基于开路T型结构的小型化超宽阻带滤波器设计

传统滤波器由于寄生通带的存在,其高频阻带性能较差.随着超宽带雷达系统和超宽带通信系统的发展,小型化宽阻带的滤波器已成为一项紧迫的技术课题.该文论述了一种普适性的基于开路T型结构的小型化超宽阻带滤波器结构,这种滤波器和传统滤波器相比,结构极为紧凑,5倍基频范围内的寄生通带均被抑制,而通带性能保持良好.基于此结构实际制作了一个截止频率为2.9 GHz的低通滤波器,测量得到的通带内平均插入损耗仅0.67 dB,带内平均驻波比为1.33,过渡带陡峭,40 dB矩形系数仅1.096,而所测得的阻带从3.23 GHz到10.30 GHz之内谐波抑制大于36 dB,从10.30 GHz到15 GHz之内谐波抑制大于27 dB;该滤波器的长度仅为传统的同类型滤波器的长度的37.1%,面积大大减小.仿真和测量结果表明该类型滤波器同时满足了小型化和宽阻带的性能需求.

Design for Miniature Filter with Ultra-wide Stopband Based on Open-Stub T-shaped Structure

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.