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| Design for Miniature Filter with Ultra-wide Stopband Based on Open-Stub T-shaped Structure |
| Zhu Yi-zhi①② Zhang Xiao-juan① Fang Guang-you① |
①(Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China)
②(Graduate University of Chinese Academy of Sciences, Beijing 100049, China) |
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Abstract Conventional filters always suffer from the interference of its spurious bands, which leads to poor stopband in high frequency range. With the development of ultra-wide band radar system and ultra-wide band communication system, filters with minitype and wide-stopband become an urgent technique challenge. In this paper, a general design of miniature filter with ultra-wide stopband based on open-stub T-shaped structure is demonstrated. Comparing with conventional filters, this type of filters have compact structure, good passband characteristics and its spurious bands whtiin the fifth order harmonic frequency range are all suppressed. A lowpass filter with cutoff frequency at 2.9GHz is designed with the proposed structure. The measured average insertion loss is only 0.67dB, average VSWR is only 1.33. Its transition band is steep and its 40dB square ratio is 1.096. The measured 36dB stopband ranges from 3.23GHz to 10.30GHz and 27dB stopband ranges from 10.30GHz to 15GHz. Moreover, its length is only 37.1% of the conventional substitutional filter, with much less area and more compact layout. The simulated and measured results indicate that this open-stub T-shaped filter satisfies the demand of both minitype and wide-stopband.
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Received: 17 July 2009
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Corresponding Authors:
Zhang Xiao-juan
E-mail: xjzhang@mail.ie.ac.cn
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2010, Vol. 32 
