## 1 Introduction  
Wireless communication has been developed and accepted in industries building the infrastructure of cities and in profit-making areas. For example, it makes cellular networks possible on a regional scale and allows satellite links to happen on a global scale. From its first generation to the present day, it has been evaluated to meet the industrial standard or public demands, and it has been tailored to comply with certain requirements, such as connectivity to nodes of the network and high data transmission rates. These are being realized and put into more use in the 5G mobile service era through larger bandwidths and low-latency millimeter-wave (henceforth, mmW) wireless systems [1; 2]. Even in the 5G era's infancy, scholars have begun talking about 6G, which might confuse people with presumption that 5G has been skipped. However, the two paradigms have a lot of expectations in common. In accordance with white papers and books on standards that 3 GPP and mobile carriers have published, software and hardware for the 5G are to be also used for the 6G. What differentiates 6G from 5G, aside from the fusion of separate functions, are the three-dimensional communication topologies interconnecting the ground networks with the wireless signal flows to satellites. The vertical paths will be accessed by the horizontal networks that are conventionally limited in expanding the coverage and raising the speed, but the 3D network diagram is drawn and schematized between the caller and receiver in order to find possible routes and estimate the costs, and to make the suggestion that an optimized route leads to a cost-saving solution of fast data exchange. While this non-terrestrial networking (NTN) is being studied and worked on very actively,the fusion of separate functions is examined in terms of its merits and hurdles as another feature of 6G. The fusion of technologies from different fields is exemplified by sensing and communication. This is so called integrated sensing and communication or ISAC. Not only 6G but also other communication sectors, like satellite links, have combined one technology with another. The SAR satellite is equipped with communication payload-neighboring RF sensors to collect the data of reflected waves from the Earth. Primarily, as more and more functions and their hardware blocks are demanded for wireless communication, and the size of the wireless terminal is limited as a result of users' preference, integration of different functions is required. Secondarily, shortcomings of two functional blocks can be improved by mixing them after they are juxtaposed to find points to compensate for. A sensor can use the mmW communication channel to tell its status to the controller. The beamforming antenna of the communication system takes the information on the direction of the infra or nomad in the IoT network that a sensor generates. The information is not polluted much by noise because the frequency of the sensor differs from that of the communication device. ISAC is introduced with a great number of use-cases. One of them is a vehicle having the array antenna as the communication device and autonomous radar as the sensor. Another is the LEO satellite, which is connected to the ground by the communication channel and refers to the location data received by the sensor from the surface. It is worth checking what is presented in the selected literature and reports on the ISAC and its antenna technologies. ISAC can be depicted in various ways but is embodied from the viewpoint of waves from antennas mounted on vehicles to allow dual-capability as follows. Even if ISAC has been recently coined, there have been techniques to place sensing and communication devices together on a platform, as shown in Figure 1. Whether separated or integrated, modern automobiles are expected to carry out functions of wireless communication under GSM, WiFi, and LTE-A protocols and RF sensing for collision avoidance.