Abstract: A novel dualmode dualband bandpass filter with simple defected ground structure (DGS) is proposed. A dualmode dualband bandpass filter is obtained by combining a microstrip square loop resonator on the top layer and another square loop constructed with DGS on the bottom layer, which achieve dualmode singleband bandpass characteristic, respectively. Excited with common feed lines, the proposed filter is compact and easy fabrication. The resonance frequencies of these two loops are relatively independent so the design is flexible. Furthermore, an improved resonance unit with quasi CPWDGS is presented to reduce the filter insertion loss by decreasing the radiation loss on the bottom layer. The design is confirmed by simulation and experiment results with good agreement.