《correcting for distorted antenna patterns in CODAR ocean surface measurements》.pdf

Correcting for Distorted Antenna Patterns in CODAR Ocean Surface Measurements DONALD E. BARRICK, MEMBER, IEEE, AND BELINDA J. LIPA (Invited Communication) Abstract-CODAR systems employcompact antenna elementssuch as cross spectra at each of the antenna elements [l], [2]. From electrically small loops and monopoles toextract bearing information in these solutions, estimates of radial current velocity versus oceansurfaceobservations.Pastanalysismethods haveassumedthat range andbearing are constructed. Assumed inthe use of these theseelementpatternsare perfect,i.e.,cosine and omnidirectional. closed-form solutions are: a) perfect omnidirectional patterns Operations from metallic offshore platforms usuallydistortthesepat- ternsbecause of unavoidableobjects intheirnear field. Whensuch for each of the monopole antenna elements, and b) no noise distortions areignored,previous methods are shown to produce -35 added to the receivedsea-echo signal voltages. In [5] it is rms bearingerrors.Thereforeleast-squares methods arepresentedand shownthatmutual interaction among the four elements, demonstrated that deal with differential element pattern distortions. It is neglected in the closed-form solutions, Will produce sufficient shown how the required relative patterns are easily measured by a boat circling the antenna, and these patterns are then stored as look-up tables pattern distortion to cause bearing biaseswith this system. in theleast-squaresinversion methods. Relativepatterns (i.e., one Although mutual interaction among elements is not a problem element pattern divided by the other), rather than