Microwave filter design using the defected ground plane

Abstract

The Defected Ground Structure (DGS) is an evolution of one or a few of the photonic band gap (PBG) etched ground elements and is realized by etching off arbitrary defected patterns in the backside metallic ground plane. Unlike the periodic PBG structure, the DGS can be periodic or non-periodic and has relatively simpler equivalent lumped L-C circuit structure. DGS has been extensively used for microstrip component designs in radio frequency and microwave circuits owing to many advantages, such like circuitry size reduction, power handling capability and excellent bandgap effects in certain frequency ranges. A number of microwave circuits have been proposed by using the DGS to reject harmonics and minimize noise figures so as to improve their performance. Historically, the microstrip line with dumbbell-shaped DGS unit and its equivalent circuit was proposed and verified. An improved DGS and compensated microstrip line have also been proposed for filter design to enhance the bandgap properties. In this report, A novel microwave low pass filter with wide rejection band, designed by etching five fork-shaped DGS patterns in metallic ground plane, is proposed. The 20-dB rejection bandwidth, return loss, insertion loss, 3-dB cutoff frequency as well as the selectively of the filter are measured.