Hybrid Transfer Function Transformation Methodology Based on Spiral Notch Filters

A hybrid transformation methodology for the frequency response of filters with tunable characteristics is presented in this paper. This method is well-suited for discrete implementation of filters, which helps to achieve a desired transfer function and overcome discrete implementation functionality limitations. The proposed hybrid method benefits composition of Spiral Defected Microstrip Filters (DMF) as band-reject filters. New formulations are extracted to introduce a systematic design process by using a numerical analysis and Levenberg-Marquardt iteration algorithm. Test boards have been realized on RT/Duriod4003c substrate of ε
_r
=3.85 for validation. Moreover, we have designed and fabricated two hybrid filters as case studies. In the first case, the methodology is used to eliminate the unwanted frequency band of 1.5 GHz. The second case involves bandwidth reduction from 900 MHz to 700 MHz. Each spiral DMF occupies 100 mm
²
area. The return loss and group delay of the individual filter are less than 0.48 dB and 0.5 ns, respectively.