Fernando Las Heras Andres

A Novel Approach for RCS Reduction Using a Combination of Artificial Magnetic Conductors

A thin Artiflcial Magnetic Conductor (AMC) structure for Radar Cross-Section (RCS) reduction applications is presented. The manufactured prototype, which combines two unit-cell metallization sizes, presenting two resonant frequencies, shows broad AMC operation bandwidth, polarization angle independency, and its angular margin when operating under oblique incidence is also tested. It is shown that signiflcant RCS reduction can be achieved with the proposed AMCs combination even if a 180 - phaseshift between re∞ected waves is not met. Two designs are considered: the already mentioned design combining AMCs with overlapped frequency bands and the second one combining Perfect Electric Conductor (PEC) and AMC surfaces. A comparison between these two designs regarding RCS reduction, supported by measurements in an anechoic chamber, is presented.

MICROSTRIP ANTENNA DESIGN BASED ON STACKED PATCHES FOR RECONFIGURABLE TWO DIMENSIONAL PLANAR ARRAY TOPOLOGIES

In this work, a probe fed microstrip antenna design for the implementation of two dimensional arrays with individually fed radiating elements is presented. The performance of the antenna element, both isolated and in a 4 £ 4 flxed array topology, is analysed using ADS and HFSS simulation software. Prototypes of the antenna element and of the array are manufactured and measured for the experimental validation of the design.

MILLIMETER WAVE MICROSTRIP MIXER BASED ON GRAPHENE

In this work, a millimeter wave microstrip frequency-mixer design based on graphene is presented. The desired frequency mixing behavior is obtained using a nonlinear component consisting in a microstrip line gap covered by a graphene layer. The circuit includes microstrip fllters that have been designed to obtain a high isolation between the input and output ports. The nonlinear behavior of the frequency mixer has been experimentally evaluated in the 38.6{40GHz input signal frequency range, for difierent values of the input power and local oscillator power.

On the Comparison of the Spherical Wave Expansion-to-Plane Wave Expansion and the Sources Reconstruction Method for Antenna Diangostics

A comparison between two recently developed methods for antenna diagnostics is presented. On one hand, the Spherical Wave Expansion-to-Plane Wave Expansion (SWE-PWE), based on the relationship between spherical and planar wave modes. On the other hand, the Sources Reconstruction Method (SRM), based on the application of the equivalence principle and the integral equations relating fields and sources. In order to compare the results provided by these methods, a reflector antenna has been measured and analyzed.

Flexible Uniplanar Artificial Magnetic Conductor

A flexible uniplanar Artificial Magnetic Conductor (AMC) design is presented. FEM simulations used to design and analyze the performance of the AMC structure are shown. Its performance under flat and bent conditions is characterized by means of reflection coefficient phase measurements of a manufactured prototype in an anechoic chamber. Broad AMC operation bandwidth and polarization angle independency is found for the prototype in both flat and bent situations. In addition, its angular margin under oblique incidence operation is also measured.

On the Use of Improved Imaging Techniques for the Development of a Multistatic Three-Dimensional Millimeter-Wave Portal for Personnel Screening

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 signiflcantly 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.

Multi-Harmonic DC-Bias Network Based on Arbitrarily Width Modulated Microstrip Line

In this work, we present a novel DC-bias network for multi- harmonic microwave circuits based on an arbitrarily width-modulated microstrip line. The arbitrary shape of the width-modulated microstrip line is obtained by using multiple microstrip taper sections. The method is illustrated through the design of four difierent DC-bias networks blocking from 1 to 4 harmonic components of a 2.5GHz signal. The designs with an optimum shape for the arbitrarily width- modulated microstrip line have been manufactured and measured, obtaining a good agreement between the simulated and measured behavior.

On the Influence of Coupling AMC Resonances for RCS Reduction in the SHF Band

A novel approach to Radar Cross-Section reduction using a thin Artiflcial Magnetic Conductor (AMC) structure is presented. The novel AMC structure combines two unit-cell metallization sizes and so it presents two resonant frequencies. RCS reduction is based on destructive interference of two partial re∞ections. Taking as starting point a previous work showing signiflcant RCS reduction based on the combination of two AMC surfaces with overlapped AMC operation bandwidths (so that they have similar re∞ection coe-cient amplitude) without a 180 - -phaseshift, the key point of this contribution is to analyze the in∞uence of the degree of the aforementioned overlapping on RCS reduction and to show that this achievement is based on coupling phenomena. A comparison of the achieved RCS reduction when combining two AMCs whose AMC operation bandwidth overlaps, two AMCs with non-overlapped AMC operation bandwidths, and PEC-AMC is presented. Prototypes of these three combinations have been manufactured (having them the same size) and their RCS has been measured in an anechoic chamber.

Defected Ground Structure for Coupling Reduction between Probe Fed Microstrip Antenna Elements

The mutual coupling between elements of a microstrip antenna design based on stacked patches has been studied in an array conflguration. In order to mitigate the mutual coupling, a defected ground structure based on narrow, closely spaced rectangular slots has been proposed. Two arrangements with three and flve slots have been studied and optimised in an array conflguration with 0:7‚0 element separation. For the experimental validation of the simulated results, prototypes of two element antenna arrays with both DGS designs, as well as without DGS, have been manufactured and measured.

Optimization of the Synchronization Bandwidth of Rationally Synchronized Oscillators Based on Bifurcation Control

In this work, a nonlinear technique for the optimization of the synchronization bandwidth of Rationally Synchronized Oscillators (RSO) is presented. The circuit is forced to operate near a Hopf bifurcation point which is created around the frequency of the input reference signal. Under this operating regime, the reference signal is strongly amplified and the synchronization bandwidth of the circuit is considerably improved. A 5–3GHz rationally synchronized oscillator has been optimized using the proposed method. The manufactured RSO provides a 5 MHz synchronization bandwidth with a reference signal power of −22 dBm, in good agreement with simulation results.