Thin-film barium strontium titanate varactor tunable dual-band quadrature hybrid coupler

A thin-film barium-strontium-titanate (BST) and a conventional silicon varactor tunable dual-band quadrature hybrid couplers are characterized and compared in this article. Both structures are composed of four quarter-wavelength sections at a frequency located between the two operating frequencies, and with two pairs of open-ended stubs. Frequencies tuning make used of BST interdigital and silicon varactor diode capacitors connected at the open-ended stubs. The characterized BST interdigital capacitor presents a capacitive-tunability of 52% through an applied voltage of 0 to 25 V, while 82.5% is for the selected commercial silicon varactor diode. The silicon varactor-tuned dual-band coupler exhibits 45.9 and 5.2% center operation tuning frequency for the first and the second band, respectively, while 29.2 and 4.3% are achieved by the BST tunable coupler. With two-tone nonlinear characterization test, the BST tunable coupler biased at 0 and 25 V presents a better IP3 of +25.45 and +35 dBm, respectively, while +11.5 and +34 dBm are obtained for the silicon varactor tunable coupler. (c) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:858867, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26719