This paper discusses the architecture of an adaptive transmitting microstrip array that allows highly flexible beamsteering and beamshaping. The antenna array is digitally controlled by a field programmable gate array (FPGA) board. The power and phase of the excitation signals delivered to the array elements are optimized using an algorithm based on particle swarm optimization (PSO), which includes all electromagnetic effects such as mutual coupling and installed performance. Further, the efficiency of the proposed approach is validated by synthesizing various beam patterns, including side lobe level control and beam shaping for cosecant squared and isoflux contours. Very good agreement between simulated and measured results is thereby observed. The paper also addresses implementation aspects that are not reported in detail in literature, such as the compensation for the faulty antennas or transmitting channels, as well as the calibration procedure applied for the experimental validation of the proposed architecture.INDEX TERMS Active element pattern, beamforming, mutual coupling, optimization methods, particle swarm optimization, antenna measurement.

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Abstract-This paper describes the concept and the development of key components of a novel multiple-beam antenna for satellite applications. The antenna is designed to be used in a transparent high-rate data relay system that links several low earth orbit (LEO) satellites to a single ground station via a satellite positioned on a geostationary orbit (GEO). The proposed antenna is based on the concept of an array-fed reflector. The antenna can track LEO satellites by switching between different subarrays of a bigger multifeed array using a reconfigurable switch matrix based on radio frequency micro-electromechanical system (RF MEMS) switches. The radiation characteristic of the antenna is further improved by combining digital beamforming with beam switching. In order to validate the proposed antenna concept and to show its suitability for space applications a demonstrator has been built. Measurements of the antenna's key components and of the demonstration system are given.

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