Hervé Legay

A metallic Fabry-Perot directive antenna

We report the design of a directive antenna using the electromagnetic resonances of a Fabry-Perot cavity. The Fabry-Perot cavity is made of a ground plane and a single metallic grid. The resonance is excited by a patch antenna placed in the cavity at the vicinity of the ground plane. The two remarkable features of Fabry-Perot cavity antennas are, first, that they are very thin and second that only one excitation point is needed. A directivity of about 600 is measured at f=14.80 GHz which is to our knowledge one of the highest directivities reported for an antenna using Fabry-Perot resonances.

Dual-Polarization Dual-Coverage Reflectarray for Space Applications

A breadboard of a three-layer printed reflectarray for dual polarization with a different coverage in each polarization has been designed, manufactured, and tested. The reflectarray consists of three layers of rectangular patch arrays separated by a honeycomb and backed by a ground plane. The beam shaping for each polarization is achieved by adjusting the phase of the reflection coefficient at each reflective element independently for each linear polarization. The phase shift for each polarization is controlled by varying either the x or y patch dimensions. The dimensions of the rectangular patches are optimized to achieve the required phase shift for each beam at central and extreme frequencies in the working band. The reflectarray has been designed to produce a contoured beam for a European coverage in H-polarization in a 10% bandwidth, and a pencil beam to illuminate the East Coast in North America in V-polarization. The measured radiation patterns show that gain requirements are practically fulfilled in a 10% bandwidth for both coverages, and the electrical performances of the breadboard are close to those of a classical dual gridded reflector

Broadband Design of a Single Layer Large Reflectarray Using Multi Cross Loop Elements

A novel method is proposed to design a single layer large printed reflectarray with multi cross loop elements of variable loop length for broadband operation. Different classes of cross loop elements were used in the design and optimization of this reflectarray. The dimensions of these cross loops are adjusted using an optimization technique to achieve the required phase distribution in a given frequency band. A Ku-band square offset-fed reflectarray of 400 mm times 400 mm dimensions was designed and fabricated using this technique and both simulations and measurement results demonstrated improved gain bandwidth performance. A large Ku-band reflectarray of 800 mm times 800 mm dimensions was designed using the same technique, and the calculation results show a significant improvement in gain-bandwidth performance for the optimized reflectarray.

The Phoenix Cell: A New Reflectarray Cell With Large Bandwidth and Rebirth Capabilities

This letter presents a new phase-shifting cell for linearly polarized reflectarray applications. It provides a nearly 360° phase range and naturally comes back to its initial geometry after the phase cycle has been achieved. A complete analysis of the resonating mechanism is given, and a low dispersion (<;30°/GHz) is demonstrated over a large bandwidth (18%) in simulation.

A steerable reflectarray antenna with MEMS controls

A reflectarray antenna in Ka-band is currently developed under the French research project ARRESAT. Reflectarrays become attractive for satellite telecommunications, as long as they exhibit low losses. Due to the emergence of the MEMS technology, such features may be obtained. This communication presents a potential application mission, and the development of low losses phase shift elements, using MEMS switches. The technological and electrical considerations that govern the accommodations of these switches within the reflectarray are detailed. Measurements of the active phase shift elements are shown.

Compact Ka-Band Lens Antennas for LEO Satellites

Two new compact lens antenna configurations are presented and compared for data link communications with LEO satellites at 26 GHz. These lenses match a secant type radiation pattern template in the elevation plane while having a mechanically scanned sector beam in azimuth to enhance gain as much as possible. No rotary joints or multiple feeds are required and emphasis is put also on the compactness of the proposed solutions (< 6lambda0). Two alternative lens configurations are evaluated numerically and experimentally: one is based on modified axial-symmetric dome lens geometry, and the other one consists of a full 3-D double-shell lens antenna. In contrast to current nearly omnidirectional antennas, the directivity of our lens prototypes is above 15.4 dBi. Up to 4.2 dB loss obtained in the prototypes can be significantly reduced by using lower loss dielectrics and matching layers, without affecting the conclusions. The numerical and experimental results are in good agreement with the radiation specifications given the compact size of the antennas.

Scale-Changing Technique for the Electromagnetic Modeling of MEMS-Controlled Planar Phase Shifters

A scale changing approach is proposed for the electromagnetic modeling of phase-shifter elements used in reconfigurable microelectromechanical system (MEMS)-controlled reflectarrays. Based on the partition of the discontinuity plane in planar sub-domains with various scale levels, this technique allows the computation of the phase shift from the simple cascade of networks, each network describing the electromagnetic coupling between two scale levels. The high flexibility of the approach associated with the advantages of the integral equations formulations renders this original approach powerful and rapid. The scale-changing technique allows quasi-instantaneous computing of the 1024 phase shifts achieved by ten RF-MEMS switches distributed on the phase-shifter surface. Moreover, the proposed approach is much better than the finite-element-method-based software in time costing. Experimental data are given for validation purposes

Small-Size Shielded Metallic Stacked Fabry–Perot Cavity Antennas With Large Bandwidth for Space Applications

New configurations of small-size shielded metallic Fabry-Perot (FP) antennas with improved performance over a large frequency band are presented in S-band for space missions. The bandwidth enlargement is obtained by stacking two FP cavities of different size, each of them presenting a low quality factor. Their radiating apertures measure around λ0 and 2 × λ0, respectively. Concentric corrugations are also introduced between both cavities to control the higher-order modes that are excited systematically in shielded small-size FP antennas due to lateral resonances. The obtained results are compared to those of a single-stage FP cavity antenna with the same aperture size. Several prototypes have been fabricated and measured. An aperture efficiency higher than 70%, a reflection coefficient smaller than -15 dB, and sidelobe levels lower than -20 dB have been obtained experimentally, over a wide frequency band (2.4-2.66 GHz). These characteristics make stacked FP cavity antennas very attractive to replace global coverage horn antennas, or to be used in feed clusters of multiple-beam antennas, especially in C- and S-bands, where they lead to more compact and less bulky solutions compared to classical feed horns.

Self-Generation of Circular Polarization Using Compact Fabry–Perot Cavity Antennas

A new configuration of a compact self-polarizing Fabry-Perot (FP) cavity antenna is presented. It is excited in single-linear polarization at 45° and radiates in circular polarization. It consists of a polarizing FSS (used to ensure the polarization conversion) and a corrugated ground plane (designed to guarantee the resonance conditions for both incident orthogonal linear polarizations). A compact shielded FP antenna with an aperture of 1.62 λ0 is optimized and fabricated in S -band to validate the concept at 2.5 GHz. A 3-dB axial-ratio bandwidth of about 1.9% is achieved with an antenna height of only 0.8 λ0. The experimental results are in good agreement with the simulations. This antenna configuration is attractive for narrowband applications, like the space ones in C- or S-bands.

Self-Polarizing Fabry–Perot Antennas Based on Polarization Twisting Element

A new configuration of a self-polarizing Fabry-Perot (FP) antenna is presented to generate circular polarization with high gain levels using a simple linearly polarized feed. It consists of an FP resonator combined with a polarization-twisting ground plane. An analytical model is proposed to facilitate the antenna design, and the corresponding results are shown to be in very close agreement with full-wave simulations. The experimental prototype built in -band exhibits a combined bandwidth (3 dB axial ratio, 3 dB gain drop, and 10 dB impedance matching) of 3% with a maximum realized gain of 18.0 dB. The antenna is completely shielded with an aperture size of and a height of only . Such antennas are attractive candidates for high-power space applications at low frequencies ( -to -bands) where standard horns are very bulky.