Comparative Study of Three DGS Unit Shapes and Compact Microstrip Low-Pass and Band-Pass Filters Designs

Abstract

In this paper, three types of defected ground structure (DGS) units which are triangularhead (TH), rectang ularhead (RH) and Ushape (US) are investigated. They are further used to lowpass and bandpass filters designs (LPF and BPF) and the obtained performances are examined. The LPF employing RHDGS geometry presents the advantages of compact size, lowinsert ion loss and wide stopband compared to the other filters. It provides cutoff frequency of 2.5 GHz, largest rejection band width of 20 dB from 2.98 to 8.76 GHz, smallest transition region and smallest sharpness of the cutoff frequency. The BPF based on RHDGS has the highest bandwidth (BW) of about 0.74 GHz and the lowest center frequency of 3.24 GHz, whereas the other BPFs have BWs less than 0.7 GHz. Keywords—Defected ground structure (DGS), triangularhead (TH) DGS, rectangularhead (RH) DGS, Ushape (US) D GS, low� In this paper, we present three DGS unit shapes which are triangularhead (TH), rectangularhead (RH) and Us hape (US) and their characteristics are compared. Further, these units are employed in lowpass and bandpass filter s designs and the obtained performances are examined. The simulations are carried out using the fullwave EM IE3D simulat or and all prototypes are designed on substrate material with thickness of 0.25 mm, conductor layer of 35 Em and a relative permittivity of 3.63. The following section of this paper describes the comparison of three DGS units. In Section III, LPFs based on the above DGS units are designed and their characteristics are investigated to determine which one offers the best filter specifications. In Section IV, BPFs based on the DGSs with a discontinuity in the 50 G (characteristic impedance) microstrip line are designed and analyzed. Finally, conclusions are drawn in Section V.