## 1 Introduction  
The demand for maximized screen sizes has gathered great importance for smartphone industries. This requirement is particularly urgent for millimeter-wave fifth generation (5G) communications, as soaring data throughput is associated with high-resolution applications. A perfect full-screen display device, which employs the entire front panel as a screen, is a game danger for screen maximization purposes; however, this technology has not yet been developed due to the unoccupied area necessary for the mobile antennas. As a touchscreen consists of transparent conductive coating layers, the touchscreen and a printed circuit board (PCB) are constructed as parallel conductive plates. Antennas cannot create radiation unless the touchscreen is demetalized. Thus, smartphones currently notch the screen display for the antenna arrangement.  
In fact, the influence of the conductive surface of a touchscreen has not been given the attention it needs, even though there has been a dramatic proliferation in research on millimeter-wave 5G handset antennas. The antenna performance from recent studies concerning millimeter-wave 5G handsets is provided in Table 1[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22]. To create millimeter-wave 5G antenna arrays, these earlier studies employed substrate-integrated-waveguide (SIW) structures [1, 8], patches [2, 4, 6, 22], monopoles along with slots [3], cavity-backed slots [5, 7, 11, 12, 14, 15, 18], dielectric resonators [9], embedded structures in a fourth generation (4G) structure [10, 13, 19], snowflake monopoles [16], quasi-Yagi structures [17], and ring resonators [21]. This academic research has attempted to enhance antenna performance in terms of miniaturization, bandwidths, gain, and isolation, but few studies have developed antennas to suit a large area for the conductive touchscreen [14; 21]. Developing an antenna for a conductive full-screen display must address two challenges. First, the environment of parallel conductive plates makes it difficult to enhance the bandwidth and gain of the antennas. Second, the smartphone is required to deploy an antenna for a wireless local area network (WLAN) at 2.45 GHz, but designing a WLAN antenna to suit parallel conductive plates is more difficult than a millimeter-wave antenna due to its larger dimensions.  
The purpose of this study was to move mobile antenna development from an ideal PCB environment to a conductive touchscreen device with a maximized screen size. Three antenna modules were integrated in a perfect full-screen display smartphone, the front and back of which were fully coated with copper. The three antenna modules included a 1 \(\times\) 12 patch array at 28 GHz, a 1 \(\times\) 8 patch array at 38 GHz, and a loop antenna at 2.45 GHz. These frequencies follow the standards for 5G and WLAN. In particular, the 3 rd Generation Partnership Project (3 GPP) regulates 5G New Radio (NR) Frequency Ranges 2 (FR2) for data throughput up to 12 Gbps, where n257, n260, and n261 utilize 26.5-29.5 GHz, 37.0-40.0 GHz, and 27.5-28.4 GHz, respectively. All three are fully covered by the proposed antennas with impedance bandwidths of 26.5-32.0 GHz and 35.2-42.0 GHz. Additionally, the proposed WLAN antenna meets the IEEE 802.11g standard. The performance of the proposed antennas is summarized in Table 1. Although the design space included parallel conductive plates, superior performance including sufficient bandwidths, high isolation, and high gains were achieved. The antenna design, analysis, and the results will be presented in the following sections.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Impedance** & \multirow{2}{*}{**Number of** **Elements**} & **Isolation** & **Peak Gain** & **Proportion of** **Metallic Area on** \\  & **Bandwidth** & & **(GHz)** & **(dB)** & **(dBi)** & **Screen (\%)** \\ \hline
[1] & 26.5–29.4 & 8 & 20.0 & 14.0 & 0 \\
[2] & 34.2–38.8 & 1 & N.A. & 5.7 & 0 \\
[3] & 26.0–28.4 & 8 & N.A. &