Ayman  N. Salman Younis, 
    Design and Simulation 4x4 Butler Matrix Array for ISM-Band,
    Journal of Mobile Communication,
    Volume 6,Issue 2,
    2012,
    Pages 22-27,
    ISSN 1990-794x,
    jmcomm.2012.22.27,
    (https://makhillpublications.co/view-article.php?doi=jmcomm.2012.22.27)
    Abstract: This study proposes an 4x4 planar microstrip array antenna with Butler matrix performing network can be used for a switched beam smart antenna system. The prototype antenna is operating in the ISM from 2.4-2.48 GHz for WLAN applications. The antenna is built on a FR4 substrate with relative permittivity of &#949;<SUB>r</SUB> = 4.4, loss tangent of 0.02 and thickness of h = 1.6 mm. The performance of this smart antenna system was optimized and simulated by using commercially available full-wave, Method of Moment (MOM) based electromagnetic simulator Zeland IE3D.
    Keywords: microstrip;Butler matrix;Switch beam smart antenna system;electromagnatic;substrate;tangent