## 1 Introduction  
With the development of synthetic aperture radar (SAR) technology, the SAR carrier has been developed from the initial airborne and spaceborne platforms to the unmanned aerial vehicle, missile and vehicle-mounted platforms [1, 2]. The near space, as a new space outside the traditional active area of vehicles, has attracted wide attention for its unique advantages in recent years, and the relevant exploring research has become a new topic in SAR imaging [3, 4]. Compared with the conventional airborne platform, the hypersonic platform mainly works in the typical altitude of 20-100 km, which helps to achieve a wider range of observation. Meanwhile, the integrated design of this platform is considered to improve the stealth performance, and the cruising speed is usually more than 5 Mach to achieve the fast response. Therefore, the detection, tracking and interception probability on this platform would be relatively low for the hostile defense system [5, 6]. In addition, the flight trajectory of this platform is not constrained by the special orbitscompared with the spaceborne platform. Thus, the flexible maneuvering characteristics are beneficial to reducing the revisit time on the coverage of the focused area [7]. The spatial geometric variation between the radar platform and the targets located in the imaging scene determines the Doppler history of SAR echo signals. Therefore, it is a key point to construct an appropriate signal model relying on the motion trajectory and the imaging mode of the SAR platform. For airborne SAR, when the turning slope angle and the flight path angle of the vehicle are constants, the turning radius is determined by its instantaneous velocity [8]. In general, the SAR imaging geometry model of the conventional airborne platform is established based on the linear flight trajectory. In contrast, to avoid the tracking and interception of the hostile defense system, the flight path of the hypersonic platform undertaking the reconnaissance task is planned as a curved trajectory. Moreover, the turning radius of this platform could be hundreds of kilometers because of its high instantaneous velocity. Thus, the motion trajectory is characterized as an approximate arc shape, which forms an arc band-shaped coverage. Affected by the curved trajectory of this platform, the range migration becomes more obvious. At this point, when the SAR imaging is processed with the traditional hyperbolic range model, the imaging quality of targets would be seriously degraded, or even cannot satisfy the performance requirements of the SAR system. For this problem, an accurate range model matched with the curved trajectory of the hypersonic platform is presented in this paper. In addition, under the constraint of minimum antenna area [9], the contradiction between the high resolution and wide swath (HRWS) becomes more serious for the hypersonic platform SAR. With a large increase of this platform velocity, a higher Doppler bandwidth is required to achieve the specific azimuth resolution. Accordingly, the pulse repletion frequency (PRF) should be higher to avoid azimuth ambiguity. However, the high PRF will limit the swath range; otherwise, it will make range ambiguity worse. Therefore, for the conventional single channel SAR system, the PRF selection is compromised between HRWS requirements [10]. To alleviate this contradiction, [PERSON] [11] proposed the multichannel receiving displaced phase center antenna (DPCA) technique, based on which the Doppler ambiguity resulted from a low PRF can be separated by increasing the spatial sampling degrees of freedom. On this basis, [PERSON] [12] discussed the advantages of applying the azimuth multichannel transceiver technology in detail, and [PERSON] et al. [13; 14; 15] verified the effectiveness of HRWS applications with the simulation results of the traditional spaceborne and airborne platform.