A narrow‐band bandpass filter (BPF) based on parallel coupled lines and shorted stubs with very wide upper stopband has been presented. The transmission coefficient and reflection coefficient of the proposed BPF are straightforwardly derived via the input impedances using odd‐ and even‐mode analysis method. The calculation results illustrate that two narrow passbands with very high frequency ratio of the upper‐band to lower‐band center frequencies can be realized, which is significantly suitable to design a narrow‐band BPF with very wide upper stopband. To verify the proposed design idea, a narrow‐band BPF example was designed and experimentally characterized, whose measured in‐band return loss is >30 dB with center frequency at 1.76 GHz. The measured upper stopband is up to 14.34 GHz with the rejection levels of over 20 dB.

中文翻译：

---

窄带通滤波器，具有非常宽的上阻带

提出了一种基于并行耦合线和具有很宽的上阻带的短截线的窄带带通滤波器（BPF）。所提出的BPF的传输系数和反射系数可以通过输入阻抗使用奇模和偶模分析方法直接得出。计算结果表明，可以实现两个高通频带与低通频带中心频率之比很高的窄通带，这非常适合于设计高通频带的窄带BPF。为了验证所提出的设计思想，设计并通过实验表征了一个窄带BPF实例，在中心频率为1.76 GHz时，测得的带内回波损耗> 30 dB。测得的上限带高达14.34 GHz，抑制水平超过20 dB。