732 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 47, NO. 6, JUNE 1999 Performance of Lens Antennas in Wireless Indoor Millimeter-Wave Applications Carlos A. Fernandes, Member, IEEE, and Jos´ e G. Fernandes, Member, IEEE Abstract—Dielectric lens antennas can be designed to produce highly shaped beams that signiﬁcantly improve the system per- formance in emerging wireless indoor millimeter-wave systems. A lens conﬁguration is analyzed in this paper that produces a circularly symmetric cell with uniform spatial power distribu- tion, fairly sharp boundaries, and scalable cell radius. The last characteristic is used to control the reﬂections at sidewalls. A hemispherical coverage lens antenna is designed for the mobile terminal (MT) to ensure relatively free movement. The impact of these antennas is analyzed in terms of cell coverage and channel time dispersion, considering the effect of cell radius scaling, and MT antenna tilting. Measurements and simulations show that the proposed lens antennas outperform common solutions based on pyramidal horns or biconics. Index Terms—Lens antennas, millimeter-waves, shaped beams, wireless applications. I. INTRODUCTION T HE wide acceptance of mobile services by the users and strong competition in the ﬁeld has led to an explosive growth in cellular and mobile telephony in the last ten years. The increasing need for larger bandwidths to support broad- band services has been a major driving force pushing the development of mobile/wireless broad-band systems, aiming to extend to the mobile users the wide range of services available in the broad-band integrated services digital network (B-ISDN). Due to the saturation of the lower part of the frequency spectrum, this type of system will operate in the millimeter-wave band. It has been shown that, at these frequencies, the antennas have a signiﬁcant impact on the characteristics of the multipath radio channel and, therefore, they play a key role in system performance [1]–[3]. The power available from solid-state devices is limited and, thus, it should be uniformly distributed over the cell while keeping the channel time dispersion at low values since it directly impacts on the achievable carrier bit rate (CBR). Adaptive equalization is unavoidable in high bit- rate systems, but it cannot cope with large time dispersion values often encountered in typical scenarios. Hence, some directivity is required both at the base and mobile station Manuscript received December 1, 1998; revised February 4, 1999. This work was supported in part by the Funda¸ c˜ ao para a Ciˆ encia e a Technologia under Project PBIC/C/TIT/2501/95. C. A. Fernandes is with the Instituto de Telecomunica¸ c˜ oes-P´ olo Lisboa, 1049-001 Lisbon, Portugal, and is also with the Instituto Superior T´ ecnico, 1049-001 Lisbon, Portugal. J. G. Fernandes is with the Instituto de Telecomunica¸ coes-P´ olo Aveiro, 3810 Aveiro, Portugal, andis also with Universidade de Aveiro, 3810 Aveiro, Portugal. Publisher Item Identiﬁer S 0018-9480(99)04280-5. antennas to favor the link budget and to cooperate with the equalizer in the mitigation of the channel time dispersion. However, the antenna directive requirements must not entail a restriction of terminal mobility. In this paper, we analyze the impact of using a novel and quite inexpensive antenna conﬁguration for indoor scenarios that is able to cope with the above requirements. The basic idea is to use a shaped dielectric lens antenna at the base station (BST) hanging from the ceiling, which produces a secant squared ( ) type of radiation pattern in the elevation plane in order to compensate for the free-space attenuation at each direction. The BST antenna is paired with an hemi- spherical pattern lens in the mobile terminal (MT) so that the average received power remains reasonably constant for all positions of the mobile or portable terminal within the cell. The radiation patterns of the BST and MT lens antennas are circular symmetric. The proposed lens combination further provides very sharp cell boundaries with negligible radiation outside the cell limits. A remarkable characteristic of patterns is that cell dimensions are scaled to the antenna height. This provides a simple means to control the illumination of the walls at the edges of the cell to maintain an adequate compromise between multipath effects and the need for alternative paths in case of line-of-sight (LOS) blockage. II. LENS ANTENNA The general design principles for axisymmetric amplitude- shaping dielectric lenses are addressed in [4]. In the present case, the lens is fed by the aperture of a circular metallic waveguide, which is embedded in the lens body. The lens surface is conveniently shaped to transform the feed aperture radiation pattern into the desired output beam. This antenna conﬁguration is quite ﬂexible, allowing the design for different target patterns from secant squared to hemispherical type, with linear or circular polarization. The lens antenna design involves a two-step procedure based on geometrical and physical optics. Speciﬁc software tools were developed, which allow a reliable calculation of the lens proﬁle and prediction of the corresponding radiation characteristics. Plexiglas material ( ) was used in all prototypes described throughout, although other very low-loss commercially available materials ( ) with the same permittivity were tested for these type of lenses, giving similar radiation patterns, but higher gain. For linear polarization, the BST lens is excited by the mode of the circular waveguide, producing a circular 0018–9480/99$10.00  1999 IEEE