methods perform dynamic focusing of a coherent array imaging system are invented . dynamic focusing in ultrasonic array imaging involves extensive real - time computations and data communication . particularly for real - time three - dimensional imaging using fully - sampled two - dimensional arrays , implementation of dynamic focusing can be extremely complicated . the invention described in this disclosure greatly simplifies the delay control mechanism by exploiting both spatial and temporal characteristics of the focusing delay patterns . the simplification primarily results from grouping adjacent channels into sub - apertures for the range dependent focusing component , and non - uniform quantization of the delay values .