LTCC balanced filter based on a transformer type balun for WLAN 802.11 a application

This paper reports on the design of a balanced filter based on a new transformer type balun. The disadvantages and performance drawbacks of simple second order transformer are discussed and new third order balun structure is proposed. The new structure is realized as broadside coupled lines vertically stacked using multilayer low temperature co-fired ceramic (LTCC) technology. The resulting structure exhibits excellent electrical performance, immunity to manufacturing tolerances and compactness, which allows using this balanced filter as a building block of highly integrated WLAN front-end modules.