In this article, an adjustable microstrip lowpass filter(LPF) with the cut‐off frequency (f_c) at 1.59 GHz is designed and fabricated. The proposed structure is composed of a Z‐shaped resonator as basic resonator and a combination of modified T‐shaped and Z‐shaped resonators as suppressor units. To describe a theoretical design, the L‐C equivalent circuit of the basic resonator and also its transfer function are calculated precisely; then, the location of the first transmission zero (TZ) is accurately computed. Generating a deep TZ near the cutoff frequency leads to a high roll‐off rate of 195 dB/GH. The LPF also benefits from an extremely wide stopband from 1.72 to 23.67 GHz (15 f_c). In passband region, the insertion loss and return loss of the LPF are 0.62 and 22.9 dB, respectively. The experimental results also show that maximum variation of group delay is only 0.53 ns regarding a negligible figure. The electrical size of the LPF is 0.187 × 0.083 ${\mathrm{\lambda }}_{\mathrm{g}}^2$ (where λ_g is the guided wavelength at 1.59 GHz). Finally, the proposed LPF achieves a high figure of merit of 57 860 deemed a great accomplishment.

中文翻译：

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使用具有低VSWR的Z形谐振器的可调紧凑型微带低通滤波器的新设计

本文设计并制造了一种截止频率（f _c）为1.59 GHz的可调微带低通滤波器（LPF）。所提出的结构由Z形谐振器作为基本谐振器，以及改进的T形和Z形谐振器的组合作为抑制器单元。为了描述理论设计，精确计算了基本谐振器的LC等效电路及其传递函数。然后，精确计算出第一个变速器零位（TZ）的位置。在截止频率附近产生较深的TZ会导致195 dB / GH的高滚降率。LPF还受益于1.72至23.67 GHz（15 f _c）。在通带区域，LPF的插入损耗和回波损耗分别为0.62和22.9 dB。实验结果还表明，对于可忽略的数字，群延迟的最大变化仅为0.53 ns。LPF的电气尺寸为0.187×0.083${\mathrm{\lambda }}_{\mathrm{G}}^2$（其中，λ_克为1.59 GHz的波导波长）。最后，拟议的LPF实现了57860的高品质，这被认为是一项巨大的成就。