moreover, each steered angle has wider beamwidth of 58 . The compact FPPA structure could be a great candidate for point-to-point wireless applications in perturbed environments. REFERENCES [1] T. S. Rappaport, Wireless Communications Principles and Practice. Upper Saddle River, NJ, USA: Prentice-Hall, 2002. [2] A. B. Constantine, Antenna Theory Analysis and Design. New York, NY, USA: Wiley, 2002. [3] H. Liu, S. Gao, and T. H. Loh, “Compact dual-band antenna with electronic beam-steering and beamforming capability,” IEEE Antennas Wireless Propag. Lett., vol. 10, pp. 1349–1352, 2011. [4] H. M. Lee, “Pattern reconfigurable micro-strip patch array antenna using switchable feed-network,” in Proc. Asia-Pacific Microw. Conf., 2010, pp. 2017–2020. [5] M. T. Ali, M. N. Tan, T. A. Rahman, M. R. Kamarudin, M. F. Jamlos, and R. Sauleau, “A novel of reconfigurable planar antenna array (RPAA) with beam steering control,” Prog. Electromagn. Res. B, vol. 20, pp. 125–146, 2010. [6] T. Sabapathy, M. F. Jamlos, R. B. Ahmad, M. Jusoh, M. I. Jais, and M. R. Kamarudin, “Electronically reconfigurable beam steering antenna using embedded RF PIN based parasitic arrays (ERPPA),” Prog. Electromagn. Res., vol. 140, pp. 241–267, 2013. [7] S. V. Shynu Nair and M. J. Ammann, “Reconfigurable antenna with elevation and azimuth beam switching,” IEEE Antennas Wireless Propag. Lett., vol. 9, pp. 367–370, 2010. [8] Z. Li, H. Mopidevi, O. Kaynar, and B. A. Cetiner, “Beam-steering antenna based on parasitic layer,” Electron. Lett., vol. 48, no. 2, pp. 59–60, 2012. [9] Y.-B. Jung, A. V. Shishlov, and S.-O. Park, “Cassegrain antenna with hybrid beam steering scheme for mobile satellite communications,” IEEE Trans. Antennas Propag., vol. 57, no. 5, pp. 1367–1372, May 2009. [10] M. R. Kamarudin, P. S. Hall, F. Colombel, and M. Himdi, “Electronically switched beam disk-loaded monopole array antenna,” Prog. Electromagn. Res., vol. PIER 101, pp. 339–347, 2010. [11] M. F. Ismail, M. K. A. Rahim, and H. A. Majid, “Wideband frequency reconfiguration using PIN diode,” Microw. Opt. Technol. Lett., vol. 54, no. 6, pp. 1407–1412, Jun. 2012. [12] H. A. Majid, M. K. A. Rahim, M. R. Hamid, N. AsnizaMurad, and M. F. Ismail, “Frequency reconfigurable microstrip patch-slot antenna,” IEEE Antennas Wireless Propag. Lett., vol. 12, pp. 218–220, 2013. [13] H. W. Ott, Electromagnetic Compatibility Engineering. Hoboken, NJ, USA: Wiley, 2009.