Millimeter-wave and terahertz imaging techniques

Abstract

This thesis presents the development and assessment of imaging techniques in the millimeterwave (mmW) and terahertz frequency bands. In the first part of the thesis, the development of a 94 GHz passive screener based on a total-power radiometer (TPR) with mechanical beamscanning is presented. Several images have been acquired with the TPR screener demonstrator, either in indoor and outdoor environments, serving as a testbed to acquire the know-how required to perform the research presented in the following parts of the thesis. In the second part of the thesis, a theoretical research on the performance of near-field passive screeners is described. This part stands out the tradeoff between spatial and radiometric resolutions taking into account the image distortion produced by placing the scenario in the near-field range of the radiometer array. In addition, the impact of the decorrelation effect in the image has been also studied simulating the reconstruction technique of a synthetic aperture radiometer. Guidelines to choose the proper radiometer depending on the application, the scenario, the acquisition speed and the tolerated image distortion are given in this part. In the third part of the thesis, the development of a correlation technique with optical processing applicable to millimeter-wave interferometric radiometers is described. The technique is capable of correlating wide-bandwidth signals in the optical domain with no loss of radiometric sensitivity. The theoretical development of the method as well as measurements validating the suitability to correlate radiometric signals are presented in this part. In the final part of the thesis, the frequency band of the imaging problem is increased to frequencies beyond 100 GHz, covering the THz band. In this case the research is centered in tomographic techniques that include spectral information of the samples in the reconstructed images. The tomographic algorithm can provide detection and identification of chemical compounds that present a certain spectral footprint in the THz frequency band.