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The use of a low profile, light weight and easy to fabricate transpolarising surface placed on one side of a trihedral corner reflector (TCR) as polarimetric calibrator is presented in this letter. The transpolarising-TCR (TTCR) presents a high backscattered cross-polar response contrary to standard TCRs. The performance of this device has been tested at X-band using the UPC GB-SAR., Comment: Accepted for publication in IEEE Geoscience and Remote Sensing Letters

A metamaterial spacer to decorrelate two closely spaced antennas has been designed and tested. The metamaterial spacer exhibits an artificial magnetic conductor (AMC) behavior around 2.6 GHz. Its performance has been checked against a simple metal spacer (PEC), providing a quasi orthogonal radiation pattern and good results in terms of decoupling and decorrelating a two-antenna system. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1414–1417, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23365

The use of a transpolarizing surface placed on one side of a trihedral corner reflector (TCR) as polarimetric calibrator is presented in this paper. The transpolarizing-TCR presents a high back-scattered cross-polar response. This structure has been tested at 9.65 GHz (X-band) with the help of the UPC GB-SAR system.

Conventional antenna radiation efficiency measurement techniques, such as the Wheeler cap, are generally narrow-band and, thus, well suited for resonant antennas. In this work, the Johnston-Geissler (J-G) method based on the Wheeler cap principle is used in a wide frequency range. First, a good agreement between measurement and simulation in an ultrawide frequency band is shown on a straight wire monopole antenna with different attenuators emulating antenna losses. Then, this technique is used to measure the radiation efficiency of several ultrawideband (UWB) antennas.

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.

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.

Artificial Magnetic Conductors (AMCs) offer many reflecting applications. When non symmetrical elements (diagonal slots, offset vias) are used, a cross-polar reflected response is achieved given an incident copolar electric field. This electromagnetic property can be used for polarisation conversion or RCS reduction purposes. A cross-polarising surface composed of square patches and diagonal slots over a ground plane has been designed and measured, providing good results for normal incidence. (4 pages)

A novel transpolarizing or crosspolarizing surface has been proposed to be applied in polarimetric SAR calibrating systems, like trihedrals, since they can not provide initially a crosspolar response. So the trans-surface has been designed and measured in an anechoic chamber, providing good results for normal incidence.

The AMC behavior of a reflecting surface is mainly related to the frequency where the 0deg crossing in the phase of its reflection coefficient takes place. This frequency gives the resonant frequency that characterizes the AMC surface. Two different designs of AMC surfaces showing quite different properties are presented in this communication. A first design proves the AMC behavior using metallic tubes with slotted square profile instead of the typical periodic arrangement of strips printed on a dielectric substrate; and the latter, shows the AMC performance of an artificial material when the electromagnetic waves impinge on its opposite faces.

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.

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 /spl 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 /spl lambda//4 distance and by placing the antenna close to the AMC. This latter solution is lower profile.

The surface current distribution of a Sierpinski fractal antenna shows a self-similar behaviour determined by the self-similar properties of its geometry. The application of infra-red thermography to electromagnetic near field detection allows the experimental verification of the active region scaling of a fractal antenna operating at different bands.

Experimental verification of the fractal Sierpinski antenna surface current distribution is presented. Measured data from an infrared camera agree with numerical data showing a self-similar behavior in the current density distribution over the fractal antenna surface. This result gives a better insight on the multiband behavior of the fractal-shape antenna.

Electromagnetic fields close to radiant structures can be measured quickly using an infrared camera. Examples of induced fields by wire antennas over a detection screen at distances shorter than one wavelength are presented. The measured thermograms agree with simulations that take into account heat propagation on the detection screen.

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. Broadband phase shifters and Wilkinson power combiners are used to generate the required circular polarization.

We consider an UWB scatterer imaging technique for determining the most significant positions of scatterers and reflection coefficients, in order to characterize the channel in terms of impulse response. We use two focused orthogonally aligned arrays, where transmitter and receivers have known positions.