Omnidirectional beam forming for linear antennas by means of interpolated signals

With Shannon sampling rates at the sensors of a linear antenna, it is not always possible to achieve a beam system with complete azimuth coverage. Furthermore, it is not possible to compensate an antenna system platform\´s own motion in such a way as to be able to build up a beam system fixed in space. Even the method of increasing the sampling rate for the sensors to an impracticably high value would only solve these problems to a limited extent. On the other hand, a solution which is easily put into practice is offered by time interpolation between adjacent sample points of the sensor signals. Therefore we have investigated this method in detail. The beam patterns are formed by special linear combination of the autocorrelation function (ACF) of the sensor signals. This kind of linear combination is applicable to all types of interpolation between adjacent sample points. For one special type of interpolation, namely linear interpolation, an azimuthal level-distribution function which specifies the maximum antenna reception sensitivity for all steering angles is stated for a linear antenna having sensors. With this function, it is possible to estimate the influence of the sampling frequency, Signal center frequency, signal bandwidth, and antenna dimensions on the antenna/beamformer performance.