Beamforming Antenna Array Combining Pattern and Polarization Diversity for Cognitive Radio Applications

Abstract

This paper presents a novel beamforming antenna array that combines pattern and polarization diversity for indoor cognitive radio systems. This combination is set to meet two goals. In order to reduce interference between users in cognitive radio networks by using pattern diversity, and to mitigate multipath fading in indoor environments by employing polarization diversity, so as to enhance the capacity and the reliability of communication link. The proposed structure is simulated, optimized, and its performance is verified by experiments. Measured results show that the proposed structure achieves an impedance bandwidth from 2.2 to 3.2 GHz, which covers the IEEE 802.11 b/g/n and WiMAX bands. By switching the input port, the antenna system can produce four beams at $$\pm 15^\circ$$±15ź and $$\pm 45^\circ$$±45ź that have circular polarization diversity; two of them have left-hand circular polarization and the other two beams have right-hand circular polarization. Moreover, radiation patterns with low cross-polarization level, good axial ratio around the center frequency, and low envelope correlation coefficient across the operating band are obtained. The measured gain at 2.4 and 2.6 GHz are 5.3 and 6.6 dBi, respectively. All these proprieties make the proposed antenna system very suitable for future cognitive radio applications, particularly in dense urban and indoor environments, where the challenge of interference and multipath fading are a major concern.