Principle and Performance Analysis of Truncation Pulse Compression in the Decrease of the Radar Blind Zone
In order to improve the range resolution and detection distance of the radar, the method called pulse compression (PC) is commonly used, which not only ensures enough signal energy for the remote detection, but also makes the time-bandwidth products much greater than 1. But if time-width of the pulse signal is increased, as a result the blind zone is also increased inevitably. To solve the issue, we proposed a method named truncation pulse compression, and its principle and performance are analyzed in the paper. This novel method is different from those traditional methods is that it transmits short pulse to reduce blind zone and then combine modulated pulses. It can not only decrease the blind zone, but also can reduce the complexity of radar system. We have performed some simulation experiments to verify the principle of this method, and the simulation results showed that the truncated compressed pulse can effectively solve the problem of the increase of blind zone caused by the pulse compression and reduce the radar system complexity. Introduction As an important modern radar technology, pulse compression technology [1-2]can effectively solve the contradictions of detection range and range resolution of the traditional radar system, which is widely employed in ultra-wideband (UWB) radar[3] and Doppler weather radar [4-6]. Linear frequency modulation (LFM) signal [7] is widely used for pulse compression signal [8-13], and it has the characteristics of large time width and large bandwidth that can assure enough energy for radar system to detect the remote target with high range resolution. However, detection blind zone will be enlarged when the pulse width of the pulse compression signal is increased [14]. It is well known that the detection blind range of the single base station radar system is proportional to the time-duration of the transmitted radar signal, and transmitting additional short pulse is commonly employed to decrease detection blind zone [14]. Recently, some researchers [15] proposed a method which combined one short modulated pulse and one long modulated pulse to solve this problem. Although this method can ensure large detection range and high range resolution, this method has its problem. The first problem is how to choose the time width and time interval of the two pulses, and the second problem is the mutual interference of the two pulses. The final problem, also the most serious one, is that the combined pulse needs radar system to generate and transmit different modulated pulses, and the radar receiver must receives the echo of the short pulse and the long pulse respectively, which can greatly increase the complexity of the single base station radar system. To solve the above problem, a truncation pulse compression method is presented in this paper. The truncation pulse compression can greatly finish the function of combined pulse. And the application analysis of this method using in the radar detection has been made in this paper. The second section described the model of the combined pulses and elaborated the method that how the 207 combined pulses decreased the blind zone. Section III introduced the fundamental principle of the truncation pulse compression and the conditions of decreasing the blind zone, and elaborated the realization of the proposed method in the single radar base station system. Section IV was the simulation of the above principle, and the simulation results showed the feasibility of the truncation compression pulses decreasing the radar detection blind zone. Section V was the results and conclusion of the paper. Combined Pulse Model For the general pulse with a time-duration of T, the time-bandwidth product BT approximates the number of 1, which will be much greater than 1 after processed by pulse compression technique. In this case, the compression ratio D can be expressed as EQ (1): TB B T T D = = = 1 τ (1) Where T is the width of input pulse signal of matched filter, andτ is the width of output pulse signal of matched filter. T is the modulated bandwidth. The compression ratio D is one of the main factors of the pulse compression processing. The combined pulse was to combine two pulses with different time-duration modulated in different compression ratio, was proposed to decease the radar detection blind zone. Moreover, it can ensure those pulses with the same bandwidth which ensure the short pulses remained the same high range resolution with the long pulses. The waveform of combined bi-phase coded pulse is shown in Fig.1. Figure 1. Combined bi-phase coded pulse waveform. Assuming that the pulse width of short pulse was 1 T and the pulse width of long pulse was 2 T , and their modulation bandwidths were B . Then, the compression ratios can be represented respectively as the following equations: