Design Of Near-field Wideband Frequency Invariant Circular Arrays

Array signal processing is that specialized branch of signal processing that focuses onsignals conveyed by propagating waves. An array i.e. a group of sensors located at distinctspatial locations is deployed to measure a propagating field. The array samples the field at thesensor locations and time instants. The sensors serve as transducers converting field energy toelectrical energy. The array collects these waveforms to create the output signal. Array signalprocessing finds numerous applications in the areas of medical diagnosis and treatment, radar,sonar, communication, acoustics and seismology. Beam forming is a technique of array signalprocessing employed to form beams in order to receive signals impinging from particulardirections while attenuating signals from the other directions. In majority of the signalprocessing literature the source is assumed to be in the far field of the array or at an infinitedistance from the array. The resulting received waveform appears to come from a single pointsource with a planar wave front. This methodology simplifies the solution of the beamforming design problem. However, in many applications the source exists within the nearfield of the array and the signal has a spherical wave front thus assumption of far field resultsin severe degradation of the beam forming pattern. In medical imaging applications like MRIthe signal is usually in the near field of the array.Wideband beam forming has recently attracted the attention of research community. Thesignal of operation in beam forming applications in generally a wideband signal that meansthat it occupies a certain bandwidth and the methodology used to process narrowband signalsdoesn‘t work on the wideband signals. Different architecture has to be employed to processthe wideband signals in order to get a feasible output.The work in this thesis is related with the signal processing of wideband signals presentin the near field of the circular array to achieve unity gain for the target/focal point, predefined side lobe attenuation for the stop band points and a constant beam width pattern forthe frequency range of interest in the wideband signal. The design problem will be solvedusing different techniques available in the literature. The design work has been divided intotwo parts. The first part deals with the design problem formulation in the frequency domain while the second part shows the work in the time domain. The results show the effectivenessof the proposed mechanism.