Design of wide stopband bandpass filter using composite right/left handed transimission line

This paper presents a compact structure, which is characterized by mixed electromagnetic coupling of the composite right/left handed transmission line (CRLH-TL) and source-load cross coupling between the input and output ports. This structure can generate three transmission zeros (TZs) near the bandpass without increasing the overall size of the filter. Meanwhile, in order to get a wide stopband, two open stubs are employed to suppress the harmonic response of the CRLH-TL resonators. Using such a compact structure, a wide stopband bandpass filter is designed, fabricated and measured. Good agreements between simulation and experiment results have been achieved, and good performance in bandpass has been observed with a relative 3-dB bandwidth larger than 17%, and the bandwidth of stopband is 4.0f₀ (f ₀=2.1GHz). The dimensions of the proposed filter are 0.061λ_g× 0.073λ_g (i.e.8.4× 10.5mm²).