Effects of ground plane truncations on the array behaviour of a smart antenna terminal with modular architecture

Modern communication systems should provide high data rates to enable e.g. user access to multimedia services. A Smart Antenna Terminal (SANTANA) with digital-beamforming technology is developed for these applications. The array geometry is based on a modular concept, i.e. the array is set up by 4 x 4 single microstrip-element modules. This enables the replacement of defective elements and also makes it easy to increase the directivity of the array by adding further modules. The gaps caused by the modular architecture and therefore the truncated groundplanes of the modules may influence the array behaviour. The modified array behaviour due to these gaps can be regarded as the superposition of the changed radiation patterns of the single elements. This paper describes the research on the influence of the array gaps on the single-element behaviour with respect to input impedance and far-field patterns. All possible gap positions are examined and simulations are presented, i.e. the application of the principle of sequential rotation in the array to achieve circular polarization with linear polarized single elements is taken into account. Furthermore the influence on 2 x 2 element subarrays is studied. Finally the simulation results are compared to measurements.