A Beam Switching Quasi-Yagi Dipole Antenna - IEEE Xplore

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 61, NO. 10, OCTOBER 2013

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A Beam Switching Quasi-Yagi Dipole Antenna Pei-Yuan Qin, Member, IEEE, Y. Jay Guo, Senior Member, IEEE, and Can Ding, Student Member, IEEE

Abstract—A high gain beam switching pattern reconfigurable quasi-Yagi dipole antenna is presented for wireless local area network (WLAN) systems at 5.2 GHz. The antenna consists of a microstrip-to-coplanar stripline (CPS) balun, the length of which can be controlled by using PIN diodes. The change of the length of the balun allows the currents on the two arms of the dipole to have different phase differences, thereby making the antenna operate at three states with the E-plane maximum beam direction towards 20 , , and 0 , respectively. In order to validate the design method, a prototype of the proposed antenna with a practical biasing network was fabricated and measured. Measured results on the reflection coefficients, radiation patterns, and realized gains for three operating states are provided, which agree well with the numerical simulations. Index Terms—Beam switching, dipole antennas, microstrip antennas, pattern reconfigurable antennas, quasi-Yagi antennas.

I. INTRODUCTION

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ITH the rapid development of wireless communications technologies and the growing demand for high data rate and robust wireless communications networks, there has been a strong interest in reconfigurable antennas. Pattern reconfigurable antennas have gained substantial attention due to their abilities to manipulate the radiation characteristics. They have the potential to reduce the interference by altering the null positions, to save energy by directing the signal toward intended users, and to provide larger coverage by steering the main beam. In addition, the pattern diversity provided by pattern reconfigurable antennas can be exploited by the multiple-input-multiple-output (MIMO) systems to increase the system capacity and/or link quality [1]. In the last ten years, great efforts were devoted to the design of pattern reconfigurable antennas [2]–[18] based on microstrip patch antennas due to their advantages of low profile, low cost, and compactness. Basically, the work can be classified into three categories in terms of the radiation patterns the antenna provided. The first one focuses on the reconfiguration of the main beam shape, such as reconfiguring the radiation patterns between end-fire and boresight [2], switching between boresight and conical patterns [3], [4], and changing the radiation patterns between an almost omni-directional pattern and two end-fire Manuscript received February 06, 2013; revised May 02, 2013; accepted June 18, 2013. Date of publication July 24, 2013; date of current version October 02, 2013. P.-Y. Qin and Y. J. Guo are with CSIRO ICT Centre, Marsfield, NSW 2122, Australia (e-mail: [email protected]). C. Ding is with the CSIRO ICT Centre, Marsfield, NSW 2122, Australia and also with the Key Laboratory of Wide Band-Gap Semiconductor Materials and Devices of Ministry of Education, Xidian University, Xi’an, Shaanxi 710071, China. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2013.2274635

patterns whose main beams are directed to exactly opposite directions [5], [6]. The second one concentrates on changing the null positions either in a discrete way using PIN diodes [7] or a continuous way using varactor diodes [8]. The third one features the capability of steering the main beam direction [9]–[18]. Some antennas were proposed to steer the main beam to predefined directions by using electronic switches, such as PIN diodes, to activate one or several elements out of a few radiators. A four-element L-shaped antenna array was proposed that can achieve beam steering over 360 in the azimuth plane with a gain around 0.5–2.1 dBi [9]. Also, spiral structure was employed to change the main beam direction by altering the length of the spiral. In [10]–[12], rectangular single-arm spiral antennas were designed to change the main beam over five directions, three directions and four directions, respectively. The gains of the antennas in [10]–[12] are between 3–6 dBi, 4 dBi, and 1.1–4.6 dBi, respectively. In addition, work has gone into developing beam-steering antennas based on the Yagi-Uda type array [13]–[16]. Usually, such antennas have one driven element and several parasitic elements integrated with switches. By controlling the switches, the directive and reflective roles of the parasitic elements can be changed, thereby changing the main beam direction. The driven element can be either a microstrip dipole [13], a microstrip patch [14], [15], or a wire antenna [16]. Instead of incorporating electronic switches to the parasitic elements of the Yagi-Uda antenna array, movable liquid metal parasitics have also been used to change the physical positions of the director and reflector to accomplish beam steering [17]. Recently, a novel fixed-frequency electronically beam steerable leaky-wave antenna was introduced [18]. The antenna can provide beam scanning in an angular range from 9 to 30 with a gain higher than 11 dBi at 5.6 GHz. However, the bulky three-dimensional waveguide structure makes it hard to be integrated with mobile wireless devices. While there have been substantial advances in the design of pattern reconfigurable antennas, it is found that most of the reported microstrip beam-steering antennas suffer from the low realized gain, which may significantly limit their applications. In this paper, a high gain beam-switching pattern reconfigurable quasi-Yagi dipole antenna is proposed for the first time. It is capable of directing the E-plane main beam direction towards , or 0 with a realized gain between 7.5 dBi either 20 , to 10 dBi. Furthermore, in contrast to the reported pattern reconfigurable Yagi-Uda antenna arrays [13]–[17], a novel pattern reconfiguration mechanism, which is changing the length of the microstrip-to-coplanar stripline (CPS) balun, is adopted to achieve beam switching. Specifically, the length of the balun affects the phase difference of the currents on the two arms of the dipole. Different phase differences of the currents lead to different E-plane main beam directions. In this work, PIN diodes

