## 1 Introduction  
Over the past two decades, air-to-ground (A2G) communications, particularly between unmanned aerial vehicle (UAV) and ground systems, have received considerable attention. Compared to terrestrial base stations, A2G communications via UAVs offer flexible deployment and extended coverage, as UAV-based aerial base stations can be promptly deployed to regions that terrestrial base stations may not be able to cover. Particularly, the fixed-wing UAV has longer flight endurance and larger overload that enables coverage enhancement and network optimization of terrestrial-based communication systems [1]. As such, UAV has been widely considered as a vital platform for aerial base stations in beyond Fifth Generation (B5G) communication [2, 3]. Commercial technologies such as Fourth Generation (4G) Long Term Evolution (LTE), Fifth-Generation NewRadio 5G NR, Wi-Fi, and millimeter wave are capable of supporting the A2G communication link transmission. For instance, Wi-Fi 5 (802.11 ac) and Wi-Fi 6 (802.11 ax) can provide convenient and high-speed connection options for UAV operations and data transmission over short distances. Additionally, organizations such as the International Telecommunication Union (ITU), Unmanned Aircraft Systems International Association (UASIA), and the Federal Aviation Administration (FAA) in the United States have initiated multiple research projects to establish international standards and regulations for UAV communications. These standards and regulations primarily address the communication technologies, protocols, and spectrum usage of UAVs. Particularly, the frequency band allocated to A2G communications varies by countries and regions, where the band at 2.4 GHz is widely adopted for remote control and data transmission in small-sized UAVs. Other frequency bands, such as L- and C-bands, are also considered in A2G communication for specific demands. Accurate knowledge on the A2G wireless channel is of great importance to facilitate the development of UAV-based A2G communications [4; 5]. It is vital to extensively conduct channel measurement campaign and develop a wideband A2G channel model to promise an accurate simulation of A2G communication. A comprehensive literature review and analysis of existing A2G channel measurements and modeling of UAV have been provided in [1; 2; 5; 6; 7; 8; 9]. In our previous works, we conducted rotary-wing UAV-based A2G channel measurements at 2.4 GHz, 5.9 GHz, and ultra-wideband frequency band [10; 11; 12]. In [13], the fading characteristics of A2G, channel in different frequency bands are considered and analyzed, based on which a novel autocorrelation model of shadowing is proposed. [PERSON] et al. [14] focus on the fuselage shadowing characteristics of an A2G channel through measurements, and found that placing multiple antennas on a UAV can mitigate shadowing. The authors of [15] analyze the propagation characteristics at different flight attitudes for both line-of-sight (LoS) and obstructed-LoS (OLoS) conditions and propose a new path loss model. As for the studies of wideband channel, the authors of [16] evaluate the Rice factor and root mean square delay spread (RMS-DS) of A2G channel with a bandwidth of 500 MHz. There are other studies on A2G propagation channels based on a wideband channel measurement campaign, as reported in [17; 18]. The authors of [19] propose a geometry-based stochastic channel model in an airport environment. In [20; 21; 22], a tapped delay line (TDL) model is presented for hilly, suburban, and over-water scenarios, where parameters like the probability of occurrence, relative power, phase, duration of individual multi-path component (MPC) are considered. The authors of [23] evaluate the propagation characteristics, in which model planes is fixed in order to simulate inter UAV communication scenario. In this work, a TDL channel model is proposed considering the real motion trajectories of the UAV. As described in previous paragraphs, extensive research has been conducted on low altitudes (below 120 m).