maximum likelihood estimation
The article addresses the issue of measuring the azimuth at different options for constructing an antenna system at surveillance airborne radars.
Surveillance is performed by mechanical rotation of the antenna, while the following options are considered:
- The formation of two partial reception beams, symmetrically spaced in azimuth relative to the transmitting beam;
- Formation of a single receiver beam coinsiding with transmitting one.
The radar works in MTI mode with a narrow-band Doppler filtering based on DFT. The expressions for the likelihood ratio of the sample signals received at successive intervals of coherent processing (frames) are defined.
Using the expressions for the likelihood ratio, equations defining maximum likelihood azimuth estimates were obtain. It is shown that with the joint information processing of the partial beams optimal estimate is the estimate of the maximum azimuthal batch. It does not require the use of monopulse measurement method.
Given that the likelihood ratio is formed only at discrete points (on successive frames), different interpolation algorithms are used to determine the position of its maximum. The variants of discriminators for direct search of the maximum, as well as algorithms based on interpolation of zero derivatives are considered.
Effectiveness of different algorithms is estimated by statistical modeling. A comparative analysis is performed, and the results proved that some maximum likelihood estimates are quite useless. The advantage of the suboptimal algorithms under real operating conditions of surveilliance radar (SNR is less then 20dB) is demonstrated. It is demonstrated as well, that all algorithms considered and recommended have approximately the same characteristics, and the question of choosing any of them is determined by the scheme for constructing an antenna system.