CODAR Directional Biases with a Four-Element Antenna Array

Directional biases are shown to exist for a four-element square CODAR receiving array used for coastal current mapping. The sources being sidelobes and mutual coupling (a type of pattern distortion), these nonstatistical biases depend both on the geometry/size of the square array as well as the particular closed-form algorithm employed to estimate bearing. Typical rms errors due to these sources lie between 5-15°. Reconfiguration of the four-element antenna geometry may reduce sidelobe biases when closed-form algorithms are employed, but only at the expense of increased mutual-coupling bias. A least-squares algorithm is given that corrects for pattern distortion, circumventing this shortcoming of closed-form methods; this algorithm can also improve sidelobe biases. Other antenna systems possessing no sidelobes are in use for CODAR that eliminate these sources of error.