0018-926X © 2013 IEEE

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are used to control the length of the balun, thereby enabling the proposed antenna to steer the beam electronically. The proposed antenna is intended for low-power devices, such as low-cost point-to-point backhauls employing WLAN nodes where beam steering is a desirable feature to mitigate the effect of antenna misalignment. In this paper, we extended the work reported in [19] significantly by giving an updated antenna reconfiguration mechanism and showing the antenna structure with an entire biasing network of the PIN diodes. In addition, the simulated and measured reflection coefficients of the proposed antenna are given. Furthermore, the measured radiation patterns and realized gains are described with a discussion on the effects of the PIN diodes on the antenna gain. The paper is organized as follows. In Section II, the operating principle, the antenna structure, and the biasing networks for the PIN diodes are described. Simulated and measured performance of the antenna is provided and compared in Section III. A discussion on the effects of the biasing network on the antenna radiation patterns is given in Section IV. The paper concludes in Section V with a summary and suggestions for further work.

Fig. 1. Currents on a half-wavelength dipole.

Fig. 2. E-plane maximum beam direction as a function of the phase difference of the currents on the two arms of the dipole.

II. PATTERN RECONFIGURABLE ANTENNA DESIGN A. Pattern Reconfiguration Mechanism The basic structure of the proposed pattern reconfigurable antenna is a planar quasi-Yagi dipole antenna [20] that consists of a truncated ground as the reflector, a dipole driver, and one or more directors. To help explain the operating mechanism of the antenna, we start with a single dipole antenna in the following. A very thin half-wavelength dipole oriented along the -axis is shown in Fig. 1. When the currents on the two arms of the dipole are of the same phase, the current distribution is given by , and where , is the propagation constant, and is equal to a quarter of wavelength. Then, the normalized electric-field pattern can be written as [21] (1) In this case, the maximum beam of the antenna in the E plane plane) is towards . If there is a phase difference ( between the currents on the two arms, (2) the normalized electric-field pattern is given by

(3) , (3) is identical to (1). Using (3), for each , the When value of corresponding to the maximum value of can be calculated, which is plotted in Fig. 2. From Fig. 2, it is seen that the maximum beam direction is almost a linear function

of the current phase difference . For , the maximum beam direction can be changed from to . With respect to , a beam-tilted range from to 43 is realized. For example, when , the maximum beam direction is not tilted, which is at . When is equal to 97 and , the maximum beam direction is tilted by 20 and , respectively. Therefore, if the phase of the currents on the dipole can be manipulated, the main beam of the antenna in the E plane can be steered, while the radiation pattern in the H plane ( plane, ) does not change with the phase variation. The above mechanism can be applied to quasi-Yagi dipole antennas to achieve beam steering. Compared to a dipole antenna, a quasi-Yagi dipole antenna has a reflector and one or several directors which can affect the beam steering range. However, as the dipole driver of the quasi-Yagi antenna has a dominant role in controlling the beam direction, the beam scanning can still be realized by changing the phase difference of the currents on the dipole. But, as shown in Section III, the actual beam-steering angle is limited by the sidelobe level that increases with the steering angle. In this work, in order to validate the reconfiguration mechanism, a beam steering range of to 20 is chosen. In addition, we aim to realize the beam steering in a discrete way by using PIN diodes, thus resulting in a switched beam pointing to three directions , 0 , and 20 . It should be noted that the beam can also be steered continuously by using varactor diodes, which is out of the scope of this paper. B. Antenna Structure The configuration of the proposed antenna is shown in Fig. 3. A 1.27-mm-thick Rogers 6010 substrate (dielectric constant 10.9) is used with metallization on both sides. As shown in Fig. 3(a), the top side of the substrate consists of a microstrip feed, an impedance transformer, a broad-band microstrip-to-

