J.M. Gonzalez-Arbesu

Are space-filling curves efficient small antennas?

The performance of space-filling curves used as small antennas is evaluated in terms of quality factor and radiation efficiency. The influence of their topology is also considered. Although the potential use of these curves is for antenna miniaturization, their behavior is not exceptional when compared with other intuitively generated antennas.

Comparison of Antenna Measurement Facilities With the DTU-ESA 12 GHz Validation Standard Antenna Within the EU Antenna Centre of Excellence

The primary objective of many antenna measurement facilities is to provide a specified high accuracy of the measured data. The validation of an antenna measurement facility is the process of proving that such a specified accuracy can be achieved. Since this constitutes a very challenging task, antenna measurement accuracy has been the subject of much research over many years and a range of useful measures have been introduced. Facility comparisons, together with antenna standards, error budgets, facility accreditations, and measurement procedure standards, constitute an effective measure towards facility validations. This paper documents the results of a comparison between 8 European antenna measurement facilities with a specially designed reference antenna, the DTU-ESA 12 GHz validation standard antenna (VAST-12). The electrical and mechanical properties of the VAST-12 antenna are presented and its three different coordinate systems are defined. The primary objective of the comparison is to obtain experience and results that can serve to develop standards for validation of antenna measurement facilities. The paper focuses on the comparison of the radiation pattern and presents not only the measurement data obtained at the facilities, but also investigates several procedures for comparing these data. This includes various definitions of pattern difference and statistical measures as well as a reference pattern. The comparison took place in 2004-2005 as part of the European Union network of excellence called ACE-Antenna Centre of Excellence.

GA design of wire pre-fractal antennas and comparison with other Euclidean geometries

A multi-objective genetic algorithm (GA) has been applied in conjunction with the numerical electromagnetic code (NEC) to the optimization of wire pre-fractal Koch-like antennas in terms of bandwidth, efficiency, and electrical size. Their performance is compared to that of other nonfractal designs.

Concentric Annular-Ring Microstrip Antenna With Circular Polarization

In this letter, we present a concentric annular-ring microstrip antenna that covers the bands of Galileo (E5a, E5b, E1, E2, L1), GPS (L1, L2, L5), and GLONASS (L1, L3). This microstrip antenna is fed by four apertures that improve the coupling. Broad band phase shifters and Wilkinson power combiners are used to generate the required circular polarization.

Transpolarizing Surfaces and Potential Applications

Transpolarizing surfaces are characterized for their property of rotating by 90deg the reflected electric field with respect to the incident one. Several transpolarizing surface designs are presented, and their potential applications and limitations, mostly for oblique incidence, are discussed.

Broadside radiation enhancement using a spiral resonator MNZ metamaterial substrate

The broadside power radiation enhancement has been tested for the case of a magnetic dipole in presence of an MNZ metamaterial substrate. In order to assess the theoretical estimations, a slot antenna on a ground plane has been fabricated and an AMC composed of 1 layer square spiral resonators has been used as an MNZ metamaterial slab. The radiation patterns have been measured in the anechoic chamber, achieving a gain in directivity of more than 1 dB. However, it should be taken into account that the thickness of the fabricated metamaterial slab (6 mm) is much smaller than the theoretical optimum thickness (hundreds of mm). The directivity of the antenna might be improved when increasing the number of layers of the metamaterial slab; in fact, in such a case, the leaky waves responsible of directive radiation are expected to be more significantly excited giving rise to the sought broadside power enhancement.

Design and measurement of a spiral-cell PMC for metamaterial applications

Simulations and measurements have been carried out of a 1-layer metamaterial slab made of spiral resonators that shows an AMC behavior, with an equivalent electrical width of lambda/12 for the thickness (z dimension) of the slab. This behavior has been experimentally verified through radiation pattern measurements. The results show that similar results are obtained by placing a PEC at a lambda/4 distance and by placing the antenna close to the AMC. This latter solution is lower profile

Application of UWB antenna descriptors to lossy dipole performance assessment

This paper proposes to characterize antennas for UWB applications, considering the transmitter-receiver system, using figures of merit that do not depend on direction. From the basic formulation for a single antenna we extend this concept to a system containing transmit and receive antennas. We use these parameters to optimize dipole design with respect to its conductivity

Artificial magnetic reflector based on spiral resonators

An artificial magnetic reflector is built based on squared spiral resonators. Numerical simulations using efficient MLMDA (multilevel matrix decomposition algorithm) techniques are used for designing the reflector and the antenna. Measurements of the reflection coefficient of the artificial screen are carried out in order to verify the viability of the proposal. The performance of the reflector in combination with a folded dipole as an active element is also evaluated.

Transpolarizing Trihedral Corner Reflector Characterization Using a GB-SAR System

The use of a low-profile, lightweight, and easy-to-fabricate transpolarizing surface placed on one side of a trihedral corner reflector (TCR) as a polarimetric calibrator is presented in this letter. The transpolarizing TCR presents a high backscattered cross-polar response contrary to standard TCRs. The performance of this device has been tested at the X-band using the Universitat Politecnica de Catalunya ground-based synthetic aperture radar.