Design of Symmetric Trisection Filters for Compact Low-Temperature Co-Fired Ceramic Realization

In this paper, the design of symmetric bandpass filters with cross-coupled trisections is discussed. The analysis and synthesis is done by well-known matrix manipulation of the lumped element equivalent circuit. The susceptance of the admittance matrix is split up into two separate matrices for capacitive and inductive contributions, which gives more insight into the manipulation of the matrix. Emphasis is put on design of a three-pole bandpass filter with two transmission zeros at the lower side of the passband. Novel solutions for the symmetric topology are derived, having either resonant main coupling or resonant cross-coupling. The potential of the novel topology is demonstrated by a compact realization of a wireless local area network filter at 2450 MHz in low-temperature co-fired ceramic technology. Good agreement between measured and computed results is obtained.