QIN et al.: A BEAM SWITCHING QUASI-YAGI DIPOLE ANTENNA

Fig. 3. Schematics of the proposed antenna: (a) whole structure; (b) balun of the antenna. TABLE I DIMENSIONS OF THE PROPOSED ANTENNA

CPS balun, a dipole driver fed by the CPS, and two tilted rows of directive strips. The bottom side is a truncated ground, serving as the reflector. The dimensions of the antenna are given in Table I. The initial values of these parameters are based on the analysis given in [20], and then a trial-and-error method is used to further optimize them according to the antenna performance. For parameters , their values will be studied in the last paragraph of this sub-section. The time domain solver

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of commercial full-wave simulation software CST Microwave Studio [22] was used to conduct the numerical analysis. Usually, a design for maximizing the gain of a Yagi-Uda antenna requires a non-uniform director length and spacing. In this work, the directive strips are of the same length and the spacing between two adjacent strips is identical in order to reduce the design complexity. It should be noted that the orientation of the rectangular coordinate used in Fig. 3 is different from that of Fig. 1 for the ease of showing the radiation patterns. The microstrip-to-CPS balun is used to introduce a phase difference for the currents on the two arms of the dipole. Details of the balun are shown in Fig. 3(b). It can be seen that the balun is a symmetrical structure with respect to the line . Therefore, we only describe the balun above the line . The right-hand part of the balun is split into three sections with lengths of , respectively, and the left-hand part is split into two sections with lengths of and , respectively. The gap between each section is connected by PIN diodes. The width of the gap for the PIN diodes is . In addition, the second section of the right-hand part of the balun with the length of is split into two smaller sections by a capacitor with a gap . This capacitor is used for biasing purpose which will be described in the next sub-section. Conventionally, the directors of a quasi-Yagi dipole antenna are placed horizontally (parallel to the dipole driver) to direct the maximum beam towards the end-fire direction . However, it is found that when the beam is steered away from the end-fire direction, the original horizontally located directors can reduce the beam scanning range and the antenna gain. This is because the directors are not parallel to the titled beam direction any more. In order to increase the beam steering range and maintain the antenna gain, two tilted rows of metal strips are placed in front of the dipole driver with 6 strips on each row, which is shown in Fig. 3(a). To a certain extent, the tilted angle of the directive strips determines the maximum steering range. In this work, it is made to be close to the desired antenna beam tilted angle. Furthermore, a small gap is etched on each strip to split it into two short parts with PIN diodes inserted into the gaps. When the PIN diodes are switched on, the two short strips are connected to perform as a director. When the PIN diodes are switched off, the two short strips are disconnected and they do not serve as directors, thereby having little effect on the far-field radiation pattern. In this way, the PIN diodes can be used to choose the proper directors for a certain main beam direction. To be specific, when the PIN diodes are switched on and the diodes are switched off, only the left-hand row of strips perform as directors and they facilitate the beam tilt towards the left-hand side with respect to the end-fire direction. Similarly, when the PIN diodes are switched on and diodes are switched off, the beam tilt towards the right-hand side is enhanced. When both sides of the diodes are switched on, two rows of directors maintain the beam towards the end-fire direction. By switching between the different states of the PIN diodes on the balun, the lengths of the current path on the right-hand and left-hand parts of the balun can be changed, thereby altering the phase difference of the currents on the dipole arms. According to the PIN diodes orientation shown in Fig. 3(b), the

