The laboratory model of a microphone has been designed for estimating the directional properties of a stationary sound field. In order to obtain high angular resolution, the principle of synthetic aperture, known in radar as well as in sonar, has been utilized. An omnidirectional microphone attached to the end of a holder rotates step by step at a periphery. The signals received by the microphone are digitized, then delayed and summed up. The possible number of beams to form is equal to the number of microphone positions, e.g. 120. This results, at a frequency of about 4.5 kHz, an angular resolution of 3 °.
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