Comparative Study of a Micro-strip Line with DGS and without DGS

The low pass filter is used in many application of microwave communication. Therefore it is necessary to design a good low pass filter for the faithful reproduction of wanted signals. Previously used methods to design the low pass filter using insertion loss method don’t give a very good flat response. So, a new method has been proposed for the filter design which gives a good response as compared to the conventional designs. A new DGS (Defected Ground Structure) technique to design a low pass filter is proposed here, ground is defected or cut in a desired shape which improves its performance. The size of filter is also reduced with the help of DGS. INDEX TERMS –LPF, DGS, MICROSTRIP INTRODUCTION Microwave system often requires means for suppressing unwanted signals and/or separating signals having different frequencies. These functions are performed by electric filters. Filters are usually categorised by their frequency characteristics, namely low-pass, high-pass, bandpass and bandstop. The first objective is to study about the conventional microwave Low Pass Filter (LPF). The second objective is to study about Low Pass Filter using Defected Ground Structure (DGS). When a conventional low pass filter (using capacitor, inductor etc.) is used for suppressing unwanted signals or separating signals having different frequencies, it shows discontinuity elements and has repeated high impedance. A defective ground structure (DGS) is an internally designed defect on a ground plane that creates additional effective inductance and capacitance .The technique can be used to design microstrip line with desired characteristics, thus significantly reducing the foot print of the microstrip structure. Microstrip Filter A microwave filter is a two-port network used to control the frequency response at a certain point in a microwave system by providing transmission at frequencies within the passband of the filter and attenuation in stopband of the filter. The general structure of a microstrip is illustrated in figure 1. A conducting strip (microstrip line) with a width W and a thickness t is on the top of a dielectric substrate that has a relative dielectric constant r  and a thickness h, and the bottom of the substrate is a ground (conducting) plane. Figure: 1 General microstrip structure. Guided Wavelength, Propagation Constant, Phase Velocity, and Electrical Length The guided wavelength of microstrip is given by