Yann Cailloce

An Enhanced

This letter presents a first step toward the design of an enhanced multifeed EBG structure that serves as a focal-plane array for a Ka-band reflector for space applications in the 29.5-30-GHz band. The desired Earth coverage is the starting point for the antenna design. As shown in this letter, significant coupling can deteriorate the performance of the multifeed EBG antenna. In order to demonstrate this, the results are compared to those of the single-feed reflector antenna. Filters are then connected to the multifeed antenna ports to control the coupling in a constructive way and obtain good radiation characteristics. Finally, the global feed architecture (EBG structure + filters) is used to illuminate a reflector antenna in order to characterize the antenna performance (C/I ratio, EoC gain).

Ka

A new simplified methodology for the design of microwave cavity filters has been presented. The presented work is based on the optimization of Belevitch polynomials and inspired from the Simplified Real Frequency Technique (SRFT). One can bypass the use of computationally expensive circuit simulation softwares which are used to optimize the lumped element circuit model of the cavity filters. The procedure is applied for the design of filters for a multi-feed filter-antenna subsystem for space application.

-Band Reflector Focal-Plane Array Using a Multifeed EBG Structure

The demand for multimedia communications via satellite systems have increased considerably in the last years. Normally, the satellite coverage is composed of a hexagonal lattice of many small beams. An example of an experimental satellite coverage named “Agora” is composed of 40 0.65°-diameter spots, using 4 frequency channels in a 4x reuse scheme with the same circular polarization. A first solution which meets the requirements of such a mission (C/I, efficiency, roll-off) is the use of 4 Rx/Tx parabolic reflectors on the same satellite, providing each a family of spots at the same frequency. This solution has the drawback of heavy weight and the challenging accommodation of 4 reflectors on the platform. These 4 reflectors could be replaced by only one, when using a focal array which is capable of generating a specific illumination law (overlapped beams). This focal array could be composed of an active BFN which is, unfortunately, expensive and has moderate RF efficiency. Several studies have shown that overlapped beams could be obtained by using multi-feed EBG antennas [1, 2]. The major problem of these structures is the mutual coupling between different feeds. It was demonstrated recently that suitable filter designs could be connected to each feed [3, 4] in order to ensure the isolation between different channels and also to reconstruct properly the radiation patterns which are otherwise disturbed by the coupling. In [4] and [5] it is shown that the use of a matched multi-feed EBG antenna with 2 linear polarizations and 2 frequency channels provides a 4x reuse scheme that simplifies the system architecture. In fact, the use of a matched antenna relaxes the need for the filters to provide matching inside the operating band; they just need to act like a short circuit with the appropriate phase outside their operating band, in order to reconstruct properly the radiation patterns. On the other hand the use of 2 frequency channels reduces the number of required filters (2 filters instead of 4). Finally, linear polarizations are considered in order to prevent the design of bulky filters for circular polarization (6 poles filters with 6 cavities are needed to ensure the transmission of circularly polarized wave and isolation between channels). In this paper, a metallic multi-feed EBG antenna operating in Ka band [29.5–30] GHz is presented, and its performances before and after connecting the filters will be shown. Finally, this antenna is used to illuminate a reflector and the coverage characteristics (C/I) will be given.

A simplified methodology for matched filter design with constraints - filter-antenna subsystem for space application

INTRODUCTION Generally speaking, space has not been considered so far as a key player in new technologies. It is more a fast follower, the reason being the long and costly qualification programs which are directly linked to the combination of long life time (15 years for GEO satellites) and operation in harsh environment. Nevertheless the satellite industry could experience in the coming years, its biggest evolution since it joined the ranks of commerce. Thanks to increasing constraints on performance, cost and development cycles, it is possible that space industry could be at the cutting edge of the major technical evolution which is taking place in electronic industry. In some cases this evolution is going jointly with another low volume high added value industry : the military industry. In this paper, we will present and discuss Alcatel Space view in RF MEMS emerging technologies that may impact future telecom payload.