A design methodology for a small-size multifunctional quad-band bandpass filter (BPF) exhibiting high selectivity is proposed in this study. In this design, the resulting BPF would comprise a dual-band split-type BPF, wideband BPF and narrowband BPF, and it can execute narrowband/wideband operation and provide close/wideband spacing. Since each passband can be formed by respective filters, the design methodology has high flexibility in that it can achieve different filter functions and can be compatible with various communication systems. In addition, because of the source-load coupling, four additional transmission zeros could be created over the stopband, thus enhancing the selectivity. A quad-band BPF operating at 1.45/1.65/4/6GHz with fractional bandwidths of 6.6/5.8/35/3% was implemented to verify the design methodology. The fabricated BPF was determined to have a compact circuit size of 0.3 λ _g × 0.44 λ _g ( λ _g is the guided wavelength at the central frequency of the first passband) and it exhibited an in-band insertion loss of no more than 2.8dB. The experimental and simulation results were determined to be in good agreement.

中文翻译：

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具有可控制带宽和频带间隔的微带四频带通滤波器的设计，用于多功能应用

本研究提出了一种具有高选择性的小型多功能四频带通滤波器（BPF）的设计方法。在这种设计中，所得的BPF将包括双频带分离型BPF，宽带BPF和窄带BPF，并且它可以执行窄带/宽带操作并提供近/宽带间隔。由于每个通带可以由各自的滤波器形成，因此设计方法具有高度的灵活性，因为它可以实现不同的滤波器功能，并且可以与各种通信系统兼容。另外，由于源－负载耦合，可以在阻带上创建四个附加的传输零，从而提高了选择性。实施了工作于1.45 / 1.65 / 4 / 6GHz且带宽为6.6 / 5.8 / 35/3％的四频BPF，以验证设计方法。λ _克×0.44 λ _克（ λ _克是在第一通频带的中心频率的导波波长），并显示出它不超过2.8分贝带内插入损耗。实验和仿真结果确定为吻合良好。