Nelson J. G. Fonseca

Design and Implementation of a Planar 4x4 Butler Matrix in SIW Technology for Wide Band High Power Applications

This paper introduces a novel design of Butler matrix in substrate integrated waveguide (SIW) technology with wide frequency band characteristics. Butler matrices are particularly useful in advanced antenna design and characteristics such as wideband operation, power handling, manufacturing, integration, cost, etc. are typical issues to be addressed in many applications. The proposed planar 4 £ 4 Butler matrix provides an interesting solution to most of these issues. Wideband operation is achieved thanks to improved cross-couplers. These components are also characterized by higher power handling when compared to E-plane couplers. The use of SIW technology enables to reduce insertion losses compared to other printed technologies, while maintaining most advantages of such technologies such as high integration, manufacturing simplicity, low weight, etc. The proposed design is fully described, from the elementary building blocks to the full assembly performances. The design is optimized for operation in Ku-band with a center frequency at 12.5GHz. A prototype of the 4 £ 4 Butler matrix is manufactured, and good performances are conflrmed over 24% relative frequency bandwidth. Potential use of this sub-system in multibeam antenna design is also discussed.

Circular Polarization Wide-Angle Beam Steering at Ka-Band by In-Plane Translation of a Plate Lens Antenna

A simple mechanical beam steering antenna concept is proposed for ground mobile terminals of Ka-band satellite and high altitude platform (HAP) providing broadband access services. The wide-angle elevation beam steering is achieved by in-plane translation of a thin offset flat lens in front of a stationary primary feed while full azimuth coverage is obtained by simple 360° rotation of the lens. A new strategy is also proposed to reduce the effective F/D of the focusing system and consequently the total antenna height without increasing beam distortion: a second small flat lens is added on top of the primary feed to create a virtual focus located well below the feed phase center. The challenge is to conciliate high gain both with wide beam scanning and reduced antenna height. Design rules are presented for this antenna concept along with a 27.3-dBi gain fabricated example for the up-link Ka-band (29.5-30 GHz), with circular polarization, 0° to 50° elevation scan, better than 2.8-dB scan loss and an effective F/D of only 0.55. Both lenses are 3.35-mm thick, formed by a suitable assembly of phase shifting unit cells with less than 0.4 dB of transmission loss in simulation. The main lens dimensions are 195 mm × 145 mm and its weight is 215 g. Total antenna height, including the feed is 84 mm.

C-Band Multiple Beam Antennas for Communication Satellites

Nowadays, broadband satellites operating at Ka-band and providing high capacity (above 100 Mbps) are mostly based on single-feed-per-beam (SFB) antenna configurations. This antenna farm, using typically three or four reflectors to produce the full dual-band (Tx/Rx) multiple beam coverage, provides high performance but leaves no or little room on the spacecraft for other missions. Accommodation constraints and the desire of operators to maximize and diversify their revenues per satellite have led to several studies on innovative antenna solutions enabling to reduce the number of reflector apertures. Multiple-feed-per-beam (MFB) antenna configurations, using only two apertures, are currently under development for broadband missions at Ka-band. C-band is a more mature business and operators are contemplating the possibility to apply the benefits of multiple beam antennas (MBA) to this frequency band. Due to the lower operating frequency, accommodation constraints are even more stringent and although still scarcely discussed, MFB antenna configurations at C-band are clearly of interest. This paper presents investigations on this topic. In particular, it is found that the MFB architecture applied in C-band is a more realistic approach when compared to the SFB option. Beam Forming Networks (BFNs) with periodic structure is the key to get compact feed clusters that can be allocated in large and medium-size platforms. A new four color scheme compatible with a very compact MFB feed array architecture is introduced.

Compact printed quadrifilar helix antennas for stratospheric balloons telemetry

Two pre-fractal printed quadrifilar helices antennas have been presented. These compact antennas offer good compromises between size and performances. The designs introduced in this paper reveal the feasibility of an axial length reduction between 30 to 40% without significant cross-polarization degradation. Experimental validations were presented at the conference.

