A multiband bandpass filter using interdigital and step-impedance techniques for 4G, WiMAX and WLAN systems

This paper proposes a multiband bandpass filter using interdigital and step-impedance techniques for 4G, WiMAX and WLAN systems. The step-impedance resonator can control fundamental and harmonic frequencies, while the size of resonator can be reduced by using interdigital technique. The multiband includes 2 sets of bands: the first set has responses at 1.8 GHz, and 3.7GHz, and the second set has responses at 2.45 GHz, and 5.5 GHz. The cross coupling technique has been employed to combine all of these frequency bands. The experimental results of the fabricated filter agree very well with simulation expectations using IE3D package. The proposed filter has good performances with resonator size reduction (from λ/2 to λ/8).