Abstract
We present a method to enhance the accuracy of platform-based, high-frequency (HF) direction-finding (DF) systems using dynamic mode selection. To improve bandwidth and efficiency, the metallic platform supporting the DF array is used as the primary radiator by employing electrically small antennas to excite linearly independent combinations of its characteristic modes (CMs). However, the radiation characteristics of these modes vary dramatically over the HF band, making it difficult to achieve consistently good DF accuracy with a fixed system. To alleviate this, we propose a dynamic mode selection strategy to achieve enhanced DF accuracy. This strategy is based on the assumption that the number of available CMs of the platform is greater than the number of available coherent receive channels. Thus, dynamic mode selection allows for choosing the optimal antenna combination to obtain the best DF accuracy at each frequency. This strategy is demonstrated for an airborne DF system employing five electrically small antennas and up to four coherent receive channels. We demonstrate the efficacy of the proposed approach using computer simulations and scaled-model experiments. Simulation and measurement results show that dynamic mode selection can significantly enhance the DF accuracy of platform-based HF DF systems using a limited number of coherent receive channels.
Highlights
T HE high-frequency (HF) band (3-30 MHz) is widely used in many military and some civilian applications
We presented a method for enhancing the accuracy of platform-based HF direction finding systems that use DF receivers with a limited number of coherent channels
It is feasible to use numerous, electrically small coupling elements to excite linearly independent combinations of the characteristic modes of the platform. Using these electrically small antennas as the elements of a DF array is analogous to using the pure CMs of the platform to perform direction finding
Summary
T HE high-frequency (HF) band (3-30 MHz) is widely used in many military and some civilian applications. We present a method for improving the accuracy of a platform-based HF DF system that uses a receiver with a limited number of coherent receive channels We assume that such a system uses electrically small antennas (ESA) to excite the characteristic modes of the platform and. The performance of the full-scale platformbased DF system is evaluated using computer simulation tools and DF modeling techniques These results show that using a dynamic mode selection algorithm, the DF accuracy of the system can be substantially improved across the entire HF band. In this work, we will only consider the first five CMs of the platform to design the proposed DF system These five modes will provide a sufficiently high number of unique mode combinations (for 2-4 receive channels) to improve the DF accuracy by selecting suitable mode combinations as frequency or field of view is changed. ICEs should be placed at current maxima locations and CCEs should be placed at current minima locations [13]-[15]
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