AOA measurement error under the antenna couplings

This paper reports the angle of arrival (AOA) measurement error due to the coupling of an antenna which is used for the frequency close to that under the measurement. The coupling of sensors which is ignored in most cases of acoustic problems is one of the essential effects for electromagnetic measurements. An example of this phenomena is observed with the AOA subsystem of an airborne collision avoidance system (ACAS). Some onboard antennas are the error sources as the coupled scatterer to the AOA antenna. In this paper, the effect of the coupled scatterer on the airborne AOA antenna is discussed. The received signals of the antenna elements are calculated by solving the coupled antenna problem directly. The AOA error by the scatterer is estimated from these signals by assuming an AOA estimator. The AOA error is measured by anechoic chamber experiments. The relation between the AOA measurement error and the scatterer location is discussed. The signal processing method which can reduce the AOA error under the antenna coupling is needed for the improvements of ACAS.