The design of a compact quasi-elliptic filter using stepped impedance resonators with harmonic suppression

A bandpass filter is designed at 2.4 GHz using two end-1 connected quarter-wavelength stepped impedance resonators. The quarter-wavelength stepped impedance resonators having one end shorted are formed by a half-wavelength stepped impedance resonator with its middle shorting to ground. The modes that the shorted-end lambda/4 stepped impedance resonator supports are the (1 + 2n)/4. An enhanced U-shape coupling feed is adopted in the filter design to reduce the insertion losses as well as to suppress the first higher harmonic. A dual-path design is implemented in the proposed filter to create a quasi-elliptic frequency response. The equivalent circuit model is developed and the experiments are conducted for circuit design verification. (c) 2007 Wiley Periodicals, Inc.