## 1 Introduction  
Non-terrestrial networks (NTN) are an effective solution for providing wireless communication services to areas that are either uncovered or under-served [1; 2; 3]. This communication platform facilitates the interconnection of devices across diverse locations encompassing the skies, seas, and even space, employing various vehicles such as satellites, aircraft, and ships. Notably, the utilization of unmanned aerial vehicles (UAVs) as flying wireless base stations enables the establishment of aerial wireless networks, leading to a wealth of pertinent research in this domain [4; 5; 6; 7]. UAVs already play substantial roles across many fields including agriculture, inspection, aerial photography, surveillance, and logistics [8; 9]. Through the integration of millimeter wave (mmWave) or terahertz wireless transceivers, UAVs hold the potential of connecting them through exceptionally high-speed wireless channels [10]. This advancement is anticipated to pave the way for the realization of aerial networks with unprecedented data transfer capabilities. Within the mmWave and terahertz spectrum, the use of highly directional antennas is common practice to counterbalance the substantial propagation loss compared to con ventional microwave bands [11; 12]. Consequently, communication under these bands is confined to spatially restricted, spot-like communication zones. When transceivers are mounted on vehicles, including UAVs, the positions of these ultra-narrow zones undergo rapid changes, thereby limiting the available temporal and spatial windows for communication. Therefore, it becomes significant to efficiently exploit the opportunities presented by these ultra-narrow spots offering high-speed communication services. Addressing the distinctive attributes of mmWave and terahertz frequencies, extensive research has been dedicated to the development of beam tracking techniques utilizing active phased array antennas [13; 14; 15]. However, these array antennas encounter challenges as the frequency escalates, exemplified by control complexity and an increase in system cost [16]. In most of these previous studies, air-to-air wireless data transmission between UAVs was limited to theoretical considerations, with few experimental demonstrations. Figure 1 illustrates our concept of a UAV wireless network using proximity opportunities, relying solely on their autonomous navigation ability. Within the context of a drone traffic framework analogous to a drone highway [17], where UAVs densely populate designated airways, UAVs planning routes to various destinations exploit instant proximity opportunities to enable the exchange of high-capacity data. Moreover, UAVs traveling in the same direction engage in continuous data transmission by keeping their proximity. We envision this networking paradigm as the foundation for establishing a wireless data relay network, based on device-to-device (D2D) communications or ad hoc networks, leveraging the dense presence of UAVs within a designated flight zone. The realization of this data relay network, powered by UAVs, requires a comprehensive understanding of the distinct transmission characteristics that emerge with the integration of mmWave or terahertz technologies onto UAV platforms. This paper explores the viability of utilizing ultra-narrow spot for mmWave or terahertz communications, even without the use of active beam control techniques like beam tracking. The primary contributions of this paper are the following:  
* Clarification of the attributes of ultra-narrow spot and its issue in the context of frequencies beyond mmWave;
* Presentation of the static data transfer characteristics within the 60 GHz band communication while UAVs are hovering;  
Figure 1: Illustration of mmWave and terahertz communications within a UAV-based network. Two data transfer methods are depicted: instantaneous proximity communications involving UAVs passing each other, and continuous communications wherein UAVs maintain formation.