Hindawi Publishing Corporation International Journal of Microwave Science and Technology Volume 2008, Article ID 784526, 7 pages doi:10.1155/2008/784526 Research Article A New Design of Compact 4 × 4 Butler Matrix for ISM Applications Mbarek Traii, 1 Mourad Nedil, 2 Ali Gharsallah, 1 and Tayeb A. Denidni 3 1 Laboratory of Electronic, Faculty of Sciences of Tunis, Tunis El Manar University, 2092 Tunis, Tunisia 2 Laboratoire de Recherche T´ el´ ebec en Communications Souterraines LRTCS 450, 3e Avenue, Local 103 Val-d’Or (Qu´ ebec), Canada J9P 1S2 3 INRS-EMT, Universit´ e de Qu´ ebec, Place Bonaventure 800, de la Gauchti` ere Ouest West, Suite 6900, Montr´ eal, QC, Canada H5A 1K6 Correspondence should be addressed to Mbarek Traii, traii moncef@yahoo.fr Received 5 May 2008; Revised 9 September 2008; Accepted 22 December 2008 Recommended by Kenjiro Nishikawa A novel design of a compact 4 × 4 Butler matrix is presented. All the design is based on the use of a Lange coupler with certain geometrical characteristics. This matrix occupies only 20% of the size of the conventional Butler matrix at the same frequency (80% of compactness). To examine the performance of the proposed matrix, the Lange coupler and the Butler matrix were simulated using Momentum (ADS) and IE3D softwares. Simulation results of magnitude and phase show a good performance. Furthermore, a four-antenna array was also designed at 2.45 GHz and then connected to the matrix to form a beamforming antenna system. As a result, four orthogonal beams at −45 ◦ , −15 ◦ , 15 ◦ , and 45 ◦ are produced. This matrix is suitable for wireless application at ISM band of 2.45 GHz. Copyright © 2008 Mbarek Traii et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction Smart antenna systems have been introduced to improve wireless performance and to increase system capacity by spatial filtering, which can separate spectrally and temporally overlapping signals from multiple users. Switched beam systems are referred as antenna-array systems that form multiple-fixed beams with enhanced sensitivity in a specific area. This antenna system detects signal strength, selects one of the several predetermined fixed beams, and switches from one beam to another as the user moves. One of the most widely known of switched beam networks is Butler matrix [1]. It is an N ×N passive feedingnetwork with beam steering capabilities for phased array antennas with N outputs and N inputs. Feeding an N-element antenna array using an N × N Butler matrix, N orthogonal beams can be generated, and each beam has a gain of the whole array. In most cases, circuits are designed using branch-line directional couplers [2]. However, in single-layer Butler matrix, hybrid coupler takes up over 50% of the area. It has a dimension of a quarter wavelength square and occupies a significant amount of the board area. For reducing the area, some techniques such as the use of lumped-element [3] have been proposed. However, lumped inductors and capacitors with the required values are not always available and their tolerance is quite larger. Thus, the need for compact circuits with simple structure and low cost is more and more attractive. The problem of miniaturization was reported in [4], where semilumped branch-line couplers have been pro- posed. The broadband 3 dB coupled line directional couplers were used in [5]. In this case, a small size has been achieved but the bandwidth of the Butler matrix is limited by differential phase characteristics. In [6], the authors have proposed a stripline Butler with broadband differential phase matrix. However, the stripline technique presents high manufacturing costs and complexity [7]. The most attractive technique for designing and manufacturing microwave cir- cuits is a microstrip technique since it uses a single laminate layer and allows easy mounting of surface mount devices and components.