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TABLE II DIFFERENT POLARIZATION STATES OF THE PROPOSED ANTENNA

antenna can operate in three states. For State I, diodes , , and the diodes on the two rows of directive strips (diodes and ) are switched on, and all the others are switched off. The phase difference of the currents on the left-hand and right-hand arms of the CPS is , where is the propagation constant in the substrate. According to (3), if there is no phase difference between the currents on the two arms of the dipole driver, the beam would not be tilted. In order to have a 0 phase difference of the currents on the dipole, the phase difference of the currents on the CPS should be 180 due to the differential input for the dipole. Therefore, should be designed to be ( is the guided wavelength). This way, the maximum beam directs at (end-fire direction) and an initial value of can be obtained. As the PIN diodes and capacitors inserted into the balun can also affect the phase difference, a trial-and-error method is employed to further optimize . For State II, diodes , , and the diode group are on, and all the others are off. In this case, the phase difference of the currents on the CPS is . According to (3), the phase difference of the currents on the dipole should be 97 in order to make the maximum beam in E plane ( plane) radiate towards direction. Similar to State I, (3) is used as a starting point to determine the value of , and then further optimization is carried on. For State III, diodes , , and diode group are on, and all the others are off. The phase difference of the currents on the CPS is . The maximum beam direction can be directed towards by optimizing . The possible operating states of the reconfigurable antenna and the corresponding diode states are summarized in Table II. C. DC Biasing Network In this paper, PIN diodes (MA4FCP300) [23] are used for the proposed antenna. According to the PIN diode datasheet, the diode is modeled as a 4 resistor for the ON state and a parallel circuit consisting of a capacitor of 0.04 pF and a resistor of about 20 for the OFF state in the simulation using CST Microwave Studio. The biasing networks for the PIN diodes on the balun and on the directive strips are shown in Fig. 3. As shown in Fig. 3(b), two dc biasing voltages are utilized to control the diodes on the balun. Voltage is applied to the diodes , , , and through the metallization of the microstrip line and the impedance transformer. This dc biasing voltage and the RF signal are simultaneously fed through the coaxial probe by using a bias tee. Two inductors (15 nH) are used to create a dc closed circuit for diodes while chocking the RF signal. Metallic and are the dc ground for diodes and

diodes , respectively. Inductors (15 nH) are placed between the balun and vias to chock the RF signal. According to the orientation of the PIN diodes, when voltage is negative, diodes and are switched on and diodes and are switched off, and vice versa. Voltage is applied to the diodes and . This biasing voltage is isolated from the RF signal by using a low-pass filter that is composed of a surface-mount inductor (15 nH), a capacitor (5.6 pF), and a metallic via. Metallic is the dc ground for diodes (d). When voltage is negative, diodes are switched on and diodes are switched off, and vice versa. Voltages and are isolated by capacitors (5.6 pF) mounted across the gaps of the second section (its length is ) of the right-hand side balun. For the diodes on the director, as shown in Fig. 3(a), two dc biasing voltages and are used for the diodes on the left-hand and right-hand rows of the directive strips, respectively. For the diodes on each side, very thin (0.15 mm width) metallic biasing strip lines are used together with a metallic via connected to the ground to form a dc closed circuit. In order to mitigate the effects of the biasing lines on the antenna performance, the strip lines are broken down into small sections and the gaps between the sections are bridged with inductors. For simplicity, we name such biasing strip line as inductive biasing line. It should be pointed out that in Fig. 3(a), the inductors between the gaps are not drawn for the sake of the clarity of the antenna structure. But the inductors are shown in a zoomed-in picture of a certain part of the inductive biasing line. It is found that the shorter the small sections, the less influence the biasing strip lines have on the antenna performance. But when the length of the sections becomes smaller, more inductors will be needed, which may increase the complexity of the antenna fabrication. Through optimization, a length of 2.2 mm is chosen for the design. The effects of this biasing circuit on the antenna performance will be discussed in Section IV. The possible operating states of the reconfigurable antenna and the corresponding dc biasing voltage states are summarized in Table II. III. SIMULATED AND MEASURED RESULTS Based on the above analysis, an antenna prototype was fabricated and measured. A photograph of the antenna is given in Fig. 4. The PIN diodes are attached to the antenna using electrically conductive silver epoxy. Figs. 5 and 6 show the simulated and measured input reflection coefficients versus frequency for the three operating states of the antenna, respectively. As shown in Fig. 5, the simulated overlapped impedance bandwidth is from


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Fig. 7. Simulated and measured E-plane normalized radiation patterns at 5.0 GHz.

