Regis Guinvarc'h

A 6:1 Bandwidth, Low-Profile, Dual-Polarized Ring Array of Spiral Antennas With Connecting Arms

In an earlier work, the design of a 2:1 bandwidth dual-polarized phased array of Archimedean spiral antennas with cavity was presented. The reflection coefficient, circular polarization, and grating lobes goals were obtained independently in the design process. The low end of the final bandwidth was constrained to the frequency cutoff of the spiral antenna, at the low end of its bandwidth. In this communication, an extension of the bandwidth of the array is achieved by connecting the spiral antennas of the array. Hence, with the same size, the bandwidth is enlarged almost three times (a total of 6:1). The measurements confirm the simulations. The array can scan up to θ = 30° keeping a low reflection coefficient, good right- and left-hand circular polarization, low-sidelobe levels, and using a low-profile cavity.

Genetic algorithm optimization of a dual polarized concentric ring array

We use a genetic algorithm to minimize the Relative Sidelobe Level (RSLL) of a dual polarized concentric ring array. The optimization variables are the placement of uniformly weight spiral antennas in an aperture with a small area. We used isotropic sources for the optimization and the topology used is the concentric ring array. The computation of the Array Factor (AF) of the topology used is expensive and many function calls are required during the optimization, so we developed approaches to obtain a faster cost function and reduce the number of function calls.

The signature of rotated double bounces in urban areas

In radar remote sensing, classification of urban areas using SAR images is based on the following assumption: there is a dominant scattering mechanism, that is a dihedral-type mechanism. This assumption, widely accepted in the community, is clearly justified by the geometry of urban areas. However, it is noted that most of the results rely on this reference object, that is the perfectly oriented and metallic dihedral. We present here, from an electromagnetic point of view, what happens when the dihedral is disoriented and then we propose a compensation of this effect.

A simple pattern correction approach for high frequency surface wave radar on buoys

The concept of floating antenna array is to replace a conventional coastal receive unit by a sea floating array, constituted of a set of receive buoys. Waves and wind introduce movements of buoys in the array which generate disturbances in the radiation pattern. In this paper, compensation methods for vertical and longitudinal displacements are presented. This document introduces algorithms for both compensation methods. Then, these algorithms are combined in series, providing a simple model method to optimize the radiation pattern of the deformed array.

Cross-Polarization Amplitudes of Obliquely Orientated Buildings With Application to Urban Areas

Buildings that are rotated with respect to the sensor trajectory could be erroneously classified as vegetated areas in the Pauli basis, and subsequently in many decomposition theorems despite the considerable amount of work done to solve that issue. This misjudgement is linked to the high level of their cross-polarized contribution. Using electromagnetic simulation tools and image analysis, we study the value of these cross-polarization components. We show that forested areas and cities exhibit significantly different cross-polarization levels; indeed, the origin of these components is actually distinct. Based on that, to discriminate between the two environments, we introduce an extension to the Pauli basis where the cross polarization is split into two classes, one for rotated dihedrals and the other for random scatterers. This approach is then tested on two synthetic aperture radar images: the first acquired at C-band using RADARSAT-2 over Downtown San Francisco and the second using RAMSES at X-band over an industrial area near Paris.

Phase error analysis of a dual polarized concentric ring array

In a previous work a dual-polarized non-uniform concentric ring array of spirals has been developed. This array used the sequential rotation technique as a means to enhance the arrays axial ratio and the non-uniform concentric rings to reduce the relative side lobe level. In the present paper the effects of realizing the phases of the sequential rotation using digital phase shifters are analyzed, considering both the phase-quantization and the phase-error effects in the broadside radiation of the array. We show that by considering a 2-bit phase shifter with a centered Gaussian error (sigma=5°) in each element of the array the axial ratio is kept under 1dB over the whole bandwidth, with a maximal degradation of 0.85dB when compared with the array without phase-errors or phase-quantization. We also show that the side lobe level suffers a maximal degradation of 4dB for the 2-bit phase shifter, however it is not affected by the phase error.

Optimizing communication in TMA for radar

A Time Modulated Array (TMA) based technique is used to simultaneously do a radar function in the main lobe and a communication function in the side lobes. It uses an averaging to do the radar function, while the communication is done with the variation from an intermediary pattern to another. An optimization of the secondary function (communication) is carried out. The QAM communication is optimized for the case of STMA.

Large bandwidth analysis in multifunction antenna for radar and communication applications

Large bandwidth analysis of the communication function for a single antenna system providing simultaneously radar and communication functions is studied. The system is composed of a slotted waveguide (for the communication function) feeding a horn antenna (for the radar function) so as to assign to each function different polarizations. Additionally, by switching between two slot arrays on the waveguide, a BPSK communication is achieved independently of the horn radiation.

Low frequency bandwidth in connected spiral arrays

Connecting the arms of spirals in a dual circularly-polarized array significantly increases the array bandwidth. The connections decreased the low frequency cutoff from 1 GHz (without connections) to 350 MHz of the original array without connections (1 GHz). In this paper, an analysis at even lower frequencies is carried out revealing that the array is still useful at the original low frequency cutoff divided by 10 (100 MHz).