Analysis of performance of multiple beam digital beamforming antenna arrays by simulation

Conventional antennas of high directivity lack versatility and are inefficient for scanning or for detecting transient sources. Digital beamforming (DBF) is a technique which has the potential to overcome these limitations, because it allows formation of many simultaneous beams from a single array. If the number of beams is large enough, DBF can be used to form a radio image. DBF imaging offers advantages over conventional interferometric radio imaging for some applications. The principal disadvantage of DBF is that very high computation rates are required for most applications. This dissertation investigates several aspects of the practical implementation of DBF systems. The principal research technique is simulation, using a model system developed for this work and described here.; Because of limitations in the performance of analog/digital converters, many applications of digital beamforming will require conversion of the received signals to an intermediate frequency before sampling. This work shows that time-delay beamforming performed at intermediate frequencies severely limits directional performance, and describes method for modifying the beamforming to compensate. Simulations demonstrating the failure of the operation with unmodified filters and successful beamforming with appropriate modified filters are presented.; It is also shown that almost every aspect of the design of a DBF system is influenced by the quantization of the received data and it is important to choose the minimum number of quantizer levels necessary to achieve the necessary performance. Simulations described here demonstrate that the directional performance of DBF arrays is not strongly affected by quantization. However, the simulations also show that quantization and interpolation noise are not independent across the elements of an array and quantization noise may not decrease as the array size increases.; Because a major constraint on the implementation of digital beamforming systems is the large amount of computation required, this work has also investigated the applicability of the fast Fourier transform (FFT) as a beamforming technique. It is shown that the FFT offers computational advantages under certain limited conditions, which are identified. However, there are many applications for which the FFT is unsuitable as a beamforming technique.