Fig. 4. Photograph of the proposed antenna: (a) whole antenna; (b) balun of the antenna.


Fig. 5. Simulated input reflection coefficients for different states of the antenna.

Fig. 6. Measured input reflection coefficients for different states of the antenna.

5.0 GHz to 5.35 GHz. The measured result given in Fig. 6 is from 5.0 GHz to 5.43 GHz, which agrees reasonably well with

the simulated one. However, it can be noted that there are two resonant frequency points across the operating frequency bands for the measured result of State I, while there is only one for the simulated result. This discrepancy can be mostly attributed to the inaccuracies in the fabrication process and the uncertainties in the discrete component parameters given in the manufacturer’s datasheet. Far-field radiation patterns were measured for the three states of the proposed antenna using a spherical near-field (SNF) antenna measurement system NSI-700S-50 located at CSIRO, Marsfield, NSW, Australia. A NSI-RF-WR159 open-ended rectangular waveguide probe was used as the transmitting antenna. Three dc power supplies were placed inside the chamber and covered with absorbers during the measurement. The orientation of the rectangular coordinate system used in all radiation pattern figures is the same as the one shown in Fig. 3(a). Simulated and measured normalized radiation patterns are compared. Due to the dc biasing lines attached to the antenna, it was difficult to realize a 360 scan of the principle plane. A scan of 180 was conducted during the measurement. Figs. 7, 8, and 9 show the simulated and measured E-plane radiation patterns for the three states at 5.0 GHz, 5.1 GHz, and 5.2 GHz, respectively. It is observed from the above figures that the measured results agree reasonably well with the simulated

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Fig. 10. Measured H-plane normalized radiation patterns at 5.0 GHz.

ones. As seen from Fig. 7–9, the measured main beam for State I are pointed at 0 except for 5.2 GHz where the main beam is towards 2 . The simulated and the measured main beam steering angles for States II and III increase slightly with the operating frequency. For State II, the simulated maximum beam radiations are at 17 , 19 , and 20 for 5.0 GHz, 5.1 GHz and 5.2 GHz, respectively. The measured results show that they are at 20 , 22 , and 19 . For State III, the simulated maximum beam radiations are at , , and for 5.0 GHz, 5.1 GHz and 5.2 GHz, respectively. They are at , , and for the measured results, respectively. It can be noted that the measured sidelobes for States II and III are greater than the simulated ones. This is because the measured beam steering angles are greater than the simulated ones for the above frequency points. The larger the steering angle, the higher the sidelobe level. Also, this discrepancy can be due to the unshielded RF cables and dc biasing lines attached to the antenna, and measurement inaccuracies. As described in Section II, the main beam direction does not change in the H plane for different states of the antenna. In order to clearly show the results, only the measured H-plane radiation patterns for the above frequencies are given. They are displayed in Figs. 10, 11, and 12. It is seen that at each frequency point, the H-plane radiation patterns for different states are similar.



Fig. 13. Measured cross-polarization radiation patterns at 5.0 GHz.

The maximum beam directions for different states are almost at 0 , although slight tilt of the main beam can be observed. The simulated front-to-back ratio of the H-plane radiation pattern is greater than 20 dB, but this is not shown here for the sake of figure clarity. The measured cross-polarization radiation patterns of both E plane and H plane are shown in Figs. 13, 14, and 15 for 5.0 GHz, 5.1 GHz, and 5.2 GHz, respectively. It is seen that


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Fig. 16. Simulated and measured gains of the antenna.


