Millimeter-wave and terahertz imaging techniques

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.Postprint (published version

TERASENSE: THz device technology laboratory

The use of THz frequencies, particularly W and G band allows reaching higher resolution and deeper penetration in emerging applications like imaging, sensing, etc. The development of those new applications lays on reliable technologies, background of expertise and know-how. The CDS2008-00068 TERASENSE CONSOLIDER project has given the opportunity to extent upwards in frequency the previous background of the microwaves research group partners. This article summarizes the developments of the TERASENSE work package “THz Device Technology Laboratory”

TERASENSE: THz device technology laboratory: final summary

The use of THz frequencies, particularly W and G band allows reaching higher resolution and deeper penetration in emerging applications like imaging, sensing, etc. The development of those new applications lays on reliable technologies, background of expertise and know-how. The CDS2008-00068 TERASENSE CONSOLIDER project has given the opportunity to extent upwards in frequency the previous background of the microwaves research group partners. This article summarizes the developments of the TERASENSE work package “THz Device Technology Laboratory”.This work was supported by the Spanish Ministerio de Ciencia e Innovación through the CONSOLIDER-INGENIO 2010 program reference CSD2008-00068 TERASENSE

Research development of terahertz imaging systems

The electromagnetic radiation at a terahertz frequencies (from 0.1 THz to 10 THz) is situated in the frequency band comprised between the optical band and the radio band. The interest of the scientific community in this frequency band has grown up due to its large capabilities to develop innovative imaging systems. The terahertz waves are able to generate extremely short pulses that achieve good spatial resolution, good penetration capabilities and allow to identify microscopic structures using spectral analysis. The work carried out during the period of the grant has been based on the developement of system working at the aforementioned frequency band. The main system is based on a total power radiometer working at 0.1 THz to perform security imaging. Moreover, the development of this system has been useful to gain knowledge in the behavior of the component systems at this frequency band. Moreover, a vectorial network analyzer has been used to characterize materials and perform active raster imaging. A materials measurement system has been designed and used to measure material properties as permittivity, losses and water concentration. Finally, the design of a terahertz time-domain spectrometer (THz-TDS) system has been started. This system will allow to perform tomographic measurement with very high penetration resolutions while allowing the spectral characterization of the sample material. The application range of this kind of system is very wide: from the identification of cancerous tissues of a skin to the characterization of the thickness of a painted surface of a car

Design of a dual-band circularly polarized antenna for a Galileo demonstrator

This Master Thesis presents the design of a novel antenna geometry for Galileo satellite navigation systems. This radiator is intended to improve the performance of an already designed antenna for the GALANT DLR’s internal project. Finally a dual-band, right hand circularly polarized, with isolated outputs, stacked patch microstrip antenna has been designed to fulfil the objectives of the project. The most important characteristic of this antenna is that it can be fed separately for the low frequency band and for the high frequency band with an isolation better than -25 dB between ports. This is the reason why the Institute of Navigation decided to register the patent of this antenna. The name of the invention is: “Dual-Band Circularly Polarized Microstrip Antenna with Two Isolated Outputs Suitable for Navigation Systems”. The work has been structured in the following manner: First, a complete research on microstrip antennas is carried out, reflecting in this report only the ones that fit better to our specifications. Afterwards, an antenna geometry is chosen and approximately one month and a half is spent in order to adjust the characteristics in RF simulation applications. Once good results are obtained in the simulations, the chief of the department decides to register the patent of the antenna. Finally, the antenna is constructed and measured to check the results of the simulations. Moreover, at the end of the work period, a first adaptation of the antenna in order to build an array is carried out. Basically the adaptation consists on inserting the 90° Hybrids in the feeding layer of the antenna while taking into account restrictions in size

Design of a dual-band circularly polarized antenna for a Galileo Demonstrator

Projecte fet en col.laboració amb l'empresa DLRThis Master Thesis presents the design of a novel antenna geometry for Galileo satellite navigation systems. This radiator is intended to improve the performance of an already designed antenna for the GALANT DLR’s internal project. Finally a dual-band, right hand circularly polarized, with isolated outputs, stacked patch microstrip antenna has been designed to fulfil the objectives of the project. The most important characteristic of this antenna is that it can be fed separately for the low frequency band and for the high frequency band with an isolation better than -25 dB between ports. This is the reason why the Institute of Navigation decided to register the patent of this antenna. The name of the invention is: “Dual-Band Circularly Polarized Microstrip Antenna with Two Isolated Outputs Suitable for Navigation Systems”. The work has been structured in the following manner: First, a complete research on microstrip antennas is carried out, reflecting in this report only the ones that fit better to our specifications. Afterwards, an antenna geometry is chosen and approximately one month and a half is spent in order to adjust the characteristics in RF simulation applications. Once good results are obtained in the simulations, the chief of the department decides to register the patent of the antenna. Finally, the antenna is constructed and measured to check the results of the simulations. Moreover, at the end of the work period, a first adaptation of the antenna in order to build an array is carried out. Basically the adaptation consists on inserting the 90° Hybrids in the feeding layer of the antenna while taking into account restrictions in size

