0018-926X (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TAP.2018.2860118, IEEE Transactions on Antennas and Propagation IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION A Novel Reconfigurable Microstrip Patch Antenna with Polarization Agility in Two Switchable Frequency Bands Rajesh Kumar Singh, Ananjan Basu, and Shiban Kishen Koul Abstract— A novel reconfigurable microstrip-fed patch antenna with polarization agility in either of two bands is proposed in this communication. Frequency reconfigurability is achieved by connecting an additional small patch to the main patch through a PIN diode. Each corner is cut off from the main patch through a narrow L-shaped cut to get polarization reconfigurability. Additionally, the impedance and axial ratio bandwidths are enhanced by using the proximity coupled feed. Both prototypes are designed, fabricated and tested. The measured results agree well with the simulated results in all cases. Also, the proposed microstrip- fed antenna is tested at high RF input power. The proposed structures are simple, low profile, low cost and have simple bias circuitry. The proposed antennas are capable of operating in three polarization states, i.e., left hand circular polarization (LHCP), linear polarization (LP), and right hand circular polarization (RHCP) in two frequency bands. The proposed structures are best suited for modern advanced wireless communication systems such as LTE, and 5G. Index Terms— Circular and linear polarization, patch antenna, PIN diode, reconfigurability, truncated corner. I. INTRODUCTION Reconfigurable microstrip patch antennas are widely used in the current wireless communication systems due to their planar structure, low profile, low cost, light weight and ease of fabrication. Switches are placed in the structure to change the radiator shape, by which the radiation from the patch is controlled and hence reconfigurability is achieved. Many modern communication system applications require different frequency bands with different polarization characteristics. Multifunction antennas have received a lot of attention in recent times, because these antennas can provide multiple services and cover various frequency bands with different radiation characteristics. However, the use of carrier aggregation (CA) has been proposed in modern wireless systems such as LTE, and 5G. In CA, a device can transmit or receive on several channels simultaneously for increased data rate. The used channels can also exist within the same frequency band (intraband CA) or in separate bands (interband CA). To accommodate more channels, more bandwidth is required in the whole band. Additionally, the reliability and power handling capacity of the system must be tested at high RF power. A conventional rectangular microstrip patch antenna radiates a linearly polarized wave. To get circular polarization (CP), two orthogonal modes should be excited with the same amplitude and phase difference of 90°. This can be achieved by perturbing the original shape of the radiator by inserting some slits [1] or slots [2] of various shapes, or truncating the corners [3], [4], [5]. A detailed study of polarization switchable antennas has been given in [6]. R. K. Singh is with the Bharti School of Telecommunication Technology and Management, Indian Institute of Technology Delhi, New Delhi 110016, India. (e-mail: rajeshsingh.iitd@gmail.com). A. Basu and S. K. Koul are with the Centre for Applied Research in Electronics, Indian Institute of Technology Delhi, New Delhi 110016, India (e-mail: ananjan_b@yahoo.com; shiban_koul@hotmail.com). Color versions of one or more of the figures in this communication are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2016.xxx Various polarization reconfigurable antennas have been published recently. Dual-band polarization-agile antennas have been reported in [7], [8], and some combined reconfigurable antennas have been presented in [9]-[15]. The antennas reported in [12]-[15] are tunable over a wideband and show good axial ratio and impedance matching within the whole band, but the ARBW is less in each tuning band. In [13], the ARBW is good but the antenna is large. A novel reconfigurable corner truncated microstrip patch antenna with polarization reconfigurability in two switchable frequency bands is proposed in this communication. Seven PIN diodes are employed in the circuit to achieve three polarization states in two switchable frequency bands. The proposed antenna is fabricated on N9000 Neltec substrate with relative dielectric constant of 2.2, substrate height of 0.762 mm, and loss tangent of 0.0009. The operating frequency of the antenna can be switched between two bands (5.2 and 5.7 GHz). The fractional axial ratio bandwidth of the proposed antenna is more than 1.11 % in the lower band and 0.56 % in the higher band. The impedance bandwidths (IMBWs) and axial ratio bandwidths (ARBWs) are enhanced by using proximity coupled feed. The measured axial ratio bandwidths are more than 2.57% and 1.61 % in the lower and higher band, respectively. The proximity coupled antenna has two switchable bands with centre frequencies of 5.28 and 6.1 GHz. Also, the microstrip-fed antenna is tested at high RF power. A good agreement between simulated and measured results is obtained. The communication is arranged as follows. Section II presents the design procedure and operating principle of the proposed antenna. Section III discusses the measured results and compares with the simulated results. The enhancement in the ARBWs and IMBWs are demonstrated in Section IV and the performance of the antenna is tested at high RF input power. Finally, the paper is concluded by giving some applications of the proposed work. II. ANTENNA DESIGN AND OPERATING PRINCIPLE A. Reconfigurable antenna design To design a reconfigurable microstrip patch antenna with polarization reconfigurability in two switchable bands, a conventional patch antenna at operating frequency of 5.2 GHz is designed first by using standard formulas given in [16]. An additional small patch is then connected to the main patch. With this additional patch, the frequency can be increased or decreased from the reference frequency. This frequency shift depends on various parameters such as The length and width of the additional patch, the gap between the main and additional patch, and the position of the switch placed between them. Parametric analysis is done by varying these parameters and simulated in CST Microwave Studio [17]. A noticeable change in frequency is observed by varying the width of the additional patch. 0018-926X © 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.