Design of ultra-wideband filter with tortuously defected ground structure

A novel design method for small ultra-wideband (UWB) filter is proposed by using tortuously defected ground structure (DGS) to solve the problem of larger insertion loss and narrower stop band in the design of UWB filter. Firstly, a tortuous DGS is obtained by using winding shaped slot in the metal ground, and then equivalent circuit models are established according to the structural features of the parallel coupled-line and the transmission line of the tortuous DGS. The correctness of the circuit models is verified by using software HFSS, and the relation between DGS size and equivalent circuit parameters is deduced. The UWB characteristic of the parallel coupled-line and the low-pass/high selective characteristic of the transmission line of tortuous DGS are demonstrated. A simple and high-selective UWB filter is then designed based on the advantages of the two lines. Test results show that the insertion loss of the proposed filter is lower than those of the conventional DGS and the CRLH UWB filters, and that the measured maximum insertion loss is about 0.88 dB and the rejection in the range of 11.75 to 20 GHz is less than -30 dB.