## 1 Introduction  
Passive sensing systems generally use the electromagnetic waves of external radiation source, such as FM broadcast, satellite, digital TV broadcast, etc. It has many advantages, such as anti-stealth, strong survivability, low cost, and not affected by active directional interference; however, the power of the receiver is insufficient for effective target sensing in many cases [1, 2]. Among many external radiation sources for passive sensing, satellite communication waveforms have high coverage and availability. Thus, target sensing based on satellite communication waveforms has great potential [3, 4]. Forward scatter radar is a bistatic radar configuration with a special geometry, in which the target is located between the transmitter and the receiver. This means that the bistatic angle is close to 180\({}^{\circ}\)[5]. Compared with conventional radar systems, its main characteristics is scattering. In addition, the radar cross section (RCS) of the target is high in the case of forward scatter [6]. If the moving target crosses the baseline, it is easier to sense target. This allows the forward scatter radar to use satellites as sources of illumination to sense the target. Meanwhile, although the forward scatter area is very narrow, the richness of the satellite and the convenient handling of the receiver make the satellite forward scatter radar capable of sensing aerial target in a wide area. Many works have been conducted on forward scatter radar (FSR) [7, 8, 9, 10]. In particular, there has been progress on the sensing of ground, sea, and aerial targets by the forward scatter radar. For ground target sensing, [PERSON] et al. constructed a forward scatter system based on the power spectrum difference generated when crossing the baseline [11]. For marine target sensing, transmitters and receivers were set up on both sides of the strait to sense ships that cross the baseline, and echoes with large differences were observed [12]. Reference [13; 14; 15; 16] used machine learning to detect and classify targets, which improved the efficiency of target detection of synthetic aperture radar (SAR). Since the satellite has a low receiving power, and the FSR system has a large radar cross-sectional area, the use of satellites as external radiation sources to construct FSR systems for the aerial target sensing is also one of the important areas of FSR systems. In [17], the characteristics of the forward-scattered GPS signals were studied when the aircraft crossed the vertical baseline. Numerical results demonstrated that the height of the target crossing the highest point, the azimuth, speed, and other factors from the receiver had considerable impact on the amplitude of the received signals. The use of satellites as forward scatter radars for passive sensing of aerial targets was studied in [18; 19]. In [20], the method for extracting the current signal based on the traditional satellite tracking loop was studied and verified by many field experiments. During the target movement, the FSR signal produces an appropriate Doppler frequency shift [21]. This work provided a simplified model of the received signal and analyzed its Doppler characteristics in [22]; however, none of these works has focused on extracting the characteristics from satellite communication waveforms for target sensing; therefore, it is of great significance to study the problem of aerial target sensing in the case of forward scatter. In this paper, a novel satellite communication waveforms-based aerial target sensing method is proposed, and the main contributions of this paper are as follows:  
* In order to purify the signal, a zero-notch filter is used to separate the direct wave signal.