SPECIAL REPORT: ELECTRONIC COUNTERMEASURES
A reactive jammer has a lot of advantages over barrage jammer; for example, a barrage jammer must transmit constantly and so will drain its batteries quickly.
to produce multiple candidate solutions for the receive antenna height. In general, some solutions will be higher than the transmit antenna, and some lower, so they can be placed into groups: a high height hypothesis group, and a low height hypothesis group. If the receive antenna height is known to be lower than the transmit antenna, the higher height solutions can be rejected as inadmissible. If that information is not available, or not immediately available, the best approach is to carry both sets of hypotheses forward until such time as one set can be rejected. This is an important example, because ECM antenna height is a strong determining factor in ECM protection range. The disambiguation problem is rich in other ways too, especially for a multidimensional problem. For example, suppose the genetic algorithms have produced a pool of candidate solutions from which we need to extract the best candidate. We know something about how propagation works phenomenologically, so if we accept a particular solution for the range between the receiver and transmitter, that tells us something about the necessary relationship between frequency and antenna heights. If the
range is correct, a small wiggle in frequency should cause received power to wiggle by xyz dB. If the range solution is incorrect, then the same frequency wiggle will produce a different wiggle in received power. The design of a device to provide this kind of ability is an interesting one, not just for counter-IED applications, but for other remote sensing applications as well, perhaps in the telecommunications industry. It’s easy to imagine an intelligent device which continuously conducts its own scientific experiments on the environment based on meta-analysis of real-world measured power measurements, using transmitter frequency, power and phase as its tools. A detailed discussion of disambiguation techniques is out of scope for this paper, as is the performance enhancement that accrues from using a combination of disambiguation techniques, though they may be treated in future papers. There’s a final important point I want to make in this section concerning disambiguation by frequency diversity, and in a minute I’m going to relate it to reactive jammers: all pilot signals are not created equal. Some frequency choices
FIG. 6: EXAMPLE OF SOLUTION AMBIGUITY WHEN USING THREE PILOT SIGNALS
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