Far Field Pattern Analysis and Measurement of a Digital Beam Forming 8??8 Antenna Array Transmitting from 29.5 to 30 GHz

The increasing demand for mobile access to fast data services is one of the drivers for future broadband satellite systems at Ka-Band. Antennas employing Digital Beam-Forming provide fast and flexible reconfiguration required in such systems without the necessity for moving mechanical parts. The antenna presented in this paper is a circularly polarised, 8times8 patch element array, consisting of four 4times4 array building blocks. The array is used for a digital beam forming terminal (transmit system) operating from 29.5 GHz to 30.0 GHz. The circular polarization of the patch elements is achieved using two decoupled feeds and one 90deg hybrid ring per element. In addition, the antenna elements are sequentially rotated to further enhance the polarisation behaviour of the array. At a time, 16 antenna elements, with hybrid ring feeds and own calibration network are integrated in one complex LTCC multilayer module. Such 4times4 building blocks can be calibrated automatically using an internal calibration receiver. This paper will focus on the far field analysis, the far field measurements, EIRP measurements and efficiency measurements of the calibrated 8times8 antenna array. First, the simulation and analysis of the array is described. In addition to far field pattern computation for different steering angles, possible retroaction of the beam steering on the reflection coefficient is analysed. In the following, the far field and EIRP measurements of the calibrated antenna array are illustrated. An estimation on the antenna efficiency is given. Different phase offsets and amplitude tapers are applied, to provide the steering of the main beam and make for sidelobe suppression.