# Design of a Tri-Band Wearable Antenna for Millimeter-Wave 5G Applications
## 1 Introduction  
The increase in the number of users will cause a need for new communication systems with high data rates, low costs, efficiency, and simplicity [1]. A viable choice for these systems is the fifth generation (5G) of communication technology [2, 3]. The 28 GHz and 38 GHz millimeter-wave (mm-wave) frequency bands are promising for 5G wireless communication because of the low absorption rate and minimal error for both line of sight (LOS) and non-line of sight (NLOS) systems [4, 5, 6]. For satellite communication systems, the 60 GHz V-band is a suitable frequency range along with Wi-Fi. At 5G mm-wave frequencies, an antenna's geometrical structure and small size play a critical role in the communication system. Antennas for 5G must also have high gain and efficiency due to increased air absorption and attenuations [7, 8, 9]. However, the 5G antenna's strong gain is compromised due to its compact size. Consequently, an antenna with strong radiation properties is required for the 28 GHz, 38 GHz, and 60 GHz millimeter-wave frequency bands. Much research was carried out recently on mm-wave frequency for single, dual, or multiband operation [10; 11; 12; 13; 14; 15; 16; 17; 18; 19]. The wire-bond antenna for V-band applications was presented in [10] with a circularly polarized capability. It was small and capable of transmitting from 51 GHz to the upper end of the frequency range. However, the proposed antenna has a complex geometrical structure and low gain (0.8 dBi). Another V-band mm-wave antenna was proposed to achieve a high gain of 14 dBi and a broad bandwidth of 57 GHz to 66 GHz [11]. Though the proposed antenna has high gain although it is large in size. A mm-wave microstrip fed antenna with a single resonant band between 34.1 and 38.9 GHz is described in [12]. Directivity values ranged from 6 dBi to 8 dBi for single antenna setup and parasitic patches, respectively, in the given structure. A tri-band antenna for 5G mm-wave applications was proposed in another paper [13]. On the first layer, microstrip feed is provided, and on the second, proximity-linked parasitic patches are used. At a maximal gain of 5.66 dBi, this antenna resonantly resonates at 45.3, 55.7, and 66 GHz. Similarly, [14] presents a mm-wave communication system triple band antenna with a very basic configuration. With very limited impedance bandwidth, this antenna achieved peak gains of 6.5, 7, and 5 dBi, respectively, at 24 GHz, 28 GHz, and 38 GHz. As another example of an inset feed, a three-band slotted millimeter-wave antenna was published [15]. The antenna has a maximum gain of 6.3 dBi across the resonant bands. Other research [16] proposed a dual-band mm-wave antenna for 5G communication systems operating at 28 GHz and 38 GHz. In terms of peak gain, the antenna covers the 26.65-29.2 GHz and 36.95-39.05 GHz bands, respectively, with a peak gain of 1.27 dBi and 1.83 dBi. A high-gain dual-band antenna described in [17] may operate at 28 and 38 gigahertz. The antenna, on the other hand, has a huge substrate. Ref. [18] presents an antenna design for 28/38 GHz 5G mm-wave frequencies with a T-shaped dual band antenna and a triangular-shaped slot on the bottom layer for antenna performance optimization. This highest gain of 5.75 and 7.23 dBi, respectively, is seen at 28 and 38 gigahertz [19]. A new microwave and mm-wave multiband triangular patch antenna is described. In order to cover the 23-28 GHz band, this antenna has an overall gain of 5.85 dB, although its total size is rather huge. At mm-wave frequencies, researchers have an enormous difficulty in constructing low-profile [20] and small antennas that have broad bandwidth, high gain, and multiband properties. A low-profile, tri-band, high gain monopole antenna for 28 GHz, 38 GHz, and 60 GHz mm-wave frequency bands is discussed in this research, considering the previously described difficulties and constraints. Monopole antennas [21] were chosen for this project because of their many advantages, including their small size, low profile, and simple geometry.