Andreea Hadarig

Submillimeter-Wave Frequency Scanning System for Imaging Applications

A new submillimeter-wave imaging system based on the frequency scanning concept is presented. Using significantly less information than beam-steering techniques, frequency scanning-based imaging systems are able to provide angular information in range-based radar systems which do not allow mechanical or electronic beam steering. Several strategies have been adopted to overcome the low dynamic range due to the propagation losses and non-specular reflection on the object-under-test. Moreover, the system is not only capable of detecting the placement of the objects, but also their profile. In this sense, an imaging application showing the system capabilities for the detection of objects concealed under clothes is presented. Results using 1-D FSAA allowing profile imaging are shown, proving the validity of the proposed system.

Millimeter Wave Subharmonic Mixer Implementation Using Graphene Film Coating

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 fllm coating. The circuit structure is made up of various fllters, 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.

Frequency scanning slotted waveguide in the sub-millimeter wave band

In this work, a waveguide slotted antenna array working in the sub-millimeter wave band is presented. The antenna performs beam tilting from 68 to 89 degrees in the H-plane while sweeping the frequency from 240 GHz to 310 GHz. Sixteen rectangular slots have been cut in the wide surface of a standard WR-3 brass metal rectangular waveguide to obtain the desired behavior. The antenna has been fabricated combining laser and mechanical prototyping machinery. Experimental results showing the main waveguide slotted antenna array characteristics are also presented.

High-Order Subharmonic Millimeter-Wave Mixer Based on Few-Layer Graphene

A millimeter-wave subharmonic-mixer topology based on a few-layer graphene component has been designed, manufactured, and experimentally characterized. The circuit has been conceived to perform the up/downconversion of a signal in the WR-3 band, between 220-330 GHz, using a high-order harmonic component of the input signal in the WR-28 band, between 26.5-40 GHz, as a local oscillator. The manufactured prototype has been characterized in both upconversion and downconversion, for the subharmonic orders between 5-14, obtaining a peak conversion gain value over -65 dB. The theoretically predicted capability of graphene to produce high-order intermodulation products at millimeter-wave frequencies, with a slowly decaying amplitude pattern, has been experimentally verified.

Millimetre wave textile integrated waveguide beamforming antenna for radar applications

In this work, a fully Textile Integrated Waveguide (TIW) beamforming antenna for its use in a radar system operating at 77 GHz is presented. The TIW beamforming antenna is based on a Substrate Integrated Waveguide (SIW) slot antenna array and it is designed to be manufactured completely with conductive and non-conductive threads using industrial textile machinery, avoiding subsequent sewing and adhesive processes for its integration in wearable or comformable systems. The antenna performs beam tilting from 11 to 23 degrees in the H-plane while sweeping the frequency from 70 GHz to 77 GHz. Firstly, a design of the equivalent SIW beamforming antenna structure is simulated and optimized and then, the translation into a fully woven TIW beamforming antenna structure is presented. The proposed TIW beamforming antenna design is provided with a TIW to WR10 standard rectangular waveguide transition for its experimental validation.

Millimetre wave imaging system for the detection of hidden elements in artwork

In this work, a millimetre/sub-millimetre wave imaging system for the analysis, characterisation and detection of hidden elements in artwork is presented. The practical implementation of the system relies on a novel generation of purpose developed frequency multiplier and mixer topologies, based on graphene non-linear devices. The proposed set-up will be experimentally validated by scanning a model painting, in order to practically illustrate the imaging capabilities of the system.

Novel parametric electromagnetic modelling to simulate Textile Integrated Circuits

In this work, a parametric electromagnetic (EM) modelling to develop Textile Integrated Circuits (TIC) is presented. Due to the necessity of having an accurate model to design TIC, avoiding the simulation of every filament which forms each yarn, a three-step characterisation of textile structures has been carried out. First, an ideal non-deformed model of the textile structure is represented, taking into account every filament which forms each yarn, when using multifilament threads. This model would then be adjusted depending on the different forces working between the yarns modifying the distribution of the filaments and deforming the yarns. Secondly, an EM equivalent model of the structure is presented, which is formed by monofilaments with the deformed cross section. This equivalent second model is easier to work with and its simulation is more efficient in terms of computational resources. Finally, an equivalent three-layer EM model is presented, which corresponds to the conventional simulation of substrate integrated circuits. The three models are electromagnetically equivalent and allows the user to simplify the TIC simulation process.

3D printed millimeter wave receiver integrating a graphene subharmonic mixer and a diagonal horn antenna

This work presents a millimeter/submillimeter wave frequency receiver integrating a graphene subharmonic mixer and a diagonal horn antenna. The device receives the RF signal through the diagonal horn antenna directly connected to the WR-3 input of the mixer. The desired frequency mixing performance is obtained using the non-linear behavior of a few-layer graphene film placed on a microstrip line gap. Using the internally generated 6th, 8th and 10th harmonic components of the input signal provided by the WR-28 standard waveguide in the 26-40 GHz the downconversion operation of the RF signal to a 300 MHz intermediate frequency is performed. A prototype of the receiver has been manufactured using high precision 3D printing technology. The performance of this device is characterized taking into account the behavior of the IF power in the 220-330 GHz band. Measured radiation patterns are also included.

Millimetre wave receiver based on a few-layer graphene WR-5 band subharmonic mixer

In this work, a millimetre wave receiver prototype integrating a graphene based subharmonic mixer and a diagonal horn antenna is presented. The block receives a millimetre wave signal in the WR-5 frequency band (140-220 GHz), which is downconverted using a high-order harmonic component of the local oscillator signal, in the WR-28 frequency band (26.5-40 GHz), producing an IF output at 300 MHz. A prototype has been manufactured using high precision 3D printing techniques. The performance for subharmonic orders 6, 8 and 10 has been evaluated through preliminary measurements in the neighbouring WR-3 frequency band. Measured radiation patterns are also presented.

7 th order sub-millimeter wave frequency multiplier based on graphene implemented using a microstrip transition between two rectangular waveguides

In this work, a 7th order sub-millimeter wave frequency multiplier for Terahertz applications is presented. The multiplier is based on a microstrip line with a small gap where a graphene film layer is deposited. The multiplication phenomena is reached via the nonlinear behavior of the graphene film using an input signal provided by the WR28 standard waveguide operating in the Ka frequency band (31 to 40 GHz). A prototype of the multiplier has been manufactured and the behavior of the output power in the 220-280 GHz band versus the input power has been experimentally characterized.