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A three-dimensional fully interlaced woven microstrip-fed substrate integrated waveguide has been designed, manufactured and experimentally validated. The waveguide has been conceived based on the conventional substrate integrated waveguide (SIW) technology and works in a range of frequencies between 7.5GHz and 12GHz. The SIW structure is suitable to be translated into different equivalent woven structures depending on the characteristics of the employed threads, as it has been presented in previous works. In this work, a structure based on rigid weft threads has been employed with the aim of translating both the waveguide and the corresponding SIW to microstrip transitions, into woven patterns and, therefore, achieving the main purpose of a complete integration of the circuit into the textile, avoiding the use of external transitions for its validation. Consequently, three prototypes, using three different lengths, have been manufactured and experimentally characterised, and the theoretically predicted behaviour of the prototypes has been experimentally verified. [ABSTRACT FROM AUTHOR]

A flexible fully textile-integrated bandstop frequency selective surface working at a central frequency of 3.75GHz and presenting a 0.6GHz bandwidth has been designed, manufactured and experimentally characterised. The frequency selective surface consists of a multilayered woven fabric whose top layer presents periodic cross-shaped conductive resonators, and due to its symmetries, its performance is largely independent of polarisation and angle of incidence. These properties make the prototype very interesting for shielding applications. The designed frequency selective surface is based on a layer-to-layer angle interlock 3D woven fabric. This technology provides the prototype with flexibility, portability and the possibility of manufacturing it in a large scale production by the use of existing industrial weaving machinery, in contrast to conventional frequency selective surfaces manufactured using rigid substrates. The proposed textile frequency selective surface has been simulated and experimentally validated providing good agreement between the simulations and measurements. The measured maximum attenuation has been found to be higher than 25 dB under normal incidence conditions. [ABSTRACT FROM AUTHOR]

In this work, reflectarray antennas are proposed for their use as probes in compact antenna test ranges. For that purpose, the quiet zone generated by a single offset reflectarray is enhanced, overcoming the limitation imposed by the amplitude taper of the feed antenna. First, the near field is characterized by a radiation model which computes the near field of the reflectarray as far field contributions of each element, which are modeled as small rectangular apertures and thus taking into account the active element pattern. Then, a phase only synthesis is performed with the Levenberg- Marquardt algorithm in order to improve the size of the generated quiet zone. Due to the nature of the application, this near field synthesis takes into account both the amplitude and phase, making it a more challenging task than an amplitude-only synthesis. The optimization is focused on flattening the amplitude while trying to preserve the phase front generated by the reflectarray. [ABSTRACT FROM AUTHOR]

In this work, a subharmonic frequency mixer for millimeter wave applications has been designed. The mixing and multiplication phenomena are simultaneously achieved via a nonlinear component consisting in a microstrip line gap covered by a graphene film coating. The circuit structure is made up of various filters, which have been optimized to ensure high port-to-port isolation. The nonlinear behavior of the subharmonic frequency mixer has been experimentally evaluated within the 39-40.5GHz RF frequency band. The frequency downconversion is achieved by mixing the RF signal with the second harmonic component of a 17.9GHz LO signal. Conversion losses are minimized by generating a return path for IF, through the use of a quarter wavelength open-ended stub. [ABSTRACT FROM AUTHOR]

In this work a non-linear efficiency optimization method for its application to an Injection-Locked High Efficiency Voltage Controlled Oscillator is presented. The proposed approach is based on the control of the harmonic content of the oscillator autonomous signal, which is accomplished through the use of an Auxiliary Generator and several multi-harmonic loads based on Arbitrarily Width-Modulated Microstrip Lines. The presented technique has been applied to the design of a 2.5GHz high efficiency Voltage Controlled Oscillator, which has been manufactured and experimentally characterized, obtaining a good agreement between the simulated and measured results. [ABSTRACT FROM AUTHOR]

Contour reconstruction and accurate identification of dielectric objects placed on a conducting surface are the aims of the millimeter-wave Synthetic Aperture Radar (SAR) imaging processing system presented in this paper. The method uses multiple frequencies, multiple receivers and one transmitter in a portal-based configuration in order to generate the SAR image. Then, the information in the image is used to estimate the contour of the body under test together with the permittivity of the dielectric region. The results presented in this paper are based on synthetic scattered electromagnetic field data generated using an accurate Finite-Difference Frequency-Domain (FDFD)-based model and inversion based on a fast SAR inversion algorithm. Representative examples showing the good behavior of the method in terms of detection accuracy are provided. [ABSTRACT FROM AUTHOR]

The design and evaluation of an active three dimensional (3D) millimeter wave imaging system for personnel security screening is presented in this work. The system is able to produce a high-resolution 3D reconstruction of the whole human body surface and reveal concealed objects under clothing. Innovative multistatic millimeter wave radar designs and algorithms, which have been previously validated, are combined to significantly improve the previous reconstruction results. In addition, the system makes use of a reduced amount of information, thus simplifying portal design. Representative simulation results showing good performance of the proposed system are provided and supported by sample measurements. [ABSTRACT FROM AUTHOR]