ORIGINAL PAPER George S. Miaris Æ Eleftheria Siachalou Theodoros Samaras Æ Sotirios K. Goudos Elias Vafiadis Æ Stavros Panas On the base stations antenna system design for mobile communications Received: 9 February 2004 / Accepted: 17 August 2004 / Published online: 12 January 2005 Ó Springer-Verlag 2005 Abstract The design of a base station antenna for mobile communications is presented. The orthogonal method (OM) is applied under constraints on nulls of the radi- ation pattern. In the synthesis process the mutual cou- pling between the elements of the antenna array could be taken into account. Beam tilting and direction of arrival are also considered. The whole design is completed by implementing a special architecture of the antenna. Fi- nally, some examples show the applicability of our technique. Keywords Mobile communications Æ Base station antennas Æ Beam tilting Æ Beam forming Æ Orthogonal method 1 Introduction The increasing demand for wireless services has led to the expansion of antenna technology. Most of the existing studies have to do with simulation tools of cel- lular networks [1], and with combination of numerical methods that model coupling and far-field propagation effects [2, 3]. Smart antenna arrays mounted on base stations (BS) increase the network capacity and the error probability performance by using the space-division multiple access (SDMA) schemes. The antenna array is directed toward the desired user by combining the direction of arrival (DoA) process and the beam forming process [4–6]. Several works are in progress and a num- ber of illustrative papers have described the technology and methods in the area of smart antennas [7, 8]. The main purpose of smart antennas is to produce a specific radiation pattern at the specific time interval. The instantaneously required radiation pattern is defined by the positions of the mobile unit (MU) and the interfering sources. The desired radiation pattern should present a maximum (or direct the main beam) toward the position of the targeted user, while at the same time it should present ‘nulls’ in the directions of the other users and the interferers. In the present paper a study on the design of a base station antenna for mobile communications is given. The importance of beam tilting of the antenna is examined, considering the maximum achievable bit rate due to intersymbol interference (ISI). In the antenna design the orthogonal method (OM) is applied where the coupling between the elements could be taken into ac- count. The adaptive architecture in conjunction with the DoA is described. Also the appropriate weights of the antenna elements and the necessary I/Q modulators are addressed. Finally, examples are given to show the applicability of the whole design and operation proce- dure. 2 Beam tilting The data transmission rate through mobile mutipath fading channels is limited because of the resulting ISI, which makes the transmitted pulses no longer distin- guishable at the receiver. In the literature [9], one can find studies where, for a given antenna pattern, the beam tilting increases the rate ability of the system. The re- ceiver’s sensitivity as well as the reflections and the dif- fusely scattered conditions play important roles in ISI. We begin our study by using a simple propagation model (see Fig. 1). A wave beam is transmitted from a BS to the MU over a distance r. If we suppose that the transmitted signal is reflected on a plane surface, the reflected wave will disperse its energy and part of it will G. S. Miaris Æ T. Samaras (&) S. K. Goudos Æ E. Vafiadis Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece E-mail: theosama@auth.gr E. Siachalou Æ S. Panas Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece Electrical Engineering (2006) 88: 157–163 DOI 10.1007/s00202-004-0267-x