Patent ID: 8981872
Filing Date: 2015-03-17
Classification: H03H

Abstract:
1. An antenna duplexer, comprising: a transmission filter that operates in a transmission frequency band and has a transmission filter output, a reception filter that operates in a reception frequency band and has a reception filter input, an antenna connection connected to an output of the transmission filter, and a matching element connected between the antenna connection and an input of the reception filter, wherein the reception filter comprises a ladder-type filter circuit disposed on an antenna side of the reception filter, the reception filter further comprising a double mode surface acoustic wave (DMS) filter, wherein the ladder-type filter circuit comprises interdigital structures that are each connected in parallel with a series resonator, the interdigital structures comprising electrode fingers aligned on a piezoelectric substrate to produce a negligible electro acoustic coupling coefficient, wherein a first element on the input of the reception filter is a parallel resonator, wherein the matching element transforms an impedance of the reception filter in the range between 50 and 75 percent of a mid-frequency of the reception frequency band to a short circuit, and wherein the matching element together with the transmission filter and the reception filter, attenuates transmission signals by at least 40 dB in a frequency band whose frequencies f are in the interval 0.50*f