Analysis of Frequency-Selective Impedance Loading of Transmission Lines for Dual-Band Couplers

This article proposes an analytical design methodology for dual-band hybrid couplers and baluns structures for any arbitrary frequency ratio using a stub-loaded transmission line. An analysis of changing the impedance behavior of the stub, is carried out for the two bands of operation, which along with a dispersive analysis, emphasizes certain conditions where the existing methodology is not applicable. In addition, an extra degree of freedom has been included to increase the solutions for a given frequency ratio, thus providing greater flexibility and feasibility of the proposed structure. The design methodology is experimentally validated with the design and fabrication of dual-band branch-line and rat-race couplers for various commercial frequency bands. (C) 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE 21:325-335, 2011.