Microstrip Bandpass Filters Using Window Hairpin Resonator and T-Feeder Coupling Lines

A new structure of planar window hairpin-based bandpass filters with symmetrical T-shaped feeder coupling line resonators is introduced. With varying different width in X axis and length in Y axis of the window of the hairpin resonator configuration, correspondingly the changes can be observed in the resonant frequency and useable bandwidth. By these methods, frequency tuning can be easily achieved by adjusting hairpin window dimension of the structure. Both filters were designed for 5.205 GHz resonant frequency. The geometrical window hairpin structure areas of both type filters are quite similar and both filters are resonated at almost the same frequency. The measurement results show that return loss (S-11) for both filters is higher than 23.0 dB and insertion loss (S-21) is measured less than -1.4 dB at resonant frequency of 5.13 GHz. The S-parameter responses of the fabricated filter nearly match with the electromagnetic simulated results; therefore, the feasibility of practical application of the proposed filters can be expected.