High-Performance Electrically Thin Dual-Band Polarizing Reflective Surface for Broadband Satellite Applications

This paper describes an anisotropic impedance surface that provides dual-band linear-to-circular polarization conversion in reflection with the peculiar property that a same linear polarization is converted into a given circular polarization handedness over the first frequency band and into the orthogonal one over the second frequency band. This property is of interest for multiple beam satellite communication systems, as the transmit and receive signals are commonly operating in orthogonal polarizations. This paper demonstrates that a simple, electrically thin polarizer design can provide high-performance conversion over the extended frequency bands used for broadband satellite applications. Some insight on the operation of the proposed polarizer is provided, supported by equivalent circuit models and analytical formulas, and compared with full-wave simulation results. The proposed design achieves an axial ratio better than 0.2 dB in simulation at normal incidence. A further iteration of the design and breadboard, taking into account measurement and practical implementation errors, provides an axial ratio better than 0.5 dB in measurement over the full transmit and receive frequency bands allocated to broadband satellite applications within the K/Ka bands.

Multi-scale approach for the electromagnetic modeling of metallic FSS grids of finite thickness with non-uniform cells

In this communication, the Scale Changing Technique is used for the global electromagnetic simulation of frequency selective surfaces consisting of non-uniform rectangular waveguides perforating a thick metallic plate. Excellent agreement between the Scale Changing Technique and the Finite Element Method is observed with substantial reduction in computation time and memory when using the proposed technique, which may be compatible with an optimization process.

Architecture and implementation of planar 4 × 4 Ku-Band Nolen Matrix using SIW technology

A new Nolen matrix architecture based on SIW technology has been proposed and presented for the first time. The matrix has been optimized by using the commercial software HFSS to operate from 12.25GHz to 12.75GHz. The fabricated prototype has performances in good agreement with simulation results. The measured power-split imbalance stays within 1 dB over the specified bandwidth. The proposed design technique has the advantages of low cost, light weight and ease of fabrication. This planar realization is of great interest for integration in more complex microwave systems such as multiple beam antennas.

Miniaturized Array Antenna Using Artificial Magnetic Materials for Satellite-Based AIS System

The ground-based automatic identification system (AIS) is a coastal tracking and messaging system used by vessels for maritime traffic monitoring. The European SAT-AIS initiative aims at providing a space-based complementary system to extend the range of the existing AIS to high seas via very high frequency (VHF) satellite constellation. The AIS Miniaturized Antenna (AISMAN) activity concentrates on the development of a VHF array antenna for minisatellite platforms in low Earth orbit. Array element volume minimization and mass reduction are considered performance drivers due to the in-orbit array deployment and satellite mass requirements. Artificial magnetic materials (AMMs) have been chosen as design concept of the baseline array element due to the significant size reduction they can offer. Further technical solutions, such as slotted ground plane, combined with AMM, have allowed for an outstanding profile reduction, while preserving high radiation efficiency and low back radiation. Innovative testing methodologies have been specifically developed to handle truncation errors and echo signals while performing radiation pattern measurement of the array on a full-scale mockup platform in a hemispherical automotive near field (NF) range. This paper discusses the design of array elements, from breadboard to engineering model (TRL4), manufacturing and validation campaigns at single element and array level.

L-band compact printed quadrifilar helix antenna with ‘Iso-Flux’ radiating pattern for stratospheric balloons telemetry

Two sinusoidal profile compact printed quadrifilar helix antennas have been presented. Particular care has been given to the co and cross-polarization patterns during the parametric design process to produce antennas with performances very similar to the conventional one in those aspects. A size reduction ranging from 30 to 40% is confirmed. Experimental validation will be presented at the conference.

Optimization Procedure for Planar Leaky-Wave Antennas With Flat-Topped Radiation Patterns

We describe here an optimization procedure to shape the radiation pattern of planar two-dimensional (2-D) leaky-wave antennas. The structures under investigation are superstrate configurations made by partially reflecting screens (impedances sheets) over a ground plane and excited by open-ended waveguides. The antenna configuration providing the required radiation pattern is obtained by resorting to an ad hoc optimization procedure that minimizes the mean squared error between the target pattern and the actual radiated far field. The radiated field is analytically evaluated using a Greens function spectral approach to speed up the optimization process. Several kinds of radiation patterns can be obtained using the proposed algorithm. In this work, we focus our attention on flat-topped radiation patterns, suitable as element pattern for phased array antennas covering a limited angular field of view such as those considered for space applications. The proposed procedure is validated by full-wave results and measurements.