Patent ID: 7619495

Claim:
A bandpass filter comprising: a planar transmission medium comprising a transmission line, said transmission line comprising a conductor strip, said bandpass filter having, in said transmission line, at least one bandpass filter cell, said filter cell comprising at least one split-rings resonator, at least one inductive element and at least one capacitive element, said bandpass filter having a frequency response in which at least one passband can be identified, wherein said conductor strip, said at least one split-rings resonator, said at least one inductive element and said at least one capacitive element being dimensioned and arranged so that the bandpass filter, for frequencies within said passband, behaves as a left-handed transmission line for at least one range of frequencies within said passband, and as a right-handed transmission line for at least another range of frequencies within said passband, and wherein said at least one cell features a T equivalent circuit having a series impedance and a shunt impedance, wherein, for one frequency band within a passband of the bandpass filter, the series impedance of the cell is negative and the shunt impedance is positive, wherein, for another frequency band within the same passband, the series impedance of the cell is positive and the shunt impedance is negative, and wherein, at a frequency between said frequency bands, the series impedance is substantially null and the shunt impedance is substantially infinite.