## 1 Introduction
The single-link MIMO system was originally developed on the basis of virtual array elements. Different methods to realize the physical structure of the single radio frequency (RF) link radar receivers are discussed in [20]. The single RF link MIMO transmission system was investigated more systematically in [21]. The antenna feed terminal entity element in the MIMO system was replaced by a virtual antenna element, and the transmitter array was more efficient by using the binary phase shift keying (BPSK) modulation. This technique not only solves the size problem of MIMO antennas, but reduces the mutual coupling between antennas, which greatly improves the efficiency of MIMO systems. The single RF link MIMO-OFDM system was proposed [22; 23; 24] to realize the purpose of multicarrier signal transmission. Several signals were superimposed in the time domain and the OFDM waveform was finally formed. This solves the problem of replication interference caused by the beam switching in the receiver of MIMO antennas compared to the previous systems. A beam-switched antenna was realized by using eight parasitic antenna elements and PIN diodes, which effectively met the demand of generating more waveforms at the transmitter. A compact frequency tunable single RF link MIMO transmission scheme was proposed in [25]. This approach simplifies the DC bias circuit and various loads in the BPSK modulation, so the external reconfigurable matching circuits can be omitted for simplification. A virtual array is created by sending independent waveforms from the transmitting array to the receiving array, which improves the degrees of freedom of phased array and MIMO systems. This kind of MIMO radar reduces false alarms and increases its robustness to noise [26]. Traditional algorithms are usually applied in the ideal sparse environment, however, MIMO radar signals are not sparse enough in the time and frequency domains. Therefore, the time frequency ridge estimation algorithm was proposed [27] to improve the reconstruction accuracy of MIMO radar signals. To suppress the high grating lobes in the near-field imaging results in MIMO synthetic aperture radar array, the relationship between the target's point spread function and the transmitter/receiver (T/R) array pattern was studied, and the proper height of the T/R arrays was adjusted to focus on the near-field edge points perfectly [28; 29; 30; 31]. A colocated algorithm was presented for distributed MIMO radar systems in [32]. In order to estimate the location parameter, range sum measurements were performed to determine the distance between the receiver and the target. As for the single RF link MIMO radar, it can achieve a similar performance for the same target distance with a small detection error rate. Besides, considering the simplicity and cost-effective advantages, it is a good candidate for wireless communications. In this work, using the switch parasitic antenna as the carrier, the single RF link MIMO radar was studied to realize the traditional MIMO measurement ability of velocity and range. Based on the single RF link technology, the MIMO radar antenna was optimized to achieve better system performance. A simulation platform was established to verify the method and the correctness of single RF link MIMO theory. Several important modules of the single RF link MIMO radar system will be introduced, and the differences between the single RF link MIMO radar system and the conventional MIMO radar system will be discussed in detail. The remainder of the paper is organized as follows. Section 2 describes the working principles of MIMO radar, combining the single RF link chain with the MIMO system. Section 3 introduces the establishment of single RF link MIMO radar simulation platform and gives the implementation method for each part of the MIMO system. The main factors that influence the single RF link MIMO radar performance are discussed in Section 4. A method based on the simulation results is put forward to increase the system robustness. Finally, the conclusion is given in Section 5.