The development of an effective jam code against the conical-scan seeker

Abstract

There remains a wide proliferation of second-generation frequency-modulated conical-scan seekers in the hands of irregular forces, while the understanding of what makes a jam signal effective remains unclear. It is generally known that the jam-to-signal (J/S) ratio, the jam signal frequency, and the duty cycle are the parameters that need consideration when developing an effective jam code, but the effect of using different jammer waveforms is not generally known. The general consensus in the literature seems to indicate that the effective jam signal parameters should be close to those of the target signal. It is known that the jam signal that matches the target signal will only beacon the target and not provide protection, therefore the jam signal should not perfectly match the target signal for effective jamming. However it is not clear which parameters should be close to and which should differ with the target signal. The literature also generally uses the low frequency type of jam signal and the effect of other types of waveforms is not known. Due to the sensitive nature of this topic, a simulation model and a hardware model of the conical scan seeker was not available to the author and as a result a representative simulation model was designed for conducting the experiments. The simulation model was extensively tested and validated to ensure representative behaviour. This study investigated the effect of the critical jam signal parameters against different jammer waveforms namely: the fixed carrier, low frequency, amplitude modulation (AM), frequency-modulation (FM) and the AM-FM jam codes. The study tested the effect of the critical parameters across the different jam waveforms and a comparison of the tested waveforms was conducted. The parameters used to compare the jam signals were the maximum achieved seeker error, the minimum J/S ratio required to achieve a significant effect, the range of effective frequencies or modulation indices and the lowest effective duty cycle. The AM jam signal achieved the greatest seeker error when compared to the other jam waveforms with a maximum error of 1.1°. The AM jam signal however achieves this error, with a J/S ratio of 50. The AM-FM jam signal achieved an error of 0.97° at a J/S ratio of 20 which is less than half of the required J/S ratio with the AM jam signal. The AM-FM hybrid jam signal was found to be the most robust in a wide range of modulation indices. This jam waveform was found to be the least sensitive against changes in the modulation index. The jam signal was found to be less power intensive when compared with other waveforms since significant jam effect was achieved at low J/S ratios. The best parameter combination for this jam signal was a J/S ratio of 20, a modulation index of 2.5, a modulation frequency of 100 Hz and a duty cycle of 50%. The maximum seeker error induced by this parameter combination is 0.97°. With the stated advantages, the AM-FM hybrid jam signal was found to be the most effective jam signal against the conical-scan seeker. Contrary to the general guide provided in the literature, the most effective jam signal does not contain parameters that are similar to the target induced parameters. The conclusion of this work was therefore that the most effective jam signal does not necessarily have to be similar to the target signal to be effective against the conical-scan seeker. The unique result found in this study is attributed to the wide range of jam signal waveforms that were tested. The results show that the effects of the critical parameters (J/S ratio, frequency and duty cycle) vary with the change in jam waveform.