Regular paper Low-profile tunable multi-band LTE antennas with series and shunt tuning devices Abdullah J. Alazemi a,⇑ , Bilgehan Avser b , Gabriel M. Rebeiz b a Faculty of Engineering and Petroleum, Department of Electrical Engineering, Kuwait University, Safat, Kuwait b Faculty of Engineering, Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA 92093, USA article info Article history: Received 19 June 2019 Accepted 31 July 2019 Keywords: Planar inverted F-antennas (PIFAs) Tunable antennas Long-term evolution frequency range (LTE) Mobile antennas Carrier aggregation RF-MEMS Data-rate Varactor diode abstract This paper presents two tunable three-feed triple-band antennas using series or shunt tuning devices. The paper includes a theoretical analysis in the effects of the series and shunt tuning devices on antenna size and performance. Each antenna has three feeds to cover three bands within the long-term evolution (LTE) frequency range (0.7–2.7 GHz). Each antenna operating frequency is independently tunable by a varactor diode (series or shunt). The antennas are well matched at all feeds (S 11 -S 33 < À10 dB) and the isolation between the feeds is <À20 dB in most cases. The antenna volume is 66 Â 100 Â 3.15 mm 3 and is placed on RO4003C (e r = 3.55) printed-circuit board (PCB). Radiation patterns and antenna effi- ciency are measured inside a Satimo chamber and the results agree well with the simulations. This paper shows the first comparison between series and shunt tuning devices on small antennas. Application areas include cellular communications, carrier aggregation, and advanced multiband systems. Ó 2019 Elsevier GmbH. All rights reserved. 1. Introduction With the rapid growth in wireless communications, the need for high-speed data rates in mobile applications has been increas- ing in the past two decades. As an essential part of a wireless sys- tem, antennas are required to support multiple standards in mobile handsets [1–21]. Carrier aggregation, as a major feature of advanced long term evolution (LTE-Advanced) allows to com- bine a number of separate LTE carriers to transmit or receive data which results in high communication bandwidth and faster data rates (up to 1 Gbps/s) [1–3]. The implementation of carrier aggre- gation may require the wireless carrier to use different frequency bands. Therefore, a tunable multiband antenna is desirable for Multiple-Input-Multiple-Output (MIMO) and carrier aggregation applications. Many technical solutions for multiband antennas have been used in mobile platforms [4–21]. In particular, multiband antennas based on planar inverted-F antenna (PIFA) are very attractive due to PIFA compact-size, conformal structure, and multifunctional capabilities. Multiband operation was achieved with etched slots in the radiating element [4–10], by RF-traps [11], or by different resonance paths [12]. The PIFA antenna can also be loaded with external devices such as PIN diodes, varactor diodes, or RF-MEMS [13–20]. Those devices do not require extra area and are used to provide the antenna with frequency tuning operation or force the antenna to resonate at several operating frequencies achieving a wideband performance. A reconfigurable multi-band PIFA is obtained by adjusting the on/off state of the PIN diode [13,14], or by implanting RF-MEMS switches for high-linear performance [15–17]. Recently, varactor diodes are popularly used to design multi- band tunable/reconfigurable antennas due to their well- performing DC voltage control and continuity properties. The var- actor diode is attached to the antenna structure and tunes its res- onant frequency. This includes single-feed dual-band antennas with two resonant frequencies [18], dual-feed dual-band antennas with two resonant frequencies [19]. The single-feed single-band antenna can be attached with two (or more) varactor diodes to introduce more resonant frequencies in the same band [20,21]. This paper presents two tunable antennas with three-feed structure and triple-resonance, covering the low-band (0.7– 1 GHz), the mid-band (1.6–2.2 GHz), and the high-band (2.2– 2.7 GHz) of LTE frequency bands as shown in Fig. 1. The first antenna is loaded with a series tuning device (varactor diode) to tune its operating frequency while the second antenna is loaded with a shunt tuning device. The three resonant frequencies are independently tunable within their frequency band. The paper https://doi.org/10.1016/j.aeue.2019.152855 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved. ⇑ Corresponding author. E-mail address: aalazemi.ku@gmail.com (A.J. Alazemi). Int. J. Electron. Commun. (AEÜ) 110 (2019) 152855 Contents lists available at ScienceDirect International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue