Design of Controlled RF Switch for Beam Steering Antenna Array

Abstract

A printed dipole antenna integrated with a duplex RF switch used for mobile base station antenna beam steering is presented. A coplanar waveguide to coplanar strip transition was adopted to feed the printed dipole. A novel RF switch circuit, used to control the RF signal fed to the dipole antenna and placed directly before the dipole, was proposed. Simulated and measured data for the CWP-to-CPS balun as well as the measured performance of the RF switch are shown. It has demonstrated the switch capability to control the beam in the design of beam steering antenna array for mobile base station applications. The use of adaptive array antennas for cellular base station application has recently become an active area of research and development (1{3). Base station antennas normally radiate omni- directionally or in broad sectors, in which the most of the power is radiated in other directions than toward the user. This causes waste of power and interference for other users. Therefore new versions of base station antennas are now being made to overcome the problem by using antennas that have narrow steerable beams. These can give large increment in capacity, and the possibility of tracking mobile phones or vehicles. In authors' previous work (4), a set of simple design procedures for beam steering single circular and concentric circular ring antenna arrays was proposed and analyzed theoretically (see Fig. 1). In the paper, the design theory was formulated and the results of the proposed analytical model, validated by a numerical model, were presented. Beam steering was achieved by implementing an ON/OFF system concept to excite only speciflc elements of the array dipole antenna. In this study, a following-up study was carried out on designing and implementing the RF switch for practically realising the beam steering using the proposed ON/OFF antenna array system. A novel design principle of RF switch, used to control the RF signal fed to each of the antenna elements in an array, was proposed. Moreover, a coplanar waveguide (CPW) to coplanar strip (CPS) transition was employed to feed the antenna element (i.e., printed dipole). Subsequently, performance of the CPW-to-CPS fed dipole antenna controlled by a RF switching circuit for duplex operation was evaluated and verifled through hardware realisation. The measured results for the CPW-to-CPS balun and practical performance of the RF switch are shown in this paper.