Wong Fai Leung (postgraduate student at the Microwave & Wireless Communication Laboratory) was awarded 1st Runner-Up in the Advance Program of the 5th IEEE (HK/Macau) AP/MTT Postgraduate Conference held at the University of Macau.

Paper Title: Novel Branch-Line Coupler Designs for Dual Band Applications

Author: F. L. Wong and K. K. Cheng

Abstract:
Branch-line coupler is a popular passive device for microwave and millimeter-wave applications. The standard design of branch line coupler offers specific power dividing ratio and phase relationship between the output ports over the operating bandwidth. Branch line coupler is commonly used as building blocks for balanced amplifier and mixers.

However, the conventional design of branch line coupler is basically consisted of quarter wavelength transmission lines which lead to inherent narrow band operation and as a result, its application to wide-band and multi-band system is thus greatly limited. In the past years, various reports concerning bandwidth enhancement and size reduction techniques have been published in the literature. Recently, dual band branch line coupler implemented using lumped elements was also reported.

In this paper, two novel planar 90?3-dB branch line coupler designs are presented. Both designs offer dual-band operation, low insertion loss and compact size. Basic operating principles of both configurations, practical implementation issues such as branch-line impedance realization are addressed. Finally, for experimental verification, both the simulated and measured results of 900/1800 MHz branch-line couplers constructed by microstrip technology are demonstrated.