Dual-band circularly polarized microstrip antenna with two isolated outputs suitable for navigation systems

This paper presents the results of the development of a microstrip antenna that presents dual-band operation. Each band is coupled to separated ports, so that no additional diplexer is needed. Simulated results showed that a high isolation between this two ports has been obtained

Dual-band microstrip antenna for a robust navigation receiver

The design of robust navigation systems requires the receiver to be nearly immune against interference coming from several different sources, such as hand-sets and base stations for mobile communications, and military radars. One way to minimize the effects introduced by such interferers is to place pass-band filters with low insertion loss between the antenna and the low-noise amplifier (LNA). In order to increase robustness, the antenna itself can be designed to operate only in the desired bands, so that only low power levels in the out-of-band region are received. In order to receive the signals in the E5a-E5b and L1 bands of the European Galileo system, a dual-band antenna may be used. Several topologies presenting multi-band characteristics have been already proposed in the literature. In some of the cases, the antennas do not present strong rejection in the out-of-band region. Moreover, most of them present only one output, where the signals received in all desired bands are present. For navigation systems, circularly polarized (CP) antennas with high polarization purity should be employed in order to reduce the positioning errors caused by multi-path. One way to obtain CP microstrip antennas is by using geometry-perturbation techniques, which is effective only for very narrow-band applications. One of the drawbacks is that the CP purity is strongly dependent on the fabrication tolerances. Another way is by designing microstrip patches that operate with two orthogonal modes simultaneously and with its outputs connected to power splitter that introduces a 90° phase shift between its two outputs. For dual-band CP antennas, this splitter is normally optimized at a frequency between both desired bands. For this reason, the CP purity of the antenna is not optimum in the bands of interest, since the performance of the splitter degrades for frequencies other than the one for which it has been optimized. This paper presents a novel microstrip antenna capable of separating the E5A-E5b and the L1 bands of the European Galileo system in two different isolated ports. With this feature, one 90°-hybrid is needed in each port to receive right-handed circularly polarized (RHCP) waves in each of the aforementioned bands. For this reason, the hybrids can be optimized to operate in the center frequency of each band, hence resulting in an improvement of the axial ratio. Moreover, since the antenna separates already the signals received at each frequency band, the two bands can be processed separately already right after the antenna. Since no diplexer is needed to separate the signals received in the E5a-E5b and L1 bands, volume, weight and cost are reduced in comparison to conventional solutions. In the final version of the paper, the geometrical details of the proposed antenna will be depicted. Simulated and measured results will be shown and discussed. The simulations performed up to now show that the radiation pattern presents nearly the same shape in the two frequency bands of interest. Moreover, due to a proper selection of the employed dielectric materials, the radiation pattern obtained is broad, which is important for receiving the signals coming from satellites passing near the horizon. At the zenith (90° of elevation), the simulations showed that the antenna presents a gain larger than 4 dBi. For an elevation angle of 5°, the computed gain is larger than -5 dBi. Further details about this antenna will be discussed in the final paper and in the conference

Dual-band antenna with highly isolated outputs for global navigation satellite systems receivers

This study describes the design of a dual-band microstrip antenna with four isolated outputs. The proposed antenna has been optimised to operate in the E5a/E5b and E1 bands of the European satellite navigation system Galileo. Each pair of outputs delivers the signal in only one of the operating bands; hence the antenna operates also as a diplexer. The operation principle, the design procedure and measured results are presented and discussed. It is demonstrated by means of measured results that the designed antenna exhibits high isolation between its output ports and that good performance in terms of radiation pattern and polarisation purity was obtained.Peer ReviewedPostprint (published version

Characterization of pharmaceuticals using Terahertz Time Domain spectral-tomography

In this paper a Terahertz T ime-Domain measurement system has been used to perform Tomographic imaging of pharmaceutical compounds with coating. Measurements on paracetamol and ibuprofene samples are done both in transmission and reflection geometries and their capabilities are compared. Results of the contrast reconstructions provide information of the relative permittivity of the pharmaceutical compounds. T he interfaces between materials with different permittivities are detected, thus allowing characterization of different layers of the compound.Peer ReviewedPostprint (published version