# Crescent Microstrip Antenna for LTE-U and 5G Systems
## 1 Introduction  
Radio communication and wireless technologies are an integral part of the functioning of today's societies. Everyday communication, from calling home from a mobile phone to advanced medical applications such as monitoring and diagnostic solutions, all use wireless technologies for communication. The field of wireless cellular network technology has seen a significant development in recent years, allowing the emergence of many new applications in addition to the traditional mobile phone calls. The 3G and 4G data transmission standards have transformed cellular telephony and available wireless services. We are currently at the stage of implementing the 5G system, which is replacing the earlier technologies on the market. At the same time, the development of cellular technologies and wireless local area networks (WLAN), operating on the basis of the IEEE 802.11\(\times\) (Wi-Fi) standards, are rapidly spreading. Currently, these systems offer bitrates much higher than cellular telephone systems. At the same time, the number of access points (hotspots) that offer the ability to connect to the network is constantly growing. The desire to use the advantages of both mobile telephony and wireless local networks led to the idea of integrating the currently used communication systems in one device. The future of telecommunications will belong to solutions that can flexibly adapt to changing technical and geographical conditions [1, 2]. These systems are commonly used in cell phones that must support all of these radio systems simultaneously. A mobile telephone or smartphone must ensure that all radio systems that it supports are compatible. Currently, we use the 3G system on our phone or smartphone, which is called the \"third-generation cellular\" system. This standard enables the use of multimedia, video calls, and mobile internet. Another system used in smartphones is the 4G LTE (long-term evolution) system. This is the first significant improvement in the area of mobile telecommunications networks. The LTE standard ensured broadband internet access, fast data transfer, and a wide range of mobile services, including watching movies in HD quality. The 5G system is increasingly used in smartphones. It is the fifth generation of cellular networks, which is a significant step forward compared to the currently used 4G LTE networks. The 5G system enables data transfer speeds down to Gbps and offers a significantly greater bandwidth and short connection delays. The 5G networks are designed keeping in mind the rapid growth of data volumes and communication in modern societies, the Internet of Things, with billions of interconnected devices, and future innovations [3; 4; 5]. Mobile networks send and receive low-intensity radio signals. They are sent and received by antennas linked to radio devices (transmitters and receivers) known as cellular base transceiver stations. The base stations are connected to other mobile and fixed networks to which they transmit signals/calls. The dissemination of 5G networks requires the preparation of antenna infrastructure and the implementation of new technological solutions. A significant number of antennas (apart from mobile devices) will be installed inside buildings, especially inside public utility buildings, including stadiums, railway stations, and shopping centers. This fact shows how important an element a well-designed antenna is in radio systems, and therefore it should be given a lot of attention during designing a radio system [1; 2]. This article presents the proposed model of a two-band microstrip antenna made in the CST Microwave Studio software, for which the main assumption is its operating frequencies in the LTE-U band and one of the 5G system bands. Other important assumptions for the antenna model are its small size (not to be larger than 60 mm \(\times\) 60 mm) and elliptical polarization.