# Antennas for Licensed Shared Access in 5G Communications with LTE Mid- and High-Band Coverage
## 1 Introduction  
The rapidly growing demands of mobile traffic can be supported by fifth-generation (5G) wireless communication systems [1; 2; 3; 4; 5; 6]. An application of cognitive radio technology named licensed shared access (LSA) has been proposed for 5G mobile communication systems to allow the sharing of spectrum among mobile network operators [7; 8; 9; 10]. In Europe, a 1.5 GHz band (1452-1492 MHz) and a 2.3 GHz band (2300-2400 MHz) have been allocated for LSA service. The proposed LSA service has been tested in the 2.3 GHz band in Europe and more bands are expected to be allocated in the future [8; 11; 12]. Antennas with very large bandwidths are required in mobile devices to cover many bands, including, for example, the long-term evolution (LTE) mid (1427-2690 MHz) band, LTE high (3400-3800 MHz) band, DCS/GSM1800, and PCS/GSM1900 bands. The LTE mid and high bands consist of 16 frequency-division duplexing (FDD) bands (LTE 1-4, 7, 9-11, 15, 16, 21; 22; 23; 24; 25; 30) and 11 time-division duplexing (TDD) bands (LTE 33-43) [13]. Several antennas have been proposed with multiband or wideband operation for wireless wide-area network (WWAN)/LTE hand-held devices to cover the frequency range from 1710 to 2690 MHz [14; 15; 16; 17; 18]. The antenna presented in [19] covers a wide frequency band from 1585 to 2195 MHz. However, this antenna covers only a part of the LTE mid band, and the performance of the antenna has not been verified after integrating the antenna into the substrate of a mobile phone. On the other hand, metal-framed antennas are reported in [20; 21]. The antenna in [21] covers only the LTE mid band, whereas the antenna in [20] covers both the LTE mid and high bands. Some antennas have been reported to cover both the 1710-2690 MHz (LTE mid) and 3400-3800 MHz (LTE high) frequency ranges [22; 23; 24; 25; 26]. Recently, an antenna was presented in [27] that covers both frequency bands. However, in order to achieve acceptable impedance matching (\(|S_{11}|<-6\) dB) in the above-mentionedbands, an extra lumped-element-based circuit is required with the feed section. The reported antennas cover 13 FDD and all TDD LTE bands. For example, the maximum antenna coverage reported in [17; 24; 28] is 1630-2740 and 3300-3800 MHz. Though the antenna presented in [28] is compact and covers the 1555-2690 and 3100-3700 MHz frequency bands, three nulls have been observed in the high-band radiation patterns. Moreover, it does not cover the entire high band. Mobile hand-held antennas that can cover the following FDD-LTE bands are in high demand: LTE11 (1427-1501 MHz), LTE21 (1447-1511 MHz), and LTE24 (1525-1661 MHz). The LTE11 and LTE21 bands have been deployed in Japan by 'au mobile' and 'NTT Docomo', respectively, and the LTE24 band in the USA by 'Ligado Networks' [29; 30]. Therefore, mobile devices require antennas to cover the 0.69-0.96, 1.42-2.69, and 3.3-3.8 GHz frequency bands without any nulls in the radiation patterns in all bands. Moreover, these antennas should be compact enough to fit in a mobile device while allowing enough space for other electronic circuits and the battery. For presentation simplicity, the above three bands are referred to as the low, mid, and high bands, respectively, throughout this paper. Several reported antennas have sufficiently wide operating bandwidths to cover the low band [14; 15; 16; 17; 22; 23; 24; 25]. Considering the requirements of current and forthcoming mobile communication systems, we aimed to design antennas to cover the mid and high bands while maintaining an antenna area and ground clearance similar to the antennas reported in [14; 15; 16; 17; 22; 23; 24; 25]. In this paper, first, a planar antenna is presented for hand-held devices to cover the LSA frequency bands. Later, two novel antenna designs are described. One is a dual-band antenna with a planar structure loaded with an I-shaped vertical plate, and the other is a wideband antenna with a planar structure loaded with an L-shaped vertical plate.