HIGH RESOLUTION RADAR SYSTEM USING LINEAR FREQUENCY MODULATION PULSE COMPRESSION AND ANTI JAMMING ABILITY

• Main Author: Prastiya Wibawa, Yoga
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/50578
• Institution: Institut Teknologi Bandung

In conventional pulsed radar, there is an interrelated problem between pulse duration and its detection distance. Short pulses produce higher distance resolution but do not generate sufficient pulse energy to detect longer distances. In addition to a more limited detection distance, pulses are also very easily interfered with by noise and jammers. Because the pulse duration is related to the pulse bandwidth, the linear frequency modulation (LFM) pulse compression method can be made pulses with a wider bandwidth without depending on the duration. So it can be made a radar with a high resolution distance with a long pulse duration. By using a radar with LFM pulse compression in addition to producing high range resolution, this method can also increase the resistance of the radar signal to noise and other interference. This is thanks to the high processing gain obtained from the matched filter process. The matched filter process will reduce noise and interference signals that have different characteristics from the reference or replica signal. With high noise resistance, this radar system also meets the requirements of a defense radar that is anti-jamming and capable of operating at a low probability intercept (LPI). So that the opponent has difficulty jamming or detecting radar signals. However, a radar with simple LFM pulse compression will be very easy to jam if the signal can be imitated by the opposing party using digital radio frequency memory (DRFM). So a method is needed so that radar pulses have a waveform that is not easily intercepted with DRFM. This can be done by exploiting technical weaknesses on the DRFM side. In addition, the LFM pulse compression radar also has a Doppler shift problem which can cause the estimated target position generated by the matched filter to shift. The magnitude of the shift in the estimated position is due to the carrier frequency, target speed and pulse duration. So that this becomes a limitation in designing the LFM radar pulse waveform. The higher iv the carrier frequency and the longer the pulse duration, the greater the shift in target estimation. So for that it is also necessary to develop the LFM modulation method to overcome the problem of this shift in position estimation. The pulsetrain method studied increases the complexity of the waveform to prevent signal interception and jamming with the copy and retransmit technique. Thus increasing the resistance of the radar system to jamming signals with a simple LFM which has the same duration and bandwidth characteristics as the radar signal. This method can also overcome the shift in the target estimation on the radar. A simple pulsetrain consists of 2 subpulses with coherent modulation. In the case of close range targets, a pulsetrain LFM pulse with 2 coherent subpulses with a total duration of 80 µs was used. The use of a short duration apart from minimizing the blind zone distance can also correct the shift in the estimation of the target. Whereas for long-range target classification used pulsed LFM pulses with 2, 4 and 8 coherent subpulses with a total duration of 400 µs. The use of pulsetrain with 4 and subpulses resulted in a correction of the shift in the estimated position of the target by 44.54% and 58.01% of the shift in the estimated position with 2 subpulse, respectively. For the 200 MHz LFM pulse bandwidth in this study, the simulation resulted in a value (1.527 ± 0.056) m and a compression factor of 39.03 dB and 46.02 dB for pulse duration of 80 µs and 400 µs respectively.