International Journal of Electrical and Computer Engineering (IJECE) Vol. 7, No. 2, April 2017, pp. 888~893 ISSN: 2088-8708, DOI: 10.11591/ijece.v7i2.pp888-893  888 Journal homepage: http://iaesjournal.com/online/index.php/IJECE Wideband Branch Line Coupler with Open Circuit Coupled Lines Muataz Watheq Sabri, N A Murad, M K A Rahim Department of Communication Engineering, University Technology Malaysia, Malaysia Article Info ABSTRACT Article history: Received Dec 13, 2016 Revised Mar 15, 2017 Accepted Mar 30, 2017 This paper focuses on the design of a Wideband Branch Line Coupler by using open circuits coupled lines technique. The design is implemented by adding four open circuits coupled lines to the structure of the Conventional Branch Line Coupler. The proposed design of Wideband Branch Line C                 3 z     -3         orts. The prototype is fabricated and measured to validate the simulated results. A similar Wide Bandwidth is observed on simulation and measurement. The structure achieved a fractional bandwidth of 42.63%, and return loss of 21 dB compared to the Conventional Branch Line Coupler (BLC). Keyword: Branch line coupler Coupled lines Fractional bandwidth Microstrip Wideband Copyright © 2017 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Noor A. Murad, Department of Communication Engineering, University Technology Malaysia, Balai Cerap UTM, Lengkok Suria, 81310 Skudai, Johor, Malaysia. Email: asniza@fke.utm.my 1. INTRODUCTION A Hybrid 3 dB Branch Line Couplers delivering an equal power division and quadrature phase difference are one of the fundamental circuit components for array antenna, power amplifiers, filters, and modulators. However, a narrow bandwidth noticed as a major limitation in the conventional branch line coupler design, where the design method based on transmission line lengths result in a narrow band characteristic of the coupler. A wideband branch line coupler has been recently adopted in microwave devices and applications such as 4G cellular system, Wi-Max systems, and antenna beamforming systems, as an advantages of wider bandwidth provides a more capacity and more date rates, while one of the major limitation beside the Wider bandwidth is the size of the Wideband BLC coupler to be implemented in the RF system devices at low frequency. To overcome this limit a simple technique flowing more sections had been suggested [1]. Additionally, in the last 60 years the researcher were focusing on significant principle based on matching condition between each port [2]. Where various researches [3-9], increased the bandwidth by using this important principle of matching condition. To achieve a good matching condition for wider bandwidth and uniform power distribution characteristics, the equivalent impedance and the flat coupling characteristics of conventional line coupler have been investigated [2], [3]. After these analyses, various single section broadband branch line couplers have been developed by using various matching techniques, such as using a double quarter-wave transformer [4] in 1987, a serial branch and open circuited stub of [5] in 1990, open and short circuited stubs [6] in 2006, tuning stubs [7] in 2008, series open-circuited stubs [8] in 2010, and coupled lines in this work. Another new method such as bond wire was presented [9]. The open circuited coupled lines implemented in this work provide a wideband matching condition [10], inherent DC blocking for various networks of active devices, for various antenna arrays, and for various filters.