This work was supported by the Spanish Ministerio de Ciencia e Innovacion through the CONSOLIDER-INGENIO 2010 program reference CSD2008-00068 TERASENSE.

In this contribution, the measurement procedure of the impedance and radiation characteristics of a cassegrain reflector antenna is presented. Near-field (NF) measurement techniques have been used to obtain the radiation pattern and the directivity of the antenna. The antenna efficiency has been characterized using a calibrated total power radiometer. Moreover, tolerance effects in the return loss (RL) measurements are discussed, providing a solution to overcome the variability of the input impedance of different antenna prototypes.

A near field imaging system for THz tomographic imaging based on a MST retina (an array of real antennas) has been designed. The main advantage of this implementation is the absence of microwave transmission line distribution networks and the capability to perform high speed imaging. The aim of this paper is to describe the design of the retina in order to maximize the performance of this imaging system.

This paper presents the characterization in terms of spatial resolution and radiometric sensitivity of a W-band Total Power Radiometer (TPR). The TPR is based on a heterodyne receiver with 64 dB of gain and 6.5 dB of noise figure. An antenna system consisting on a pan-tilt scanner has been designed and built in order to aim a 100 mm offset parabolic reflector. With this system, relative temperature images of targets at a 1 m standoff range are obtained in indoor environments with an spatial resolution of 4 cm.

In a tomographic imaging system, the key is to collect a sufficient number of scattered field points to recover the currents in the inverse scattering problem. This can be accomplished by using a real array of multiplexed antennas for real time imaging. In this paper, a W-Band Retina for Terahertz tomographic imaging is presented. A system based on a retina, a collector and an illuminator is described and the results of a fabricated retina are shown.

Interferometry at W Band can be exploited to form images of small deformations with precisions in the order of tenths of microns and retrieve surface relieves. An Interferometric Synthetic Aperture Radar setup is proposed in which the scattered field is focused using a combination of range compression and backpropagation algorithm. Interferometric images involving micrometric displacements have been obtained showing a good agreement between real and measured displacements. A metallic rough surface deformation test has been first performed, by imaging the phase difference between acquisitions before and after the displacement. The interferometric phase difference between acquisitions can be used to image local deformations from a range of several meters. Furthermore the interferogram coherence shows the degree of decorrelation of the radar reflectivity which provides valuable information for surface random change. Likewise the relief of the surface with an L-shape target is retrieved mapping the phase difference between the two receiving antennas, in this case an static scenario is required.

The measurement of scattered signals at W Band can be exploited to form images of small deformations with precisions in the order of tenths of micrometers. In this paper an Interferometric Synthetic Aperture Radar setup is proposed to form high resolution reflectivity images and deformation maps of dielectric or metallic surfaces. First, the system geometry of observation based on a linear motion of the radar antennas is described. A CW frequency domain measurement provides the wide band required for high resolution imaging. The scattered field data is focused on the surface spatial domain using a combination of range compression based on Inverse Fourier Transform combined with a backprojection algorithm to form the synthetic aperture with a high cross range resolution. The focusing performance has been assessed by numerical simulations and experimental measurements of simple scattering objects like spheres and trihedrals. Interferometric images of controlled displacements have been obtained showing a good agreement between real and measured displacements. A representative surface deformation test has been also carried out using a metallic rough surface. The interferometric phase difference between acquisitions can be used to image local deformations in the order of tens of micrometers from a range of several meters. Likewise the interferogram coherence shows the degree of decorrelation of the radar reflectivity which provides valuable information for surface random change assessment.

The design of a 94 GHz Total Power Radiometer system for imaging purposes is presented in this paper. A mechanical beam-scanning antenna system is used to acquire passive raster images. The main performance parameters of the imaging system are described as well as their impact on the resulting image quality. A temperature resolution below IK and a spatial resolution around 4 cm at 1 meter standoff distance are obtained with this system. Moreover, radiometric images acquired in indoor and outdoor environments are shown and compared.

A subsurface imaging system based on a terahertz time-domain spectrometer (THz-TDS) is described in this paper. The system performance has been simulated in terms of spatial resolution, penetration capabilities and SNR. Moreover, a commercial THz-TDS has been used to perform the proof-of-concept of the described system.

This work presents the main geometric constraints that affect the performance of a passive interferometer at 94 GHz for security screening applications by means of a reviewed definition of the Far Field condition in close range detection applications. This new approach allows to easily give, in a first order approximation, the number of antennas, the array size and the target range by using well known far field tools.

In this paper three different systems at 94 GHz for short-range imaging applications are presented; both active and passive methodologies are described. An analysis for each case is performed, determining the parameters which satisfy the field of view and resolution requirements. A T-shape interferometric radiometer is first exposed describing the implemented imaging algorithm, the overall system block diagram, and the images obtained from the simulations. The radiometric resolution estimate is calculated, specifying the minimum temperature the system is capable to detect in function of the system parameters. Then, a Mills-Cross based active system is presented; recovered images are shown, as well as the geometry employed in the setup performance. Finally, a reflectarray setup is described; presenting its geometry of exploration and operation principles. In addition a phase discretization analysis is performed for the case of 1 bit. For both active systems the minimum detectable Radar Cross Section, RCS, is computed.

In this paper, a comparison between both imaging techniques is performed with the aim of integrating both in a single imaging system. It is expected that the combination of the coherent and incoherent radiation in active and passive operation will offer improved detection and identification of concealed objects. An interferometric radiometer and an active mills-cross have been studied as near field imaging systems. The main parameters have been simulated to foresee their performance as image scanning systems. Moreover, a T-shape active imaging system has been built and measurements have been done in order to test and assess the performance of this imaging geometry.

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.

This chapter is intended for presenting the research carried out to find a radiating structure that fulfils all the requirements. In the following lines, a total number of 3 antenna structures are studied plus several other that will be just shown and ruled out because don’t achieve the objectives. This chapter also contains a basic theory to explain the behaviour of the antennas. With this theory it will be easier to understand the results obtained in the simulations as well as the special properties of each antenna.

This paper presents the design of two ground based synthetic aperture radar (GB-SAR) systems working at 94 and 300 GHz respectively. Frequency-modulated continuous-wave (FM-CW) technique is used for both systems, being described in the first section. Afterwards the first design at 94GHz is presented, explaining its geometry of exploration and describing the architecture of the W-band radar setup. Regarding the integrated receiver system, two models of low noise (LNA) and medium power amplifiers are disclosed, presenting noise figure and S parameters curves comprising frequencies between 75 and 110 GHz (W-band). Finally the second radar setup working at 300GHz is presented, depicting the hardware block diagram and explaining the main performance parameters of the system.