## 1 Introduction  
In active radar system, the target identification ability is closely associated with average transmission power. Limited by the finite peak power, the promotion of target identification ability usually depends on the increase of transmission pulses' bandwidth. However, the increase of transmission pulses' bandwidth will degrade the range resolution. To resolve the contradictions between the identification ability and the range resolution, a process of broadening the pulses' bandwidth in transmitter and compressing them in receiver is utilized. This technique is called pulse compression [1] and its schematic diagram is shown in Figure 1. The input measured signal is mixed with the chirp modulation signal to expand its bandwidth, then the modulated signal is compressed into pulses by a digital pulse compression method or an analog dispersive device. An analog dispersive device of surface acoustic wave (SAW) filter was previously used for pulse compression; nowadays, methods of digital pulse compression are frequently utilized for signal expansion and pulse compression instead of SAW filters [2; 3]. As early as in 1960s, the technology of radar pulse compression was firstly utilized to represent Fourier transform by [PERSON] [4]. Afterwards, a much more detailed discussion of spectral analysis utilizing the radar pulse compression was described by [PERSON] [5]. Nowadays, the [PERSON]' system is known as the chirp transform spectrometer (CTS). In a CTS system, the pulse compression is usually realized by using the SAW filters and this makes it possible to apply to real-time spectrum measurement. The CTS system was later spread to the field of atmospheric radiation measurement by [PERSON] and [PERSON] [6], [PERSON] et al. [7; 8; 9], and [PERSON] [10]. An improved CTS system with a novel digital dispersive matching network instead of the SAW devices for signal expansion helped to improve the accuracy of the measured spectrum and the system's linear response, which greatly improved the system's performance [11]. As a new passive detection method, the CTS back-end was developed into a mature tool widely used in weather and astronomical observation. Early in the 1990s, CTS back-end had been applied for ground-based submillimeter observation of planets [12] and comets [13]. Subsequently, CTS was used for atmosphere components investigation of Comet Chyruymov Gerasimenko in Rosetta Orbiter, which was launched in 2004 for deep-space detection [14]. With the advantage of high spectral resolution and high stability, the CTS back-end was mounted on the high-resolution spectrometer of the German Receiver for Astronomy at Terahertz Frequencies (GREAT) on board the Stratospheric Observatory for Infrared Astronomy (SOFIA) for planetary and cometary research in recent years [15; 16; 17; 18; 19]. Compared to fast Fourier transform (FFT) algorithm, the CTS has relatively low weight and power consumption, high spectral resolution and extremely high stability, which makes it quite suitable for space/airborne applications to make a study of comets, planetary atmospheres, interstellar medium, and even early universe. In the classical CTS system, a push-pull arrangement with two uniform channels are adopted to make up the bandwidth mismatch between the expander and compressor. This two-channel arrangement helps to guarantee the maximum sensitivity that can be obtained for the instrument. However, the frequency accuracy and amplitude consistence are directly affected by the match between the two channels. This matching problem, especially the match between different SAW filters, may increase the difficulty of hardware implementation. Meanwhile, the doubled devices also increase the mass and power consumption of the CTS system. In this paper, a new conception of single-channel CTS system with less components was developed.