Filter arrangement with compensation of poor electrical ground
In a filter arrangement comprising a frequency filter (F) that has a bad or non-ideal ground connection (GC 1, 2, 3, 4, 5, 6, 7 ), the defects arising from bad ground are compensated by a capacitance (CC) coupled in parallel to the frequency filter. The value of the capacitance is chosen between 1 and 50 fF. The filter arrangement may be a receiving filter (RF) in a duplexer (DU).
1. A filter arrangement, comprising
a frequency filter connected between a first terminal and a second terminal, the frequency filter being coupled to a ground connection; and
a capacitive element coupled in parallel to the frequency filter, wherein
a capacitance of the capacitive element is between 1 and 50 fF; and
the capacitive element and an inductive element associated with the ground connection form a resonator, a resonance frequency of the resonator being set within a stop band of the frequency filter.
2. The filter arrangement of claim 1 , wherein the filter arrangement comprises a duplexer (DU).
3. The filter arrangement of one of claim 1 or 2 , wherein the frequency filter is a receiving filter, and wherein the capacitive element is coupled between an input and an output of the receiving filter.
4. The filter arrangement of claim 1 , wherein the frequency filter is a receiving filter of a duplexer, the duplexer comprising the receiving filter and a transmission filter, and wherein the resonance frequency is within a passband of the transmission filter.
5. The filter arrangement of one of claims 1 , 2 , and 4 , wherein the first terminal and the second terminals are input and output terminals of the frequency filter, one of the first terminal and the second terminal being an antenna terminal.