Peter de Maagt

Broadband Radar Cross-Section Reduction Using AMC Technology

This paper presents the design, fabrication, and characterization of a planar broadband chessboard structure to reduce the radar cross-section (RCS) of an object. The chessboard -like configuration is formed by combining two artificial magnetic conductor (AMC) cells. The bandwidth limitations intrinsic to AMC structures are overcome in this work by properly selecting the phase slope versus frequency of both AMC structures. A 180 ° phase difference has been obtained over more than 40% frequency bandwidth with a RCS reduction larger than 10 dB. The influence of the incidence angle in the working bandwidth has been performed. A good agreement between simulations and measurements is achieved.

EBG enhanced feeds for high aperture efficiency reflector antennas

Typical feed horns can be lengthy and bulky, especially at low frequencies. This aspect alone constitutes a significant drive to nd alternative technologies, more suited to mass production, that can be used to obtain equally performing feeds. In particular it is useful to explore the possibility of using printed circuit board technology to upgrade the performances of a moderately sized (in terms of the wavelength) waveguide horn, so that the resulting feed can be used to efciently illuminate a reector antenna.

Resonance frequencies of cavities in three-dimensional electromagnetic band gap structures

This paper is devoted to the phenomenon of resonant transmission in three-dimensional electromagnetic band gap structures (EBGs), achieved by introducing a defect into an EBG structure with the corresponding resonance frequency of the defect lying within the initial EBG region. It is shown that the resonance frequency of an EBG air cavity (acceptor defect) can either increase or decrease with increasing cavity dimensions. In particular, this paper demonstrates both experimentally and theoretically that the resonance frequency of a woodpile air cavity, formed by the partial removal of a woodpile bar, increases with increasing cavity size; it increases continuously or saturates depending on the field polarization with respect to the cavity orientation. The results obtained in this paper can be used for designing EBG devices based on resonant transmission.

Terahertz technology for space and earth applications

Research has been carried out in the THz region for several decades. Until fairly recently, the main drive came from applications such as radio astronomy, later followed by planetary, cometary and atmospheric science. Arguably, without these driving influences it is unlikely that many of the recent technological breakthroughs would have occurred. This paper presents an overview of space and terrestrial related applications and technologies. The more traditional and some most likely future applications will be treated.

Design and Test of a 0.5 THz Dipole Antenna With Integrated Schottky Diode Detector on a High Dielectric Constant Ceramic Electromagnetic Bandgap Substrate

This paper presents the first analysis of the input impedance and radiation properties of a dipole antenna, placed on top of Fan s three-dimensional electromagnetic bandgap (EBG) structure, (Applied Physics Letters, 1994) constructed using a high dielectric constant ceramic. The best position of the dipole on the EBG surface is determined following impedance and radiation pattern analyses. Based on this optimum configuration an integrated Schottky heterodyne detector was designed, manufactured and tested from 0.48 to 0.52 THz. The main antenna features were not degraded by the high dielectric constant substrate due to the use of the EBG approach. Measured radiation patterns are in good agreement with the predicted ones.

Broadband Terahertz Analysis of Energetic Materials—Influence of Crystal Structure and Additives

A detailed broadband analysis of energetic materials using THz time-domain spectroscopy with a bandwidth from 0.2 to 6.4 THz is presented. Dependencies of the resonance features on different sample parameters are evaluated via spectroscopic investigation of several energetic materials (TNT, C4, RDX, PETN, AN) in transmission and reflection experiments. A strong dependency of the resonance features on the manufacturing process of an explosive is observed especially with TNT. The THz measurements of the TNT samples are compared to powder X-ray diffraction measurements. Furthermore, it is observed that additive compounds with a flat frequency response offset the THz reflection of an explosive, but the recognition capability of a resonance feature is not influenced.

Characterization of conductive textile materials for SoftWearAntenna

Transmission line measurements have shown a potential in characterization of conductive textiles for SoftWearAntenna applications. Decrease in the conductivity of the fabric is seen to decrease the propagation velocity of a wave. This is expected to have a lowering effect on the operation frequency of textile antennas based on conductive fabrics when compared with antennas utilizing copper as conductive elements.

Environmental characterization of industrial fabric for SoftWearAntenna

It was observed that changes in the environmental conditions have direct effect on the electrical parameters. High relative humidity increased the loss tangent. However, keeping the relative humidity constant while decreasing temperature, it was observed to decrease the loss tangent. It seems that the amount of water in the air controls the loss tangent; Decrease in temperature with constant relative humidity condenses some of the water vapor and thus the amount of water in the air is decreased. It was noticed that relative air humidity has a strong influence on permittivity. Increase in relative humidity was seen as an increase in permittivity and vice versa. Additionally, the temperature change affected the absolute value of permittivity. At lower temperatures the permittivity had lower values than at higher temperatures when the relative humidity remained fixed. Here, the absolute amount of water in the air seemed to be connected to this behavior as well.

CAD Techniques for 183GHz Fixed Tuned Sub-Harmonic Mixer Using Foundry Diodes

This paper describes the computer aided design techniques used to design millimeter-wave mixer components for potentially high volume applications such as medical and security screening and non-destructive testing. These are demonstrated by the design of a 183GHz subharmonic mixer for earth observation applications. Using commercially available foundry diodes, the mixer exhibits 6.85dB double side-band conversion loss and a mixer temperature of 988 Kelvin using 5mW of local oscillator power at 92GHz. The subharmonic mixer is designed as a fixed tuned component with the least number of parts to minimize the cost and maximize its potential for volume manufacture

Experimental demonstration of low Axial-Ratio Circular Polarization Selective Surface

The realization of a Circular Polarization Selective Surface (CPSS) exhibiting low Axial Ratio (AR) has been demonstrated experimentally in the X band, showing good agreement with the simulated response. The fabricated CPSS has been characterized using a free-space collimator system recently acquired by ESA. An AR below 1dB, which is comparatively smaller than previous results shown in the literature, has been achieved for more than 20% bandwidth.