ITEE Innovation Expo 2008 : Project Details

Components for Wideband Microwave Sub-systems: Hybrids and Transitions

Abstract Microwave directional couplers play an important role in passive microwave circuit. They are used to combine or divide RF signals with appropriate phase of 90degree. The couplers are found mainly in microwave sub-system such as balanced mixers, modulators and multi-port amplifiers. Meanwhile, couplers are also considered to be used as a significant component of wideband microwaves six-port reflectometer which is an alternative to the conventional Vector Network Analyzer (VNA). The thesis reviews a variety of ideas and existing technologies to design a 3dB quadrature coupler. Even and odd mode analysis as well as microstrip-slot coupling method are studied and applied. Then, a new wideband (3-11GHz) multilayer directional coupler using a non-uniform broadside slot-coupled CPW is introduced and investigated. The approach is using two microstrip lines separated by a non-uniform slot in the common ground plane. The lines and slot contain three rectangular shape sections and each section realizes different coupling factor for obtaining overall 3dB coupling of design requirement. The coupler is designed using Rogers RO4003C substrate with thickness of 0.508mm, loss tangent of 0.0027 and the dielectric constant of 3.38. Some modified designs are also investigated such as adding non-uniform capacitive plates or conducting disks with different sizes to initial design for improving the return loss, coupling, isolation and phase difference of original coupler. The design is accomplished with the commercially available design tool CST Microwave Studio. The results obtained from the design are assessed in terms of return loss, through, coupling and isolation.