SMALL-SIZED MICROS TRIP LOWPASS FILTER USING DEFECTED GROUND STRUCTURE

Microstrip lowpass filter plays important role in many RF or microwave applications.
They are used to select the microwave signals within assigned spectral limits. 1n this
project, a conventional stepped-impedance microstrip lowpass filter is designed to
have an equal-ripple response with a cutoff frequency of 0. 8 GHz. The filter needs to
satisfy more than 20 dB insertion loss at 1.2 GHz with the impedance of 50 Ohm. By
using the insertion loss method, filter performance is expected to be improved at the
expense of a higher order filter. Another filter with the defected ground structure
(DGS), having the same physical length, is introduced to investigate the performance
of the filter. The simulation is carried out using the Agilent Advanced Design System
(ADS) and Sonnet Suite software and in the experimental measurements a vector
network analyzer is used. The results taken from the measurement shows that the
signal response from the filter with DGS exhibits a wider passband frequency, with
sharp cut off frequency. Another filter with defected microstrip structure (DMS) also
shows the same behavior. The discontinuities structure proves that it can be used to
improve the performance and reduces the size of the filter.