Compact, tunable and wide band stop filter (BSF) for wireless application is presented. The proposed filter is composed of compact rectangular microstrip open loop resonator with stub loaded resonator as building blocks of the filter. First, two vertical lumped capacitors are inserted in the open loop resonator from top to bottom of the substrate at the place which has maximum electric field to decrease the resonance frequency which in turn miniaturize the filter size. The resonance frequency of the fundamental mode is shifted from 5.5 to 4.2 GHz when lumped capacitors of 0.2 pF are added. Second, the capacitance of the open-ended stub can be changed to control the second resonance mode of the filter. Also, by inserting another vertical capacitor at the end of the open-ended stub, the second resonance mode can be controlled and reduced. Finally, by properly selecting the capacitance of the third lumped capacitor, the second resonance mode can be designed to be close to the fundamental mode and hence wide band stop filter can be achieved. The proposed BSF has some appropriate features such as compact size (its size has more than 40% size reduction), wide stopband and most importantly tunability of stopband. The band stop filter has a center frequency of 6.2 GHz, a stop band from 3.5 to 9 GHz, insertion loss lower than − 30 dB, and a return loss higher than 0.4 dB is accomplished inside the stop band. The measured results have good matching with the simulated results.

提出了用于无线应用的紧凑，可调和宽带阻带滤波器（BSF）。所提出的滤波器由紧凑的矩形微带开环谐振器组成，其中短截线加载谐振器作为滤波器的构建块。首先，将两个垂直集总电容器从基板的顶部到底部在具有最大电场的位置插入开环谐振器中，以减小谐振频率，从而使滤波器尺寸最小化。当添加0.2 pF的集总电容器时，基本模式的谐振频率从5.5 GHz移至4.2 GHz。第二，可以改变开放式短截线的电容，以控制滤波器的第二谐振模式。而且，通过在端部开口端的末端插入另一个垂直电容器，可以控制和减小第二谐振模式。最后，通过适当地选择第三集总电容器的电容，可以将第二谐振模式设计为​​接近基本模式，从而可以实现宽带截止滤波器。提议的BSF具有一些适当的功能，例如紧凑的尺寸（尺寸减小了40％以上），宽的阻带以及最重要的是阻带的可调性。带阻滤波器的中心频率为6.2 GHz，阻带范围为3.5至9 GHz，插入损耗低于− 30 dB，回波损耗高于0.4 dB。测量结果与模拟结果吻合良好。提议的BSF具有一些适当的功能，例如紧凑的尺寸（尺寸减小了40％以上），宽的阻带以及最重要的是阻带的可调性。带阻滤波器的中心频率为6.2 GHz，阻带范围为3.5至9 GHz，插入损耗低于− 30 dB，回波损耗高于0.4 dB。测量结果与模拟结果吻合良好。提议的BSF具有一些适当的功能，例如紧凑的尺寸（尺寸减小了40％以上），宽的阻带以及最重要的是阻带的可调性。带阻滤波器的中心频率为6.2 GHz，阻带范围为3.5至9 GHz，插入损耗低于− 30 dB，回波损耗高于0.4 dB。测量结果与模拟结果吻合良好。