Broadband parallel-coupled quadrature coupler with floating-potential ground plane conductor

The design of a parallel-coupled directional coupler, which has a broadband performance, is presented. A floating-potential ground plane conductor is used underneath the coupled region to relax the requirement for a narrow slot between the coupled lines and to improve the isolation and return loss performance of the device. The simulated and measured results show that the designed coupler exhibits a coupling of 3 ± 1 dB across the band 4-10.2 GHz, when the spacing between the coupled lines is 0.13 mm, which is easy to manufacture. This broadband coupling is accompanied by an isolation and return loss which are better than 15 dB across the band 3.1-10.6 GHz. The simulated and measured results show good phase stability and flat group delay across the ultra wideband. The designed device has a compact size with a dimension of 30 mm × 20 mm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2304-2307, 2008; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.2370