Abstract
A lowpass filter with wide stopband based on stepped impedance hairpin resonator is proposed. Multiple transmission zeros are created in the stopband region by different size T-shaped resonator to achieve wide stopband. A lowpass filter with 3dB cutoff frequency (fc) at 3.2GHz is designed, simulated and fabricated. Experimental results indicate that stopband can be extended to more than 7fc with a rejection level of 20dB after loading T-shaped resonator. The insertion loss is lower than 0.4dB and return loss is better than 16dB in the passband. Excluding the feed lines, the size of the filter is less than 0.26λg X 0.06λg. The modified filter is of good value in engineering application for its small size, sharp cutoff frequency response and wide stopband.
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