A Novel Bandpass Filter Using a Combination of Open-Loop Defected Ground Structure and Half-Wavelength Microstrip Resonators

This paper deals with a defected ground structure (DGS) open-loop resonator analysis and bandpass filter design, using coupled DGS and microstrip resonators. The combination of DGS and microstrip resonators allows using top and bottom sides of the microwave substrate, therefore the resonators can partially overlap and a desired coupling coefficient can be easily achieved. The open-loop DGS resonator properties are investigated, as well as coupling types between the resonators. Finally, two bandpass filters are designed and simulated. The sixth order filter is fabricated and the results are compared with measurement. The introduced structure represents an alternative to a conventional parallel-coupled half wavelength microstrip resonator bandpass filter.