A switched-beam antenna utilizing a radial guide with coaxial probes and a dielectric transition to free space

Research on smart antenna systems, involving switched-beam and phased array configurations, has attracted much attention in recent years. One variety of such an antenna is a circular array consisting of a single active monopole surrounded by a concentric array of passive monopoles terminated in reactive loads, which are positioned on a finite circular ground plane (Yang, K. and Ohira, T., 200 1; Lu, J. et al., 2001). Our previous paper on this type of array (Bialkowski, M.E. et al., Proc. 2002 IEEE-Antennas and Propag. Soc. Int. Symp., vol.2, p.268-71, 2002) concerned the use of short and open circuit loads to steer its beam in azimuth. Both ordinary and top-hat monopoles have been investigated for use in this array. In order to have more degrees of freedom for achieving the required return loss bandwidth and shaping the beam in elevation, we introduce a modification to this array. It concerns housing the array in a radial guide and including a radial-to-free space transition in the form of dielectric taper. The operation of the free space circular array monopole antenna is discussed. This is then followed by an investigation into the effect of adding an upper ground plane and the transition to free space. Results from the simulations of this type of antenna are shown.