Progress In Electromagnetics Research Letters, Vol. 42, 109–118, 2013 A NOVEL DECOUPLING NETWORK USING PARALLEL COUPLED LINES FOR INCREASING THE PORT ISOLA- TION OF TWO COUPLED ANTENNAS Hui Wang 1, 2, * , Bin-Kai Ou 2 , Kam-Weng Tam 2 , and Wen Wu 1 1 Ministerial Key Laboratory of JGMT, Nanjing University of Science and Technology, Nanjing, China 2 Faculty of Science and Technology, University of Macau, Taipa, Macao, China Abstract—A compact decoupling network for enhancing the ports isolation of two coupled antennas is proposed in this letter. Parallel coupled lines (PCLs) and transmission lines (TLs) with different electrical lengths are considered to control the magnitude and phase of this decoupling network, respectively. The coupling coefficient of the PCLs is adjusted with various line widths and coupled gaps so that the magnitude of this network will be equal to that of the coupled antennas. And the electrical length of the series TLs can be controlled to make the signals of coupled antennas and decoupling network out of phase. Thus, the mutual coupling between the coupled antennas can be canceled. A prototype is fabricated on a RO4003 print circuit board (PCB) for demonstration. The measured results agree quiet well with the simulation ones. High antenna isolation and good matching are simultaneously achieved at the center frequency, i.e., 925MHz for global system mobile communications (GSM) which shows the compact decoupling network is suitable for reducing the isolation of size limited multi-antenna systems. 1. INTRODUCTION Adaptive beamforming exploits the degrees of freedom available in multiple-antenna systems to adapt to the mobile communications environment and to improve the quality and availability of the transmission link. At the same time, traditional smart antenna systems Received 15 July 2013, Accepted 28 August 2013, Scheduled 3 September 2013 * Corresponding author: Hui Wang (w h5300@sina.com).