Fig. 17. Impact of the inductive biasing lines on the radiation pattern at 5.1 GHz.

for all the operating states the level of the cross polarization is below 15 dB at the above frequency points. In addition, the simulated and measured realized gains are compared for the three states of the antenna, which are shown in Fig. 16. The measured realized gains for the three states are 7.6–9.03 dBi, 7.5–9.38 dBi, and 8–10.03 dBi, respectively, across the 5.0–5.2 GHz band. It is seen that the gain variation between different states is very small, which is an important feature for pattern reconfigurable antennas. It also can be observed that the measured gains are lower than the simulated ones by a maximum of 2 dB. This can be mainly attributed to the inaccuracy of the modelling of the loss of the PIN diodes due to a lack of available data for the PIN diode operating at 5 GHz and uncertainties in the losses of other discrete elements. Another possible reason for this discrepancy is the measured beam steering angle is larger than that of the simulated one. The larger the tilted angle, the smaller the antenna gain. It is found that the PIN diodes inserted on the balun and the directive strips have effects on the antenna realized gain. The main loss of the PIN diode is the series resistance of 4 when the diode is turned on. Regarding the PIN diodes on the balun, simulation results show that the gains of the antenna for the three states increase by 1.3 dB, 1.2 dB, and, 0.8 dB, respectively at 5.1 GHz when the resistance is reduced to zero. The resistance of the PIN diodes affects less on the gain of State III than those

of the other states. This is because only four PIN diodes are switched on for State III compared to six diodes for the other two states. Similarly, when the resistance of diodes on the directive strips decreases to zero, the simulated gains of the antenna for the three states have an increase of 1.2 dB, 0.4 dB, and 0.6 dB. The reason that PIN diodes bring more losses to State I than the other two states is that two rows of PIN diodes on the directive strips are switched on for State I, but only one row of the diodes are turned on for the other two states. Therefore, there are more losses for State I from the PIN diodes. In order to increase the antenna gain, low loss elements such as radio frequency microelectromechanical system (RF MEMS) switches could be used. In addition, the length of the directive strips and the spacing between them can be optimized to increase the antenna gain further [24]. However, as the goal of the paper is to validate the idea of pattern reconfigurability, we make the directive strips the same length and the spacing between them identical in order to reduce the design complexity. IV. DISCUSSION In order to show the effects of the inductive biasing lines on the antenna performance, the simulated gain patterns of the antenna without the inductive biasing lines for three states at 5.1 GHz are given in Fig. 17 and compared to those with the inductive biasing lines. It is seen that the inductive biasing lines

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have little effect on the antenna radiation patterns. Furthermore, the realized gains remain unchanged for the antenna model with and without the inductive biasing lines. Therefore, the inductive biasing lines are almost transparent to the antenna. It should be noted that the beam scanning can be accomplished by using a butler matrix network [25]. Such an antenna array may use less switches than reconfigurable antennas. However, the antenna size may become greater and the overall losses may be significantly higher which are caused by the switching circuit, the hybrid coupler, and the phase shifters. V. CONCLUSION A novel beam switching quasi-Yagi dipole antenna has been developed. The antenna can direct the E-plane main beam radiation towards three different directions for three operating states, respectively. A measured overlapped impedance bandwidth of 7.7% with a center frequency of 5.2 GHz for the three states is achieved. Compared to most published pattern reconfigurable antennas based on the Yagi-Uda arrays, the proposed antenna employs a new mechanism to reconfigure the main beam direction, which is to change the phase difference of the currents on the two arms of the dipole. Further advantage compared to many reported beam-steering antenna is that a higher gain of 7.5–10 dB for different states across 5.0–5.2 GHz band is obtained. The proposed antenna can find wide applications in advanced communication systems where pattern reconfigurability is used to increase the system capacity and/or link quality. It is particularly suited to low-cost wireless backhauls employing WLAN nodes where beam switching is needed. Moreover, this type of electronically steerable antenna presents a low-cost potential alternative to more expensive phased arrays. Future research includes using varactor diodes to steer the main beam continuously. REFERENCES [1] C. G. Christodoulou, Y. Tawk, S. A. Lane, and S. R. Erwin, “Reconfigurable antennas for wireless and space applications,” Proc. IEEE, vol. 100, no. 7, pp. 2250–2261, Jul. 2012. [2] G. H. Huff and J. T. Bernhard, “Integration of packaged RF MEMS switches with radiation pattern reconfigurable square spiral microstrip antennas,” IEEE Trans. Antennas Propag., vol. 54, no. 54, pp. 464–469, Feb. 2006. [3] S. L. S. Yang and K. M. Luk, “Design a wide-band L-probe patch antenna for pattern reconfigurable or diversity applications,” IEEE Trans. Antennas Propag., vol. 54, no. 2, pp. 433–438, Feb. 2006. [4] S. H. Chen, J. S. Row, and K. L. Wong, “Reconfigurable square-Ring patch antenna with pattern diversity,” IEEE Trans. Antennas Propag., vol. 55, no. 2, pp. 472–475, Feb. 2007. [5] S. J. Wu and T. C. Ma, “A wideband slotted bow-tie antenna with reconfigurable CPW-to slotline transition for pattern diversity,” IEEE Trans. Antennas Propag., vol. 56, no. 2, pp. 327–334, Feb. 2008. [6] Y. Li, Z. Zhang, J. Zheng, Z. Feng, and M. F. Iskander, “Experimental analysis of a wideband pattern diversity antenna with compact reconfigurable CPW-to-slotline transition feed,” IEEE Trans. Antennas Propag., vol. 59, no. 11, pp. 4222–4228, Nov. 2011. [7] S. Nikolaou, R. Bairavasubramanian, C. Lugo, Jr., I. Carrasquillo, D. C. Thompson, G. E. Ponchak, J. Papapolymerou, and M. M. Tentzeris, “Pattern and frequency reconfigurable annular slot antenna using PIN diodes,” IEEE Trans. Antennas Propag., vol. 54, no. 2, pp. 439–448, Feb. 2006.

