A self-diplexing mixed-coupling bandpass filter based on a single slotted substrate-integrated-waveguide (SIW) cavity is proposed. By etching a wide slot, two unequal half-mode SIW parts are constructed and then fed by four coaxial ports to realise two bandpass filters with different centre frequencies. Since this etched slot can serve as a divider and an isolator, a flexible frequency ratio of 0.60–1.66 and high isolation of better than 20.0 dB is achieved. By further cutting the other two narrow slots, four quarter-mode sub-cavities are obtained where the mixed coupling is induced in the pass bands and a transmission zero (TZ) is introduced at the stopbands. The coupling and TZ are controllable by simply adjusting the length of these cut slots, which makes the proposed design easily redesigned for practical applications. A prototype with a size of 0.59λ 0 × 0.59λ 0 × 0.03λ 0 has been fabricated. The measured centre frequency, TZ, 3-dB bandwidth, and insertion loss of the lower pass band is 2.51 GHz, 2.96 GHz, 340 MHz, and 1.67 dB, respectively, whereas those of the upper pass band is 3.06 GHz, 2.53 GHz, 370 MHz, and 2.44 dB, respectively.

中文翻译：

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基于单槽SIW腔的自双工混合耦合带通滤波器

提出了一种基于单个开槽衬底集成波导 (SIW) 腔的自双工混合耦合带通滤波器。通过蚀刻一个宽槽，构造两个不等长的半模SIW部分，然后由四个同轴端口馈入，实现两个不同中心频率的带通滤波器。由于该蚀刻槽可用作分频器和隔离器，因此实现了 0.60–1.66 的灵活频率比和优于 20.0 dB 的高隔离度。通过进一步切割其他两个窄槽，获得四个四分之一模子腔，其中在通带中感应混合耦合，并在阻带处引入传输零 (TZ)。通过简单地调整这些切割槽的长度，耦合和 TZ 是可控的，这使得所提出的设计很容易为实际应用重新设计。已经制作了尺寸为 0.59λ 0 × 0.59λ 0 × 0.03λ 0 的原型。测得的下通带的中心频率、TZ、3-dB 带宽和插入损耗分别为 2.51 GHz、2.96 GHz、340 MHz 和 1.67 dB，而上通带的测量值分别为 3.06 GHz、2.53 GHz，分别为 370 MHz 和 2.44 dB。