Research And Design Of Ultra-wideband Balun Based On LTCC Technology

In order to meet the needs of all things interconnected in the future,wireless communication system is developing rapidly.The arrival of the fifth generation of communication technology(5G)era means high standards and high requirements for RF front-end circuit design,among which ultra-wideband,low-cost microwave passive devices are the hot spot of research at home and abroad.As a converter for balanced and unbalanced ports,ultra-wideband balun is often used as the main part of the balanced feed in the antenna system to achieve impedance matching.Low temperature co-fired ceramic(LTCC)technology facilitates miniaturization and high performance of microwave passive devices through lamination and three-dimensional integration.The content of this paper is about the ultra-wideband balun based on LTCC technology.Analysis and optimization of many different structures has been made,and the effective methods to improve its bandwidth are proposed.Finally the following research results are achieved:(1)Two ultra-wideband baluns based on the Marchand balun are designed,using a wide-edge spiral-coupling stripline of strong coupling to increase the bandwidth.Two structures are proposed to improve the ultra-wideband characteristics: One is to increase the number of coupled lines,another is to load the capacitor at the end of the coupled line.The two ultra-wideband baluns are both processed and tested,achieving 100% and 83% relative bandwidth and smaller than 3.2mm x 4.5mm x 1.5mm.(2)An uncoupled ultra-wideband power split balun is designed,which consists of a combination of a second-order ultra-wideband power divider and an uncoupled 180° ultra-wideband phase shifter.The former is realized by curved strip lines,eliminating the discontinuity of the electrical performance at corners.The latter is achieved by the transmission line loading the open-and short-circuit branches.The vertical cascading of two single components is completed,and the ultra-wideband balun is miniaturized by the laminated structure,and the processing test is performed,finally achieving 73% relative bandwidth and high isolation.The size is smaller than 3.2 mm× 4.5mm x 1.5mm.(3)A coupled ultra-wideband power split balun is designed,which consists of a combination of a third-order ultra-wideband power divider and a coupled ± 90° ultra-wideband phase shifter.The former adds the order of impedance transformation on the basis of the second order to increased the bandwidth,and the latter is realized by a high coupling degree Lange coupler with a stereo coupling and a planar interconnection.The vertical cascading of two single components is completed,and shield isolation was used to reduce crosstalk.After debugging,an ultra-wideband balun with a relative bandwidth of 102% is realized,and the size is small than 3.2 mm×4.5 mm×1.98 mm.