[8] S. Yong and J. T. Bernhard, “A pattern reconfigurable null scanning antenna,” IEEE Trans. Antennas Propag., vol. 60, no. 10, pp. 4538–4544, Oct. 2012. [9] M.-I. Lai, T.-Y. Wu, J.-C. Wang, C.-H. Wang, and S. Jeng, “Compact switched-beam antenna employing a four-element slot antenna array for digital home applications,” IEEE Trans. Antennas Propag., vol. 56, no. 9, pp. 2929–2936, Sep. 2008. [10] C. W. Jung, M. Lee, G. P. Li, and F. D. Flaviis, “Reconfigurable scan-beam single-arm spiral antenna integrated with RF-MEMS switches,” IEEE Trans. Antennas Propag., vol. 54, no. 2, pp. 455–463, Feb. 2006. [11] G. H. Huff, J. Feng, S. Zhang, and J. T. Bernhard, “A novel radiation pattern and frequency reconfigurable single turn square spiral microstrip antenna,” IEEE Microw. Wireless Compon. Lett., vol. 13, pp. 57–59, Feb. 2003. [12] S. V. S. Nair and M. J. Ammann, “Reconfigurable antenna with elevation and azimuth beam switching,” IEEE Antennas Wireless Propag. Lett., vol. 9, pp. 367–370, 2007. [13] S. Zhang, G. H. Huff, J. Feng, and J. T. Bernhard, “A pattern reconfigurable microstrip parasitic array,” IEEE Trans. Antennas Propag., vol. 52, no. 10, pp. 2773–2776, Oct. 2004. [14] X.-S. Yang, B.-Z. Wang, W. Wu, and S. Xiao, “Yagi patch antenna with dual-band and pattern reconfigurable characteristics,” IEEE Antennas Wireless Propag. Lett., vol. 6, pp. 168–171, 2007. [15] M. Donelli, R. Azaro, L. Fimognari, and A. Massa, “A planar electronically reconfigurable Wi-Fi band antenna based on a parasitic microstrip structure,” IEEE Antennas Wireless Propag. Lett., vol. 6, pp. 623–626, 2007. [16] S. Lim and H. Ling, “Design of electrically small pattern reconfigurable Yagi antenna,” Electron. Lett., vol. 43, no. 24, pp. 1326–1327, Nov. 2007. [17] D. Rodrigo, L. Jofre, and B. A. Cetiner, “Circular beam-steering reconfigurable antenna with liquid metal parasitic,” IEEE Trans. Antennas Propag., vol. 60, no. 4, pp. 1796–1802, Apr. 2012. [18] R. Guzman-Quiros, J. L. Gomez-Tornero, A. R. Weily, and Y. J. Guo, “Electronically steerable 1-D Fabry-Perot leaky-wave antenna employing a tunable high impedance surface,” IEEE Trans. Antennas Propag., vol. 60, no. 11, pp. 5046–5055, Nov. 2012. [19] P.-Y. Qin, C. Ding, and Y. J. Guo, “A high-gain beam-steering quasi-Yagi antenna,” in Proc. Int. Symp. on Antennas and Propagation, Japan, Nov. 2012. [20] W. R. Deal, N. Kaneda, J. Sor, Y. Qian, and T. Itoh, “A new quasi-Yagi antenna for planar active antenna arrays,” IEEE Trans. Microw. Theory Tech., vol. 48, no. 6, pp. 910–918, Jun. 2000. [21] C. A. Balanis, Antenna Theory: Analysis and Design, 3rd ed. New York: Wiley, 2005. [22] CST Studio Suit 2012. Computer Simulation Technology, Darmstadt, Germany. [23] M/A-COM datasheet for MA4FCP300. [24] E. A. Jones and W. T. Joines, “Design of Yagi-Uda antennas using genetic algorithms,” IEEE Trans. Antennas Propag., vol. 45, no. 9, pp. 1386–1392, Sep. 1997. [25] C.-H. Tseng, C.-J. Chen, and T.-H. Chu, “A low-cost 60-GHz switched-beam patch antenna array with butler matrix network,” IEEE Antennas Wireless Propag. Lett., vol. 7, pp. 432–435, 2008.

