R. Gonzalo

Thin AMC Structure for Radar Cross-Section Reduction

A thin artificial magnetic conductor (AMC) structure is designed and breadboarded for radar cross-section (RCS) Reduction applications. The design presented in this paper shows the advantage of geometrical simplicity while simultaneously reducing the overall thickness (for the current design ). The design is very pragmatic and is based on a combination of AMC and perfect electric conductor (PEC) cells in a chessboard like configuration. An array of Sievenpipers mushrooms constitutes the AMC part, while the PEC part is formed by full metallic patches. Around the operational frequency of the AMC-elements, the reflection of the AMC and PEC have opposite phase, so for any normal incident plane wave the reflections cancel out, thus reducing the RCS. The same applies to specular reflections for off-normal incidence angles. A simple basic model has been implemented in order to verify the behavior of this structure, while Ansoft-HFSS software has been used to provide a more thorough analysis. Both bistatic and monostatic measurements have been performed to validate the approach.

Electromagnetic bandgap antennas and components for microwave and (Sub)millimeter wave applications

This paper reviews the primary application areas of electromagnetic bandgap (EBG) technology at microwave and (sub)millimeter wave frequencies. Examples of EBG configurations in the microwave region include array antennas, high precision GPS, mobile telephony, wearable antennas and diplexing antennas. In the submillimeter wave region a 500 GHz dipole configuration and a novel heterodyne mixer is shown for the first time. Some emphasis is also placed on EBG waveguides and filters. As most fundamental components will be available in EBG technology, a fully integrated receiver could be developed in order to take full advantage of this technology. True integration of passive and active components can now begin to materialise using EBG technology.

Measurement of the dielectric constant and loss tangent of high dielectric-constant materials at terahertz frequencies

Low-loss high dielectric-constant materials are analyzed in the terahertz frequency range using time-domain spectroscopy. The dielectric constant and loss tangent for steatite, alumina, titania loaded polystyrene, and zirconium-tin-titanate are presented and compared to measurements on high-resistivity silicon. For these materials, the real part of the dielectric constant ranges from 6 to 90. All of the samples were found to have reasonable low-loss tangents. Applications as photonic crystal substrates for terahertz frequency antenna are envisaged.

Improved patch antenna performance by using photonic bandgap substrates

In this letter, a patch antenna on a photonic bandgap substrate is presented. A reduction in the leel of surface-wae mode excitation has been obtained. This leads to improed efficiency, gain, and far-field radiation pattern. Furthermore, improements in the input return loss hae been reported. Q 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 213)215, 2000.

A low-cost fabrication technique for symmetrical and asymmetrical layer-by-layer photonic crystals at submillimeter-wave frequencies

This paper presents a rapid, versatile, and practical technique for the manufacture of layer-by-layer photonic crystals in the millimeter- and submillimeter-wave regions. Mechanical machining is used to derive a rugged layer-by-layer structure from high-resistivity silicon wafers. Unlike traditional anisotropic etching techniques, this method does not rely on any particular crystal orientation of the substrate and allows greater flexibility in the photonic crystal design. Automatic alignment of alternating layers is achieved via careful placement of the separation cuts. Using this ability, two configurations of photonic crystals are realized and their RF characteristics are measured and presented. Firstly, a symmetrical photonic crystal is studied as an initial demonstration of the technique. This is followed by an asymmetrical example, where a different frequency response is observed for the two orthogonal polarizations of the incident radiation. Two measurement techniques are used to characterize the photonic crystals and the merits of each are discussed. Theoretical predictions are seen to agree well with the measured behavior.

Manufacturing Tolerance Analysis, Fabrication, and Characterization of 3-D Submillimeter-Wave Electromagnetic-Bandgap Crystals

The sensitivity of the characteristic band edge frequencies of three different 500-GHz electromagnetic-bandgap crystals to systematic variations in unit cell dimensions has been analyzed. The structures studied were square bar woodpiles made with dielectric having epsiv rap12 and epsivr=37.5 and two wide bandgap epsivr=37.5 crystals designs proposed by Fan and Johnson and Joannopoulos. These epsivr values correspond to high-resistivity silicon and a zirconium-tin-titanate ceramic, respectively. For the woodpiles, the fractional frequency bandgap varied very little for dimensional deviations of up to plusmn5% from the optimum. The bandgaps of the Fan and Johnson and Joannopoulos structures were affected to a greater extent by dimensional variations, particular sensitivity being exhibited to the air-hole radius. For all crystals, the effect of increasing the amount of dielectric in the unit cell was to shift the bandgap edges to lower frequencies. Both silicon and ceramic woodpiles, along with a ceramic Fan structure, were fabricated and dimensionally characterized. Mechanical processing with a semiconductor dicing saw was used to form the woodpiles, while the Fan structure required both dicing and UV laser drilling of circular thru-holes. Good agreement with predicted normal incidence transmissions were found on the low-frequency side of the bandgap in all cases, but transmission values above the upper band edge were lower than expected in the ceramic structures

Magnetotunable left-handed FeSiB ferromagnetic microwires.

The magnetotunable left-handed characteristics of Fe(77.5)Si(12.5)B(10) glass-coated ferromagnetic microwires are analyzed in array and single microwire configuration, employing a rectangular waveguide working in X band. While the negative permeability is ascribed to the natural ferromagnetic resonance (NFMR) of the highly and positive magnetostrictive microwire, the negative permittivity features of the medium are attributed to the interaction of the microwires with the metallic rectangular waveguide. The dependence of the NFMR frequency on the applied external magnetic field enables the design of magnetotunable left-handed systems with wide-frequency band.

A Metamaterial T-Junction Power Divider

A metamaterial based compact microstrip T-junction power divider working at 10GHz is proposed. The metamaterial unit cell consists of microstrip gaps and via holes whose behavior is equivalent to the combination of series capacitors and shunt inductors respectively, that is, a dual transmission line (high-pass) configuration. By adjusting the parameters of these structures, the characteristics of the Metamaterial-medium can be set to achieve a desired phase shift. To validate the design, a T-junction power divider is fabricated and measured. A 70% reduction of the length of the impedance transformer, without significant performance degradation, has been achieved

Electromagnetic-Bandgap Waveguide for the Millimeter Range

This paper presents the design, manufacturing, and characterization of a waveguide based on electromagnetic-bandgap (EBG) technology working in W-band. A modified silicon EBG woodpile structure was used in order to improve the matching performance of the EBG waveguide to a standard rectangular waveguide. The transition between the silicon EBG woodpile waveguide and the conventional WR10 waveguide was optimized and a 13.5% bandwidth around 90 GHz was achieved. The measured insertion losses remained better than 3 dB in the overall working bandwidth.

EBG Superstrate for Gain Enhancement of a Circularly Polarized Patch Antenna

EBG enhanced antennas could advantageously replace conventional array antenna in Geo-synchronous global Earth coverage applications at S-band and lower frequencies. This new technology simplifies the antenna configuration and can potentially lead to lighter and cost effective solutions, by either eliminating or strongly simplifying the antenna beam forming network (BFN). Excellent agreement between the predictions and the measurements has been shown