Design of multi-port network utilizing microstrip-slot technique for ultra wideband system

Abstract

Nowadays, there is a lot of interest on the research and development related to ultrawideband system due to the increasing demands on the applications with low power, low cost and low interference. Thus, to cope with these demands, various researches are required for the development of front-end microwave components, which include six-port network as an alternative to a mixer-based design. The configuration of a six-port network is constructed by combining coupler and power divider. In the interest to have a simple design and convenient usage to form the sixport network with ultra wideband (UWB) operation, new power divider and coupler are designed by using microstrip-slot technique. All the proposed designs are simulated via the use of CST Microwave Studio 2010 and realized using Rogers TMM4 with a conductor coating of 35 μm, thickness of 0.508 mm and dielectric constant of 4.5. The developed prototypes of the proposed designs are verified by measurement using a vector network analyser (VNA). In this thesis, a design of twosection power divideris proposed with a great UWB performance of -3.8 dB ± 0.5 dB transmission coefficient and 0º ± 2º phase difference. This power divider has bandwidth improvement of 11.9% and size reduction of 23.33% compared to the conventional design. Meanwhile, for the coupler design, a UWB coupled-line coupler with zig-zag-shaped slot that has 3 dB ± 2 dB coupling coefficient and -90º ± 5º phase difference is proposed. The proposed coupler has 109.5% bandwidth improvement with the length reduction of 20% compared to the conventional coupler. The proposed UWB coupler is then implemented into a new proposed structure of UWB 90º power divider. Then, three configurations of six-port networks formed by UWB coupler, two-section power divider and 90º power divider are designed; which are named as Type I, Type II and Type III. From the observation, Type III demonstrates the best UWB performance with magnitude imbalance of ± 5 dB and phase imbalance of ± 10° that achieving the specified UWB design goal. Furthermore, Type III has the respective size reduction of 57.16% and 34.67% compared to Type I and II. In addition, by comparing to the previous works, the proposed design has broadest bandwidth of 100% and smallest size of 50.92 mm x 35 mm. Hence, the proposed six-port network has very well UWB performance with relatively compact size and simple design, which is easy to be fabricated.