Pei-Yuan Qin (M’13) was born in Liaoning Province, China, in 1983. He received the Bachelor degree in electronic engineering from Xidian University, Xi’an, China, in 2006, and a joint Ph.D. degree from Xidian University, China and Macquarie University, Australia, in electromagnetic fields and microwave technology in 2012. He is currently a Postdoctoral Research Fellow in Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia. His research interests are in the areas of reconfigurable antennas, phase shifters, reconfigurable reflectarrays, and MIMO communications. Dr. Qin was a recipient of an international Macquarie University research excellence scholarship and was awarded the Vice-Chancellor’s commendation for academic excellence by Macquarie University.


Y. Jay Guo (SM’96) received the Bachelor degree and a Master degree from Xidian University, China, in 1982 and 1984, respectively, and the Ph.D. degree from Xian Jiaotong University, China, in 1987. He has been with CSIRO since 2005, managing a number of portfolios of research programs including smart and secure infrastructure, broadband networks and services, Broadband for Australia and Safeguarding Australia. From August 2005 to January 2010, he served as the Research Director of the Wireless Technologies Laboratory in CSIRO ICT Centre. Prior to joining CSIRO, he held various senior positions in Fujitsu, Siemens and NEC in the U.K. He is an Adjunct Professor at University of New South Wales, Macquarie University, University of Canberra, all in Australia, and a Guest Professor at the Chinese Academy of Science (CAS) and Shanghai Jiaotong University. His research interest includes reconfigurable antennas and radio systems, antenna arrays, wireless positioning and multi-gigabit wireless communications. He has published three technical books, 88 journal papers and 130 refereed international conference papers, and holds 18 patents. Dr. Guo is a Fellow of the IET. He is the recipient of 2012 Australian Government Engineering Innovation Award, 2007 Australian Engineering Excellence Award, 2007 and 2012 CSIRO Chairman’s Medal and 2012 CSIRO Newton Turner Award. He has chaired numerous international conferences. He is General Chair of ISAP2015, IWAT2014, Patronage and Publicity Chair of IEEE ICC2014, TPC Chair of 2010 IEEE WCNC, and TPC Chair of 2007 and 2012 IEEE ISCIT. He has been the Executive Chair of Australia China ICT Summit since 2009. He served as Guest Editor of the IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION Special Issue on “Antennas and Propagation Aspects of 60–90 GHz Wireless Communications” and the “IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS Special Issue on “Communications Challenges and Dynamics for Unmanned Autonomous Vehicles.”

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Can Ding (S’10) was born in Anhui Province, China, in 1989. He received the B.S. degree in micro-electronics from Xidian University, Xi’an, China, in 2009, and is working towards the Ph.D. degree at CSIRO, Australia, as a joint Ph. D. student from Xidian University. His research interests are in the areas of reconfigurable antennas and microwave circuit design.