Design of microstrip narrowband bandpass filter using a star shaped defected ground structure

Abstract

This paper introduces a bandpass filter using a new star shaped defected ground structure (DGS). It consists of two coupled star shaped slots with small opening etched on the ground plane and is fed by ‘T’ shaped microstrip feed lines on the top layer of the microstrip. Due to the arrangement of etched slots and also because of capacitive gap between T shaped feed lines which acts as a J inverter, band reject response is converted into a bandpass response. T shaped feed lines provide necessary coupling to achieve bandpass response. A prototype filter simulated shows, an insertion loss of 1.1 dB, return loss of 22 dB and having narrow fractional bandwidth (FBW) of 12.55% centered at 2.42 GHz. With low insertion loss, good return loss, narrow bandwidth, and low cost, the proposed filter is an attractive choice for modern wireless communication systems such as WLAN and Bluetooth applications.