Wideband branch-line couplers with arbitrary coupling levels are demonstrated. By integrating single-section quarter-wave transformers at each port, wideband characteristic with excellent coupling flatness is achieved. Also, a method is demonstrated that introduces intentional mismatch for a further enhancement in bandwidth. Superior structural and design simplicity outperform previous wideband couplers. Branch-line couplers at 3 GHz are demonstrated experimentally that maintain the coupling level within 0.5 dB from the specified 10 dB in as much as a 50.9% bandwidth, with minimum return loss and isolation of 16.3 and 18.7 dB, respectively.
Bibliographical noteFunding Information:
Manuscript received July 21, 2011; revised October 23, 2011; accepted November 12, 2011. Date of publication December 16, 2011; date of current version January 11, 2012. This work was supported by the Low Observable Technology Research Center of Agency for Defense Development and Defense Acquisition Program Administration of Korea, and by the KCC (Korea Communications Commission), Korea, under the CPRC(Communications Policy Research Center) program supervised by the KCA (Korea Communications Agency) (KCA-2011-0902-1).
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Electrical and Electronic Engineering